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Driving for Maximum Fuel Efficiency

By Liar in Technology
Wed Jun 06, 2007 at 12:00:00 PM EST
Tags: cars, trucks, driving, fuel efficiency (all tags)

I'm strange. I love to measure things. I've used a GPS receiver to find the optimal parking situation at work, I measure the costs of meetings (based on estimates of what I think people make), and I've even measured the effects of different driving techniques and the resulting impact on fuel economy. Yes, I'm strange.


Depending on how you define "easy", the easiest way to improve fuel efficiency is to buy a newer more fuel efficient car. This, however, is not always practical and college students in general just drive whatever they can get for $300 and a used Aerosmith CD. But, if you are in a market for a new car and the hybrids don't serve your needs, keep in mind that manual transmission (stick shift) will eventually be the most economic choice especially when coupled with some driving strategies I'll shortly write about.

Another technique is to abandon your car as much as possible. Bike, take the bus, walk. The exercise will be good for you, too. Yet again, circumstances can make this option difficult.

Therefore, if you do commute to work, drive to your friends, truck over to the grocery store, or motor to the movies, the following are some driving tips that will make the trip more fuel efficient. These techniques can be observed from the forums of enthusiastic hobbyists who take fuel economy seriously. They're called hypermilers and in competition often achieve unbelievable rates of fuel consumption. Unsurprisingly, the typical hypermiler wrings the most from a hybrid car so some advice on their forums cannot be used on non-hybrid cars, including the common technique known as the pulse and glide (P&G--acronyms are very popular in hypermiler forums).

The basics of fuel efficiency can typically be found in your owners manual: scheduled tune ups, properly inflated tires, oil and filter changes at the recommended schedule. Some hypermilers recommend using thinner oil but at this time I haven't developed any numbers on this to verify, though it seems like solid advice and I'm currently trying it out. Other hypermilers recommend over-inflating tires by a few PSI and they've reported no additional wear on their tires. Take this information advisedly though as anything above manufacturer's recommendations can become a potential hazard. I'd like to thank The Spins for insisting that some of this information be mentioned and point you to his comment for additional tactics.

The hypermilers with the best fuel efficiency can generally engage in unsafe habits. In a Washington Post article from almost a year ago, an expert reviewed the common techniques and some were found to be benign while others were deemed outright dangerous, so if you're determined to be a hypermiler, please don't take this article as an encouragement to adopt all of their techniques carelessly.

I've found that it's possible to adopt some of their techniques and even modify some of the less-lethal-but-still-unwise techniques to use less fuel on my daily commute. By using these techniques, it was fairly easy to boost my fuel efficiency from 27.1 mpg (miles per gallon, 11.52 km per liter for you metric heathens) to 32.5 mpg (13.82 km/L). This is almost a net gain of 20%. It takes at most a couple minutes longer to arrive at my destination and it takes not much extra effort. This article demands this phrase though: your mileage may vary.

The main thing to keep in mind is that the purpose of using fuel is to accelerate, not to achieve a particular speed. This is an abstract but important way to look at the situation. So, for example, if you keep burning fuel at the same rate going up a hill as well as driving where it's flat, you will lose speed going up the hill by comparison. Now, if you can think in this particular way, a lot of other pieces fall in to place and much of this advice is going to come naturally to you. So, let's look at actual driving techniques.

Drive at non-standard times This is not always possible but in order to do many of the other techniques that I'll describe, it helps to have as much road available to you as possible. If you're stuck in rush hour traffic, no technique can help you--you're driving at the mercy of the Traffic Gods and they demand petroleum sacrifices.

Brake sparingly In fact, learn to hate your brakes. Braking is a sign that you've used too much fuel and now you're going to let some of that acceleration that you've built up go to waste. The ideal is to use nature to your advantage as much as possible, timing your fuel consumption and then letting your car decelerate on its own so that when you stop, you end up perfectly where you intended. That's the ideal. In practice, this means to take advantage of every hill whose top contains a stop sign, going perhaps a little faster than typical around turns, and not tailgating the car in front of you so that you won't be switching between gas and brake in response to the driver in front of you.

Draft Learn from the professionals. While I discourage tail-gating as being both dangerous as well as non-fuel efficient, our normal road ways offer plenty of opportunities for drafting safely: big vehicles. Enormous diesels cut a wide swath through the air reducing wind resistance which you can sail through to see a modest improvement in efficiency. My car has a built in gauge that lets me monitor my fuel burn rate and the savings here can be enormous; it's not atypical to improve my fuel efficiency by more than 50% just by drafting alone. Of course, do this safely by giving enough room between you and the vehicle in front of you that it doesn't increase the possibility of an accident. I find that I get decent drafting even three or four car lengths behind a big rig and a measureable boost even behind a Dodge Durango when trailing by that same distance. Of course, three or four car lengths is more than most people give anyway.

Slow Down You move too fast. You got to make the morning last. Kicking down the cobblestones... With all due respect to the prescient Simon and the permed Garfunkel, they are giving some good advice. The speed limit is generally as fast as you should go. The U.S. government website FuelEconomy.gov advises that all speeds over 60 mph decreases fuel efficiency. Many hypermilers observe it more conservatively, achieving top efficiency at speeds as low as 40 mph. Since each car is different, it's difficult to say what speed is most efficient for your car, but I find my car operates best between 50 and 55 mph. So, generally, avoid speeding unless (and I hesitate to recommend breaking a law) you're going down hill in which case take full advantage of the fuel-free acceleration nature is giving you.

A word to those who talk about driving with the flow of traffic. As always, safety should be your primary concern when driving but the road belongs to you as much as anyone else. You'll generally only be an obstacle to those behind you so be courteous and allow others to pass you, stay out of the fast lane, and if you're on a one lane road with cars stacking up behind you give some consideration to breaking the rules of hypermiling to avoid an unnecessary bullet. Don't let your speed drop to less than what you feel comfortable getting away with safely. That said, in the past 6 months in which I've been adopting these techniques, it has never created a problem--most people know just to move over a lane to pass you. You'll also find more people driving at these speeds than you've realized.

Of course, if you're drafting off a grocery store truck, his speed is your own.

Let others Jack Rabbit start The light turns green and you lead foot the gas to get up to speed as fast as possible, right? Wrong! You're burning fuel at a much greater rate than you need to. If your foot is all the way to the floor, you're just dumping fuel into the engine while you're only going 10, 15, and 20 miles per hour. That's not efficient. Do it at a measured and even pace. There is a sweet spot for accelerating at the peak of your car's torque curve, and some experimenting and measuring will help you find it. But the jack rabbit starts are just not efficient.

Pay attention It's easy to get so caught up in driving that you lose track of these techniques. Measuring your speed can become a full time pre-occupation while you're on the road. You need to look far enough ahead to anticipate the road conditions (and not brake accordingly). Be aware of your trip so that you know that the big hill that leads up to your place requires a slightly different driving style than when you are going down that hill on your way to work. Perhaps even route yourself around that hill and along a more gentle slope. It greatly helps if your car has a gauge that tracks fuel consumption. Use that in order to determine the speeds at which your own car best operates.

There are several popular discussion boards where the members trade fuel economy tricks. The two most popular that I've found are GreenHybrid.com and CleanMPG.com. CleanMpg has an excellent discussion page examining the whys and hows of EPA standards and hypermiling that is worth considering.

It's sometimes embarrassing how much fuel we waste. Sure, it's fun to tear up that on-ramp, but at the end of the day, if you use these techniques, you get to feel superior to everyone else driving like maniacs around you. You can't put a price tag on that. Also, the planet will thank you. Think of the children.

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Driving for Maximum Fuel Efficiency | 176 comments (152 topical, 24 editorial, 10 hidden)
manual transmissions (none / 1) (#1)
by GhostOfTiber on Wed Jun 06, 2007 at 11:39:15 AM EST

Explain it more for the people who don't know how to drive a proper transmission.

Talk about the CVT transmission also.  There's a Nissan commercial where the guy is making engine noises, but in reality the thing makes a weird wirrrrr noise as it moves the pinion on the planes.

[Nimey's] wife's ass is my cocksheath. - undermyne

unfortunately, it gets too specific (none / 1) (#15)
by Liar on Wed Jun 06, 2007 at 03:37:23 PM EST

each gear has a specific point (fuel doesn't burn as a simple function of speed or RPMs) at which it operates optimally and if you're switching between gears, the strategies change depending on if you're accelerating or decelerating. Switching between 1st and 2nd is different from switching from 1st to 3rd which is different from switching from 4th to 5th.

Also, it becomes advice specific to owners of a particular type of car and I wanted to offer advice that anyone can use regardless of what type of car they were driving.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
I would still mention it (3.00 / 2) (#21)
by GhostOfTiber on Wed Jun 06, 2007 at 04:24:52 PM EST

It's not terribly complicated.  The most optimum burn of fuel is the lightest you can hit the gas to maintain speed at a particular RPM.

In other words, 5th gear is less efficient than 4th gear at 40 MPH despite the revs being lower if you have to floor the car to keep it moving.  On the other hand, at 70mph you'll be burning gas like it's water in 4th because the engine is spinning so fast the EFI system is pounding gasoline in there out of fear of leaning out the engine spinning it so quickly.  Obviously your milage may vary, but the Rule of Thumb is that if your RPM drop is more than twice what it would be if you had shifted sooner to the next gear, you could be doing better.  So if 1st to 2nd is losing 1000 rpm from 3000 rpm, you're pretty much wasting gas past 3000 or 4000 rpm.  My MR2, for instance, loses almost 3000 rpm between gears at the redline, but only 1000 rpm between gears at half that.  To make it even simpler, shift halfway through the tach for an NA car.  This is much easier to graph than to type, but the idea is to maximize the mechanical advantage of the engine by keeping the gears really low.  Spinning it quickly doesn't change the mass, so your best bet is to screw around with the gears.  Or running the engine up to the redline and dumping the clutch so the mass is doing all the work which is fun in a rental.

Anyone with the newer EFI which controls the throttlebody has an even easier time:  Lower RPMs do equal more efficiency simply because you're not in direct control of the air and gas anymore.  The simple way to tell is to open the airbox so you can see the plate and press the accelerator to the floor.  If the throttlebody opens fully, it's the old EFI system (or not EFI at all). If it doesn't open fully (or doesn't move), it's the new EFI system.  

Or you broke it.

[Nimey's] wife's ass is my cocksheath. - undermyne
[ Parent ]

mind adding this as a topical comment? (none / 1) (#24)
by Liar on Wed Jun 06, 2007 at 04:57:33 PM EST

part of the point of an article like this is to get other people to share their knowledge and ideas on how to do it. Otherwise, there's little to discuss.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
CVT Noise (none / 1) (#152)
by Trevasel on Wed Jun 13, 2007 at 12:10:53 PM EST

Many of the CV transmissions in the US are programmer to go through a wide RPM range and shift abruptly because American consumers got confused and complained about the transmission sound, thinking it wasn't working. I think this is getting rarer, fortunately.
-- That which does not kill you only makes you stranger - Trevor Goodchild
[ Parent ]
The most efficient way of driving, I'm told, (3.00 / 2) (#3)
by Elija on Wed Jun 06, 2007 at 12:11:42 PM EST

is to accelerate quickly up to some high speed (probably about 100 km/h), then put the clutch down, switch off the engine and coast till the car has almost stopped, then start the engine again, using the car's momentum rather than the starter motor, and repeat.

Unfortunately, this is illegal in most places.

Even if you don't switch the engine off and coast with the engine turning over this is still much more efficient (I'm told) than driving at a constant speed.

Incidently, which constant speed gives you the best fuel efficiency for a typical car?

Another question for car-engine-geeks: is it normal nowadays for a car to achieve its top speed in its highest gear, or in its second-highest gear? (I've come across both cases.)


old cars (2.50 / 2) (#6)
by diskis on Wed Jun 06, 2007 at 12:34:49 PM EST

That doesn't apply for modern (less than 10 years old) cars. Direct injection keeps the fuel flow optimal. Cars without direct injection can burn more gas than needed to sustain the current velocity.

Same with the gears. Old cars, and the highest gear was for economic driving at highway speeds. Lower RPM = lower fuel consumption.

Direct injection again, and you can redline the car and it still uses the same amount of gas as when driving calmly. In these cases the gearbox is designed with usability, and not economy in mind.

[ Parent ]

Uh, try again (3.00 / 4) (#25)
by jasyoung on Wed Jun 06, 2007 at 05:02:59 PM EST

As a minor point, true gasoline direct injection does exist but isn't yet tremendously common. By direct injection I'm talking about technologies such as Volkswagen's FSI. Multiport fuel injection is still the standard system these days, which is not direct. There's an injector per cylinder, but those injectors are in the intake manifold behind the intake valves.

This bit about "you can redline the car and it still uses the same amount of gas as when driving calmly" is nuts. Fuel consumption is a function of airflow through the engine. Modern cars use sophisticated management to keep the air:fuel ratio highly controlled. Airflow obviously goes up with RPM, and is also a function of the throttle opening. This is not some sort of earth-shattering change in physics from the days of the carbuerator, just a far more precise and flexible way to dial in the right amount of fuel for a given set of conditions.

[ Parent ]

Not all 'metric heathens' use km per litre (1.50 / 2) (#4)
by Elija on Wed Jun 06, 2007 at 12:17:08 PM EST

Germans use litres per 100 km.


So do Australians ... (none / 1) (#159)
by brad0 on Sat Jun 16, 2007 at 06:18:32 AM EST

Even though km/l would make mental calculations of "how far will I get on the 5 litres remaining in the tank" easier.

[ Parent ]
And French... (none / 1) (#165)
by MartiCode on Mon Jun 18, 2007 at 12:40:15 PM EST

In fact I think it is pretty standard in all of Europe. My car computer has only two settings : mpg or l/100.

--
{ Cooking blog | French Restaurants Guide }
[ Parent ]
Eh? (none / 1) (#171)
by Canar on Tue Jun 26, 2007 at 11:21:12 PM EST

And Canada too!

[ Parent ]
And portuguese. <nt> (none / 1) (#172)
by Vesperto on Sun Jul 01, 2007 at 08:58:00 PM EST


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[ Parent ]
What, no numbers? (3.00 / 3) (#5)
by gndn on Wed Jun 06, 2007 at 12:25:56 PM EST

What kind of analysis is this? You don't even attempt to provide any dollar figures for amounts saved while following these driving tips versus driving like a jackass. Yeah, you went from 27mpg to 32mpg, so how much do you save in actual numbers in a typical month? And is it really worth the savings to drive around like a fragile little princess when you could be screaming down the road like Mad Max instead? I can tell you right now which one is more fun.

-1, vapid.

I recommend looking at the problem differently (none / 1) (#42)
by Liar on Thu Jun 07, 2007 at 01:02:16 AM EST

It's difficult to say how much you'll save in cash because gas prices vary from month to month, city to city, country to country.

More importantly, though, this isn't an article about saving money. It's an article about getting the most from what you already pay for.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
You realize that's the same thing, right? (none / 1) (#59)
by the spins on Thu Jun 07, 2007 at 09:53:27 PM EST


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[ Parent ]

not really (none / 0) (#65)
by Liar on Fri Jun 08, 2007 at 01:40:50 AM EST

The price of gas is volatile so your savings changes. However, there's a ceiling to a car's fuel efficiency. Driving tactics can improve fuel efficiency even if your tank of gas is free.

Also, there are non-financial interests in the terms of emissions, preservation of natural resources, reducing our dependency on a foreign power, etc. So, when I talk about getting the most out of what you're already buying, I'm talking about a lot more than a narrow financial consideration.

Also, for some people who tweak out their car to get the maximum fuel efficiency, they may end up spending more on the best equipment that it offsets their cost savings.

I do find it interesting how heavily you've invested in an article you voted down.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
Read the Wash. Post article (none / 1) (#166)
by LoveAndRockets on Mon Jun 18, 2007 at 07:44:12 PM EST

about the premiere hypermiler, this guy broke the record with 150 miles/gallon. (I forget the exact amount but it was huge.)

The only thing about his driving is that it would get him yelled at in Northern California and probably killed in LA. He uses Pulse and Glide, 40 mph to 30 mph and back to 40 mph ad nauseum. Then, on hills he can get up to 100 and then takes a corner without braking to keep his momentum. He regularly conserves momentum by coasting from 25 mph to a stop with people behind him honking. (Again, in LA this will get you shot.) I would probably do a version of it but not to the extent that he does. IT also depends entirely on where you live.


[ Parent ]

The numbers are right there (none / 0) (#168)
by daborg on Wed Jun 20, 2007 at 12:36:55 PM EST

As you point out, the article states that there was a 20% mileage increase. That means your cost will be 1.2 times lower.

If you typically spend $250 per month on gas, and you improve your mileage by 20%, you will now spend $250 / 1.2 = $208 per month on gas.

See, that wasn't so hard was it?


[ Parent ]

Easier (2.60 / 5) (#11)
by j1mmy on Wed Jun 06, 2007 at 02:00:01 PM EST

Walk, fatty.

Another alternative for saving fuel (2.72 / 11) (#12)
by United Fools on Wed Jun 06, 2007 at 02:46:26 PM EST

Stay and sleep in your work place or school. Don't go home.

We are united, we are fools, and we are America!
How to drive as fun as possible (3.00 / 7) (#22)
by joto on Wed Jun 06, 2007 at 04:32:25 PM EST

I'm strange. I love to have fun. I also have an inadequate penis, so I make up for it by kicking in the macho-genes whenever I enter a motorized vehicle.

The easiest way to have more fun while driving, is to speed. This, however, is not always legal, but there are a variety of other techniques you can use to make your driving feel more like a roller-coaster-ride.

Drive at non-standard times This is self-explanatory. If you want to speed, you should avoid traffic.

Brake only at the last minute This allows you to keep top speed as long as possible. And in many cases, it's not the actual speed that makes things fun, but sharp turns, hard acceleration, and sudden breaking.

Always pass other cars Of course, passing is somewhat dangerous, so you should consider safety first! But apart from that, passing is an aggressive move that will surely help with your macho-ness.

Learn to watch the traffic lights for pedestrians. First crossing cars will get red light, then crossing pedestrians will get a red light, then pedestrians in your direction get a green light, and finally, you will get a green light. You can time this perfectly, or even better, start earlier by using e.g. the red light at crossing pedestrians as a marker for your "false start". However, watch out for red and green arrows, they can screw this pattern up.

Pay attention It's easy to get so caught up in driving that you forget about the world around you. Remember to find the right music, roll down your windows, and turn the volume up. And since you have nothing else to do while driving, now might be a good time to send some SMS-messages to your friends.

It's sometimes embarrassing how much fun we waste while driving. Most people who drive to and from work seem to use their car only for transportation. In reality, you should view the car as an extension of your own inadequate penis, and make sure that every time you drive, you are in effect masturbating this extension!

American folk science (2.81 / 11) (#26)
by the spins on Wed Jun 06, 2007 at 06:55:00 PM EST

Many of your tips are either misleading, incorrect or dubious and require further explanation.

Draft... Those enormous diesels are cutting a swaft (sic) through the air so wide that you can draft three or four car lengths behind the back and see an enormous improvement in efficiency.

This is unsafe and truckers hate it, because they cannot see you behind them. Please don't do this.

Slow Down... The speed limit is generally as fast as you should go.

Again, a safety issue -- nobody drives at the speed limit, most people drive at least 5-10 mph above it. More than this on an interstate. If you are not moving with the flow of traffic, you are a traffic hazard.

But if you're speeding egregiously, you're going to pay a premium in terms of fuel for those couple of extra seconds it shaves off your arrival time.

Actually, the efficiency is dependent on the gearing and drag characteristics of the car. One car going 55 mph can be operating at peak efficiency while another would need to be going faster to reach peak efficiency. Speed is not indicative of efficiency, so this entire bullet point is useless.

Engine control systems are designed to maintain a narrow range of fuel:air ratios during operation. As such, as more air flows through the engine, more fuel will be added to maintain the specified ratio. In most cars, the effects of throttle position and engine RPM are coupled to determine the airflow. On newer cars, as GhostofTiber mentioned, it is dependent strictly on RPM. RPM would be a much better indicator of the amount of fuel being used by the engine, though it is still not perfect.

If your foot is all the way to the floor, you're just dumping fuel into the engine while you're only going 10, 15, and 20 miles per hour. That's not efficient. Do it slowly and evenly, using a small amount of fuel when you're going slowly and less when you find yourself at your desired speed.

I would like to see your physical reasoning behind this.

Here are some of my tips to improve fuel efficiency while driving:

  • Be conscious of how you cool your car. At non-highway speeds, it is usually more efficient to cool your car by leaving the windows open, as the compressor from the air conditioner diverts power from your engine, requiring more fuel to maintain a given speed. At highway speeds, it is usually more efficient to use the air conditioner and leave the windows closed, as this reduces aerodynamic drag.
  • Read your owner's manual. It's handy to know what's in there regardless of whether you are interested in fuel efficiency. Mine happens to list the ranges of speeds at which each gear is most efficient.
  • Keep a maintenance log. Maintenance issues such as oil changes, air filter changes and fuel filter changes can make a difference in your engine's efficiency. Read your owner's manual to figure out when these need to be changed, then consult your log to figure out if maintenance is due.
  • Keep your tires pressurized. Cars usually have a sticker somewhere inside the driver's side door frame that indicates the proper pressures that your front and rear tires should be inflated to. Under inflation can cause additional rolling resistance, lowering your fuel economy. Note that these figures are indicated for cold tires, i.e. tires that have not been driven on in the past few hours. This is important.
  • Remove excess weight. Increased downforce (whether induced by weight or aerodynamics) leads to increased rolling friction. If you're carrying around a ton of stuff in your trunk for no good reason, remove it. There's no need to go overboard with this one, though, since its effects are small and it's really something you look at once you've done everything else.
  • Remove roof racks and other drag-causing structures. If you have roof racks on your car, take them off when you're not using them. They cause aerodynamic drag, especially at highway speeds. The same can be said of other cargo carriers mounted on other exterior parts of the car.

Most of these are basically guided by two principles: minimize your aerodynamic drag, and maintain your engine. If you keep these in mind, you may spot things in your driving that I have forgotten to mention here.

Overall, I am disappointed in this article, as it is not a serious analysis of fuel efficiency and does not provide one with the analytical tools necessary to understand the physical processes at work and determine new courses of action that may lead to additional increases in efficiency. K5 is a community of technically-minded individuals and tinkerers, and as such would benefit from a technical treatment. I may write such an article in the future, provided this one does not get posted.

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couple of things (none / 1) (#27)
by Liar on Wed Jun 06, 2007 at 07:20:36 PM EST

1) the magic of being in the edit queue is that this article can still change. Me being at work at the moment, I'm only doing superficial changes; the heavy lifting I'll do when I get home. So, I will be adopting some of your suggestions to make this more technically minded. While most here are technically minded, that's not the audience I was trying to speak to, so I was keeping it generic and basic. Still, it seems that the gearheads want the numbers so I plan on adding it.

2) thank you for the additional suggestions on how to improve efficiency.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
oh also (none / 0) (#28)
by Liar on Wed Jun 06, 2007 at 07:28:53 PM EST

"Actually, the efficiency is dependent on the gearing and drag characteristics of the car." and I'd add the driver's style.

Most people want easy tips on how to get something done. Keeping a log, monitoring tire air pressure, removing roof-racks, absolutely those make a difference. I'm trying to appeal to the lazy folk who won't do that. Changing a driving style takes no extra effort and it does improve efficiency.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
You would like to see my physical reasoning behind (1.50 / 2) (#30)
by WonderJoust on Wed Jun 06, 2007 at 07:45:21 PM EST

If your foot is all the way to the floor, you're just dumping fuel into the engine while you're only going 10, 15, and 20 miles per hour. That's not efficient. Do it slowly and evenly, using a small amount of fuel when you're going slowly and less when you find yourself at your desired speed.

I would like to see your physical reasoning behind this.

More (read:faster) acceleration requires more force requires more fuel.

LOOK I LEARNED PHYZIKS!

On a side note, remember when we used to b0mb dakini? Those were the days.

_________________________________
i like your style: bitter, without being a complete cunt about it.
-birds ate my face
[ Parent ]

That's specious reasoning (3.00 / 1) (#33)
by the spins on Wed Jun 06, 2007 at 08:15:19 PM EST

Neglecting friction, you do the same amount of work in moving a mass a given distance irrespective of the time taken. When figuring in rolling friction and drag, the differences should be negligible, as you are starting at the same speed and accelerating to the same speed. Where do the inefficiencies come from?

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[ Parent ]

You're assuming a perfect system (none / 0) (#36)
by WonderJoust on Wed Jun 06, 2007 at 09:29:26 PM EST

Which we don't have. More accel = higher RPMs = more gas lost.

Yes, if we could harness every little bit of energy from the burning fuel, it wouldn't matter. Unfortunately, we all live in this place called 'Reality' not 'perfect physics land'.

It's hard for me to rebuke obviously wrong notions without sounding condescending but I want you to know I tried.

Ok, not too hard.

Also, my first equation was incorrect in a perfect world. Shoot me.

_________________________________
i like your style: bitter, without being a complete cunt about it.
-birds ate my face
[ Parent ]

Uh no (3.00 / 3) (#40)
by the spins on Wed Jun 06, 2007 at 10:07:32 PM EST

One can accelerate at full throttle without revving the engine high with an aggressive shifting regime. If you're going to be a condescending cockbag, you'd better make sure you're right before you post.

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[ Parent ]

How, exactly, do you do that? (none / 0) (#52)
by WonderJoust on Thu Jun 07, 2007 at 07:13:27 PM EST

If your RPMs are low, you're accelerating more slowly no matter how aggressive you shift. By this strategem, you'd basically be starting from a crawl on every gear.

Not to mention your clutch and synchros are going to hate you.

I understand what you're getting at, but it just doesn't work. I don't understand enough about mechanics/physics/math/children to explain it any better so I'm going to stop trying now.

Ta ta.

_________________________________
i like your style: bitter, without being a complete cunt about it.
-birds ate my face
[ Parent ]

it depends on your torque curve (3.00 / 3) (#55)
by the spins on Thu Jun 07, 2007 at 08:24:55 PM EST

do you understand what a torque curve is?

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[ Parent ]

Yes. /nt (1.50 / 1) (#58)
by WonderJoust on Thu Jun 07, 2007 at 08:51:32 PM EST


_________________________________
i like your style: bitter, without being a complete cunt about it.
-birds ate my face
[ Parent ]

allow me (none / 1) (#115)
by IncubatedVitamin on Mon Jun 11, 2007 at 01:07:27 AM EST

when you bog your engine in 3rd gear at 1500rpm, you are basically maxing out the amount of gas your engine will accept without going rich. you do this for a longer period of time.

when you flog your engine in 1st gear at 4000rpm, the same effect happens, using a bit more gas, but for a shorter period of time. i call this the flog and fly method.

"blah blah blah you're not conserving gas"

my car computer has confirmed that i get 8mpg for 10 seconds of acceleration compared to 15mpg for 30 seconds. my overall gas consumption has confirmed an increase in average fuel effeciency at 2mpg when i use the flog and fly method. do you have any data to backup your points?

[ Parent ]
actually... (none / 0) (#39)
by Liar on Wed Jun 06, 2007 at 09:55:23 PM EST

there's a group called hypermilers and this is uniformly the recommended method for starting. Considering these guys get (on average) 60 mpg and in competition get over 110 mpg, I'll trust them.

If you have a fuel consumption meter, try this out. From a dead stop, haul ass. Generally, you'll get about 4mpg or less for the entire burn. Now, try starting slowly. In my automatic, if I let it coast on its own and then engage after a second of forward motion (since automatics do this), and then evenly accelerate, I generally start out at 14 mpg and it only improves from there. In a stick shift, you'll be able to do the entire operation more efficiently and consequently with better fuel economy.

Anyway, I'm going to provide links to various forums where people discuss hypermiling (as well as a few others), but this is one piece of advice almost everyone is uniform on giving.


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
energy, force, work, power (none / 1) (#94)
by Entendre Entendre on Sat Jun 09, 2007 at 02:16:35 AM EST

Doing the same work over less time (i.e. accelerating more quickly) requires more power. Generating more power means burning more fuel.

--
Reduce firearm violence: aim carefully.
[ Parent ]

Neglecting friction, yep. (3.00 / 1) (#100)
by garote on Sat Jun 09, 2007 at 10:18:40 PM EST

However, in this forum, we're all driving gasoline-powered internal combustion engines attached to drive-trains of varying (but universally shitty) quality.  Harder acceleration applies more pressure to every single piece of that system, from piston chamber walls to fluid-filled rear differentials.

Not a LOT more, of course.  But more nonetheless.  No one is claiming you can get massive fuel savings from a slow start off a stop light.  The original author didn't; I'm not.

When you're at a stoplight, YOU ARE STOPPED.  You must pass up through the bottom of that first gear no matter what.  Your only choice is whether you do that fast or slow.  This is not a matter of efficiency at some RPMs of the gears in the transmission, this is a matter of the torque that must be applied by the engine to ACCELERATE, which is obviously more torque than must be applied to maintain speed as this or that 'most efficient' RPM.

Hot-rodding off a stoplight can easily triple the pressure involved, and the torque required, as well as the friction to be overcome.  You may think that you can eliminate this by shifting differently - but such actions are moot: you're thinking beyond first gear.  We're talking about first gear here.  Tripling the amount of torque you demand while spinning up through the RPMs of first gear can only have a negative effect on fuel efficiency, in any but the most oddly calibrated engine.

If you like, you can apply this principle to all acceleration across all gears:  The faster you do it, the narrower your 'peak efficiency' range becomes, no matter how you shift.

[ Parent ]

Thank you (none / 0) (#106)
by the spins on Sun Jun 10, 2007 at 10:21:02 AM EST

That is a very good explanation.

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[ Parent ]

More physical Reasoning (none / 0) (#44)
by brain in a jar on Thu Jun 07, 2007 at 06:27:17 AM EST

I assume that if you have your foot flat to the floor it is going to shift the fuel:air ratio in the direction of more fuel less air. This will lead to incomplete combustion with more chemical energy in the form of unburnt hydrocarbons and carbon monoxide (which is also flammable) going to waste.

Although this all rests on the assumption that flooring the pedal shifts the fuel air ratio significantly and I don't know this for a fact.


Life is too important, to be taken entirely seriously.
[ Parent ]

dubious assumption, right conclusion (none / 1) (#95)
by Entendre Entendre on Sat Jun 09, 2007 at 02:32:49 AM EST

Modern cars are capable of running a pretty constant air/fuel ratio using feedback from oxygen sensors in the exhaust stream. Your foot controls the throttle opening, and the engine control unit squirts in whatever amount of fuel it deems appropriate.

At cruise, the ECU will aim for a chemically balance AFR. However if you're asking for lots of power the ECU is going to run a bit richer (more fuel, per unit of air). With a turbocharged car, it's going to run a lot richer, for a bunch of reasons I won't go into here. If you're really concerned about mileage, you probably don't have a turbocharger, because all they do is help you burn more fuel in less time by cramming more air into the motor to combust with said fuel. And when not helping you burn loads of extra fuel, they restrict exhaust flow a bit, making the engine slightly less efficient.

But anywya, the key reason for accelerating gently is that getting for point A to point B in less time requires more energy (same work in less time requires more power), and engines make energy by burning fuel. Accelerating gently means using less power (and thus less fuel) to get the same work done (i.e. to get you to your destination).

--
Reduce firearm violence: aim carefully.
[ Parent ]

hmm (none / 0) (#108)
by tetsuwan on Sun Jun 10, 2007 at 03:47:14 PM EST

Turbos can actually be good for fuel efficiency under certain circumstances. And all new diesel engines are turbo-charged, but AFAIK they work differently.

Your second point holds, but the (ideal) work needed to get to a certain speed is always the same, but if you accelerate harder you will also accelerate in a shorter distance.

The bigger issue is that accelerating forces your engine out of equilibrium conditions, and it cannot be designed to accelerate efficiently without sacrificing performance and changing the general behavior.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

no free lunch (none / 0) (#110)
by Entendre Entendre on Sun Jun 10, 2007 at 05:14:14 PM EST

but if you accelerate harder you will also accelerate in a shorter distance Yeah, but still, you don't break even. It would be nice if you could get to your destination in less time without burning more fuel, but it doesn't work that way.

The big issue is that acceleration is more expensive (in terms of fuel consumption) than you think.

Those turbo diesels would get even more efficient if they weren't turbocharged. But the performance wouldn't be acceptable. Adding a turbocharger does not yield an efficiency increase. It costs less than increasing displacement to get an equivalent performance improvement, but it still costs.

--
Reduce firearm violence: aim carefully.
[ Parent ]

double negation (none / 0) (#111)
by tetsuwan on Sun Jun 10, 2007 at 05:55:10 PM EST

My point is actually that if you accelerate faster, you will have gone a shorter distance by the time you reach your cruising speed, thus expending using the same work to cover a smaller distance ...

My more serious comments are posted above.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

oh and (none / 0) (#114)
by tetsuwan on Sun Jun 10, 2007 at 06:38:38 PM EST

I'm not sure that you're correct about the diesels: the VW Lupo 3L TDI did 80 mpg. Even the diesel version of SMART uses a turbo diesel. Do you mean that a regular diesel is more efficient but too heavy?

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

More efficient than what? (none / 0) (#116)
by Entendre Entendre on Mon Jun 11, 2007 at 01:12:05 AM EST

There's two ways to compare:

A: Compare against the same engine with the turbocharger removed. You'd see even better mileage. But the resulting engine would also be less powerful. Probably intolerably gutless. So the manufacturers sacrifice some efficiency to give small engines tolerable performance. It's a reasonable (and thus popular) tradeoff.

B: Compare against a naturally aspirated engine that makes equivalent power. The larger NA engine would indeed be less efficient than the smaller-but-turbocharged engine.

So it depends on which comparison you consider most appropriate.

--
Reduce firearm violence: aim carefully.
[ Parent ]

Now you're making a strange point (none / 0) (#117)
by tetsuwan on Mon Jun 11, 2007 at 01:25:48 AM EST

If you use a turbo charger to go from 80 to 120 hp, that would mean increasing the potential to burn fuel. Here we agree. But TDIs can be made with a great range of powers, so the reasonable comparison would be between a 80 hp TDI and an 80 hp "vanilla" diesel engine. In this case I'd say the TDI wins.

My only gripe with the TDIs is the $2000 extra bill the come with. And the word is that they are powerless before the turbo sets in.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

far as I can tell.... (none / 0) (#157)
by Entendre Entendre on Fri Jun 15, 2007 at 01:13:28 AM EST

...you just said the same thing I said, only with different words.

--
Reduce firearm violence: aim carefully.
[ Parent ]

Not good reasoning (2.00 / 1) (#57)
by dissonant on Thu Jun 07, 2007 at 08:38:53 PM EST

While you're definitely going to use more fuel under hard acceleration, you're using more fuel for a much shorter time.  If you accelerate slowly, you still using more fuel than you would at a steady speed, and you using it over a much longer period of time.

I know on my bike, if I pin the throttle and accelerate to cruising speed as quickly as possible, I tend to get more out of a tank than if I put around up to speed.  I also smile more.

[ Parent ]

+1FP (3.00 / 1) (#37)
by insomnyuk on Wed Jun 06, 2007 at 09:32:07 PM EST



---
"There is only one honest impulse at the bottom of Puritanism, and that is the impulse to punish the man with a superior capacity for happiness." - H.L. Mencken
[ Parent ]
Engine RPM != fuel flow (none / 0) (#96)
by nightfire on Sat Jun 09, 2007 at 02:53:33 PM EST

Engine control systems are designed to maintain a narrow range of fuel:air ratios during operation. As such, as more air flows through the engine, more fuel will be added to maintain the specified ratio. In most cars, the effects of throttle position and engine RPM are coupled to determine the airflow. On newer cars, as GhostofTiber mentioned, it is dependent strictly on RPM. RPM would be a much better indicator of the amount of fuel being used by the engine, though it is still not perfect.

Fuel flow (and hence A:F ratio) is determined by the intake airflow sensor, not the engine speed or throttle position (though those inputs are also considered).

The crank speed itself can never be used to determine appropriate fuel flow.

When the throttle is closed but the engine is at high revs (ie. engine braking), airflow and fuel are restricted.  An increased fuel flow would cause a rich burn and spew unburned hydrocarbons out the tail pipe.  When the throttle is wide open and engine speed low (hard acceleration), there is still a large amount of air entering the engine, and hence a large amount of fuel is added.  As the engine speed increases under WOT (wide open throttle), the change in air and fuel flow is somewhat linear WRT the engine speed, but still primarily determined by the mass airflow (or equivalent) sensor.

[ Parent ]

Yes. (none / 0) (#97)
by the spins on Sat Jun 09, 2007 at 03:36:06 PM EST

Of course I know that the ECU uses a mass flow sensor to determine appropriate fuel input levels. However, in terms of instrumentation available to drivers of factory-stock cars without mileage readouts, RPM and throttle position allow one to make a rough approximation.

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[ Parent ]

mmmmyeah (none / 1) (#99)
by garote on Sat Jun 09, 2007 at 08:46:57 PM EST

Your advice is good but your tone is preachy.  Do you really need the "physical reasoning" behind accelerating a car slowly off a stop light??

Pick up a tennis racket and move it slowly back and forth in the air ten times.  Now swing it, really hard, ten times.  QED.  You figure it out.

Draft: You can get the benefit of this by being well enough behind a truck so that you can see its side mirrors.  As the author states.  You must have missed that.

Speed limit:  Any road with more than two lanes means YOU ARE the flow of traffic.  Get in the rightmost lane you possibly can, change lanes preemptively, and you will have absolutely NO problem going 55mph.

If you call people driving 55 in those conditions a "hazard", it is you who are the hazard.  I hate middle-lane campers as much as the next guy - but I still recognize that, when I head over highway 17 doing 70mph, I am the law-breaker, the endangerer, and the waster of fuel.  So should you.

[ Parent ]

Um... (none / 0) (#140)
by DavidTC on Tue Jun 12, 2007 at 02:04:59 PM EST

Draft... Those enormous diesels are cutting a swaft (sic) through the air so wide that you can draft three or four car lengths behind the back and see an enormous improvement in efficiency.

This is unsafe and truckers hate it, because they cannot see you behind them. Please don't do this.

Why the fuck would truckers need to see cars behind them? Do they have some magically 'flip all forward momentum into reverse momentum' button I am unaware of? Or maybe sometimes they like to release their trailer while driving down the highway?

Trucks take about twice as long to stop as cars, which is why people almost never rear-end them, and why they often read-end people, or jackknife while trying to avoid hitting people. It is much safer following a truck at a certain distance than it would be following a car at the same distance. If they jackknife, you're in trouble, but you'd be in just as much trouble if you were next to them.

Now, I disagree with the GP that you can actually 'draft' a truck from three or four car lengths away and have any gain...you'd have to get way too close to do that to be safe. But that has nothing to do with the fact that truck drivers can't see you, it has to do with the fact you couldn't stop in time.

Drivers, in general, have no need to see directly behind themselves, because they can't do anything about cars back there. In some emergencies they possibly could move out of the way, but that's just tempting fate as the car behind them could realize they're about to hit you and swerve in the same direction.

Plus, they don't even look. Drivers use middle rear-view mirrors for two things: Backing, and seeing a long-distance view of the road behind them, including other lanes. They don't sit there and watch for vehicles behind them that they may need to dodge, even if that was physically possible for them to accomplish, which it certainly is not for tractor-trailer drivers.

-David T. C.
Yes, my email address is real.
[ Parent ]

Funny you should mention that... (none / 0) (#143)
by bgarcia on Tue Jun 12, 2007 at 03:04:23 PM EST

Drivers, in general, have no need to see directly behind themselves, because they can't do anything about cars back there. In some emergencies they possibly could move out of the way, but that's just tempting fate as the car behind them could realize they're about to hit you and swerve in the same direction.
Just yesterday, I used my rear-view mirror to avoid an accident on the highway.

The U.S. Open is in my neck-of-the-woods, and some maintenance-only on-ramps where being used by busses taking people to and from the Open. They had signs warning people to get in the left lane, so I did once someone finished passing me. But the lady behind him was coming up fast, and just as I was switching lanes, I noticed her looking sideways at the "warning sign". While still gaining on me at a 10-20mph differential. I ended up swerving back into the slow lane when I was halfway merged.

[ Parent ]

That only worked... (none / 0) (#148)
by DavidTC on Tue Jun 12, 2007 at 09:08:33 PM EST

...because you didn't use your side mirrors in the first place. :)

But, no, I'm not saying that, under no circumstances, rear-view mirrors aren't useful. I was actually saying that, under almost no circumstances, knowing someone is behind you is not useful.

You actually brought up what is probably the sole exception to that, when you have just changed lanes and hence can safely change back, but notice it wasn't due to someone following too closely, so is not really applicable to the 'It doesn't matter if the driver you're following can see you or not' point I was trying to make.

Incidentally, speaking of signs causing accidents, near where I am, there is a sign warning people to pay attention while driving, because the road is a high traffic area. It is a large green three feet wide and two feet tall sign, with at least 30 white words on it. At least, 'slow down, high traffic' is the gist I get from scanning it as I go past, because there's no way in hell anyone can actually read it.

No, I'm not kidding or exaggerating, someone actually through that was a useful idea. It is, indeed, in a place extremely likely to cause accidents if someone were to slow down or swerve, say from, I dunno, reading six lines of white text on a green background. I should take a picture of it some day. (I assure you, I would be smart enough to park and walk up to it.) Then I should hunt down the person who thought it up and sterilize them for the good of the human race.

-David T. C.
Yes, my email address is real.
[ Parent ]

Bull (none / 0) (#155)
by bgarcia on Thu Jun 14, 2007 at 07:52:18 AM EST

...because you didn't use your side mirrors in the first place. :)
Bullocks. She was well behind me when I merged. She just kept looking at the spectacle on the side of the road instead of noticing that the cars in front of her were merging & slowing down.

Anyhow, I agree with the premise that the rear-view mirror is rarely useful, but I thought it was funny that I had just used it to avoid an accident.

The only other case I can think of where watching behind you is necessary for safety is when you're in a long line of cars stopped at a light, around a curve with a hill that doesn't let you see around the curve. I try to stay back a few car lengths and watch the mirror in case someone comes whipping around the curve not expecting the line of cars waiting at the light to be that long. My hope is that the idiot will finally slam on the breaks, and I'll have a little bit of room to move up to avoid an accident.

[ Parent ]

christ, you're a mirror-backer, too. (none / 0) (#146)
by the spins on Tue Jun 12, 2007 at 08:27:27 PM EST

stay off my roadways, you bellicose asshole.

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[ Parent ]

No. (1.50 / 1) (#149)
by DavidTC on Tue Jun 12, 2007 at 09:13:50 PM EST

People don't use their mirror when backing on the roads or long distances. They turn around and back.

They use their mirror for backing when they need to watch the side mirrors too, like if they need to back in very tight spaces.

I don't know where you go 'A thing a rear view mirror is used for is backing' and turned it into 'I always back using my rear view mirror'. The fact that backing is normally accomplished by turning around does not mean that rear view mirrors should not, in any circumstances, be used while backing.

Jeez, it's like I said that brown sugar was used for cooking, and you leap in and said 'christ, you don't know that when a recipe calls for sugar, it means white sugar. stay away from my food, you bellicose asshole.'

I know how to back a damn car, and I, like most other people who have operated a one, know at times you do indeed need the middle, and side, mirrors, to back somewhere, despite the fact you normally back by turning around to the right in your seat.

Incidentally, I believe you need to look up the definition of 'bellicose', because it means how you were behaving, not me.

-David T. C.
Yes, my email address is real.
[ Parent ]

i appreciate obsessive compulsive disorder (2.50 / 6) (#31)
by circletimessquare on Wed Jun 06, 2007 at 08:05:52 PM EST

+1 fp

The tigers of wrath are wiser than the horses of instruction.

This is a disorder Al Gore wants everyone to have (2.20 / 5) (#32)
by United Fools on Wed Jun 06, 2007 at 08:14:11 PM EST


We are united, we are fools, and we are America!
[ Parent ]
Thank you, David Brooks. (2.25 / 4) (#34)
by the spins on Wed Jun 06, 2007 at 08:16:11 PM EST


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[ Parent ]

so who are you really, are you rusty? nt (1.00 / 2) (#35)
by circletimessquare on Wed Jun 06, 2007 at 08:16:19 PM EST



The tigers of wrath are wiser than the horses of instruction.

[ Parent ]
Not in America, Buddy! (2.66 / 9) (#41)
by Peahippo on Wed Jun 06, 2007 at 10:38:59 PM EST

I hope y'all realize that by following at last two of these points, the rest of the Average American Assholes behind you will essentially attempt to kill you one of these days, by being "too slow". If you accelerate sanely, the jackrabbits behind you will be pissed off. If you drive slowly, the speedsters behind you will be pissed off. America is the land of fast starts, high speed, and massive braking. That's how we blow through a lot of gasoline and have a lot of accidents. Since we're better than the rest of the world, that's perfectly OK, right? However, we don't need some Socialists trying to save on gas, crawling out of intersections after the light change and be-bopping down the road like a Sunday driver.

To avoid road rage, eventually you'll have to conform. Slam that pedal upon starts and stops, and follow the rest of the traffic when it goes a minimum of 10MPH over the speed limit. By not driving an SUV, we already know you have a tiny cock, don't get laid and work a low-paying loser job with no future; don't embarrass yourself further with "gas conservation" techniques like some fuckin' Eurofag.


right (none / 1) (#50)
by khallow on Thu Jun 07, 2007 at 12:25:00 PM EST

You usually troll better than this.

PS, what country do you actually live in?

Stating the obvious since 1969.
[ Parent ]

Firstly, it wasn't a troll. (2.40 / 5) (#64)
by Peahippo on Fri Jun 08, 2007 at 01:38:01 AM EST

Secondly, you must have a few problems with reading comprehension, to wit:

"the rest of the Average American Assholes behind you"

... is a clear statement that I'm in America since the "rest of" some other Americans are behind ME-IN-MY-EXPERIENCE screaming horn-ifically about my smooth and slow acceleration.

For such an allegedly highly-educated class, you yuppies really don't get it with your own society. Driving, accelerating and braking slower on American roads is very much demonized by the average driver. This is true since the average American driver is a gasoline-and-lard supported asshole who cares about nobody but himself on the road.

Since I drive like a Eurofag myself, I see this sort of thing often enough. But according to your implication, I must have imagined it all. So. You've been stating the obvious since 1969? Pardon me when I do the same: In this instance, kh, screw you. Bloodily.


[ Parent ]
You're wrong (none / 0) (#90)
by stevie on Fri Jun 08, 2007 at 10:23:10 PM EST

Most places have higher speed limits than the US. It's 130 kph or about 80 mph on highways here in a European country but it's not uncommon to see people go 160 kph or 100 mph (there's even one stretch of highway where that's the official speed limit).

And have you ever heard of a place called Germany?

Your post was fun but dude, check your facts.

[ Parent ]

It's Called Critical Thinking (1.50 / 4) (#93)
by Peahippo on Sat Jun 09, 2007 at 01:46:10 AM EST

You might want to give it a try sometime.

Firstly, American is a land of ILLEGAL high speed. We generally go faster than our speed limits indicate. As it happens, I commonly see people going at least 10MPH over on the near highways. That's a 75MPH effective speed limit there, good buddy! Pretty close to your lovingly stated 80MPH stat, isn't it? 55-65 limits are a joke and few people follow them. And that's just on city-hugging stretches. The longer ranges have people going at least 80, sometimes 90. And this speediness extends down the limit ranges, so people commonly go 35+ on roads posted for 25.

The natural conclusion is that Americans are leadfoots and their 'low' speed limits place that in high relief since the limits are only obeyed plainly by a minority of the populace. Everyone else speeds, and I'd say anecdotally that the top 25% think they live in these European areas you tout.

Now, if people in European lands also speed ILLEGALLY with equal ardor, you might have an argument. About the only trend I've seen in Europe is not going too fast at high speeds, but in being too careless at low ones.

Secondly, Germany has the Autobahn, flyin' with aerodynamic cars which wholly fail to resemble air-pushing SUVs. The Autobahn isn't as pervasive as the American highway system. So, in an absolute sense of scale, you fail it. A set of speedy Germans on their Autobahn with fuel-efficient cars does NOT a speedy nation make. What I recall from my German classes is that the Autobahn is the exception and speed limits elsewhere in (i.e. most of) the country are comparable to the USA.

Thirdly, my posts are indeed fun, and it's kind of you to notice, but they also check out factually. It gets even better than that, too, since if you can prove me wrong (admittedly, a rare thing for K5) then I'll accordingly and sanely change my opinion ... so that I'll be right again, which is how it should be.


[ Parent ]
Autobahn full of BMWs going at 200+km/h ~125mp/h (none / 0) (#118)
by drx on Mon Jun 11, 2007 at 01:48:59 AM EST

Also, of course Daimler, Porsche, BMW, Audi etc build SUVs and people happily drive them in Germany as well -- even using them for much shorter distances than the typical USA resident that needs to drive many kilometers to the next supermarket or to work.

Cars just suck everywhere.

[ Parent ]

I'd Really Like to Know (1.00 / 3) (#119)
by Peahippo on Mon Jun 11, 2007 at 06:26:11 AM EST

Is the Autobahn today really filled with SUVs, considering the price of gas in Germany? Do Germans really drive as much as Americans, with the much greater availability of public transit in Germany? I find myself doubting all that, but you can help me along by quoting the SUV stats for Germany, if you'd be so kind. The last time I looked (2002?), there was 1 SUV for every 5 drivers in America.

You're right that cars basically suck in most places on Earth. If VW can build a prototype that gets 240MPG -- and they did -- it's not difficult to imagine that they could create a production line for a modest run of a 120MPG derivative of that model. You could get over 45MPG easily in a small Toyota model car in the early 1990s. All that efficiency progress was wiped out and now we have to pretend the Prius is some sort of fabulous advance. Bullshit.


[ Parent ]
I will have none of it! (none / 0) (#177)
by transport on Wed Aug 01, 2007 at 03:44:34 AM EST

To avoid road rage, eventually you'll have to conform.

I swear, this has got to be the first time ever on kuro5hin that I've seen an american suggest that other americans should just bow to the wish of others.

[ Parent ]

I have had friends like you (1.50 / 4) (#45)
by Egil Skallagrimson on Thu Jun 07, 2007 at 10:35:35 AM EST

I think it's hilarious that they ossessively measure everything, but I'm always interested in the results. Like, really interested. Like, phone them the next day to get updates interested.

However, any time I've thought of doing the same thing, I immediately, thought "Why the hell for?"

----------------

Enterobacteria phage T2 is a virulent bacteriophage of the T4-like viruses genus, in the family Myoviridae. It infects E. coli and is the best known of the T-even phages. Its virion contains linear double-stranded DNA, terminally redundant and circularly permuted.

Toys help (none / 1) (#47)
by Liar on Thu Jun 07, 2007 at 10:44:27 AM EST

GPS receivers, fuel consumption readouts... if you have a toy, you want to put it to use, especially if you think of it as a toy and not merely as a device.

Though, I have counted the number of steps between me and the photocopier. I have two routes and one route is two steps shorter (35 compared to 37).


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
Constant speed helps traffic too (3.00 / 2) (#51)
by rpresser on Thu Jun 07, 2007 at 03:27:15 PM EST

(Of course it has to be the right constant speed ...) There's some interesting information about traffic jams here.  When you're stuck in a stop/start line of half a mile of angry people waiting, it feels better to be moving continuously at 1 mph than waiting 5 minutes, going 500 feet at 10 mph, waiting another 5 minutes....  A huge gap may open in front of you and opportunists will cut in, but so what? you're still moving.
------------
"In terms of both hyperbolic overreaching and eventual wrongness, the Permanent [Republican] Majority has set a new, and truly difficult to beat, standard." --rusty
Throttle (Accelerator Pedal) (none / 1) (#53)
by prometheus on Thu Jun 07, 2007 at 07:27:43 PM EST

In most cars this pedal doesn't control the fuel supply to the engine directly.  Rather, it allows more air into the firing chambers, which will cause the engine control computer to let in more fuel up to the point that no more will burn.  If you open the throttle all the way, you will use the same amount of fuel as if you follow the torque curve of the engine.

Of course, opening it all the way will burn as much fuel as can be burned, and likely will be more than if you manage your acceleration better than the people jumping off the line every time the light turns green...
--
<omnifarad> We've got a guy killing people in DC without regard for his astro van's horrible fuel economy

*most* cars? (none / 1) (#54)
by the spins on Thu Jun 07, 2007 at 08:23:06 PM EST

are you making exceptions for cars powered by gas turbines or something?

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[ Parent ]

Full throttle enrichment (none / 1) (#101)
by Pholostan on Sun Jun 10, 2007 at 04:26:10 AM EST

All gasoline cars have it. This means that then you put the pedal to the metal, especially on low rpms, the engine gets more fuel than it can burn. Why? To avoid detonation. Under heavy load, detonation is not something you want in your otto cycle engine. Thus flooring it will always burn more fuel than more modest acceleration. And cause excessive wear and tear etc...

- And blood tears I cry Endless grief remained inside
[ Parent ]
A much more fun way to save gas... (3.00 / 5) (#56)
by dissonant on Thu Jun 07, 2007 at 08:29:21 PM EST

...Get a vehicle with two less wheels and actually use it as your primary vehicle, rain or shine.  If you live in a place with snow and ice in the Winter, this is obviously a seasonal solution.

I get a little over 50mpg on average on my DL650, and I'm not being easy on the throttle.  If I really try to stretch a tank, I can get a little over 60mpg.  All this economy, and I can accelerate to 60 within a hair of 4 seconds, and run a quarter mile in under 13 seconds.  I can also out brake and out maneuver the vast majority of cars, and fit into places cars can't.   It makes parking much easier.

Granted, it takes more coordination and concentration to ride a moto, and the consequences of screwing up can be harsh.  OTOH, the added mobility and smaller size allows you to avoid accidents far better than a car, provided you're alert and skilled enough.  I can think of several situations where I would have been hit by another vehicle if I had been driving a car.

I can also say that for me at least, I feel much better when I commute on the bike.  It's good for the soul to be outside and absorbing the sights and sounds and smells, and meeting the elements head on, whether it's enjoying a pleasant spring day or enduring a freezing cold night.  I arrive to my destination invigorated, alert, and relaxed.

If transporting one or two people is primary use (3.00 / 3) (#72)
by rpresser on Fri Jun 08, 2007 at 10:00:59 AM EST

then a two-wheeled vehicle makes sense and will save fuel.  But if you frequently have more people to transport, or frequently need to carry cargo, it becomes less sensible.
------------
"In terms of both hyperbolic overreaching and eventual wrongness, the Permanent [Republican] Majority has set a new, and truly difficult to beat, standard." --rusty
[ Parent ]
Cargo is not a problem. (none / 0) (#79)
by dissonant on Fri Jun 08, 2007 at 04:41:37 PM EST

With a large duffel bag and some creative bungie cord use, I can carry 12 bags of groceries.  Or 6 bags of groceries and a 50 lbs bag of dog food for my boxer.

A single passenger isn't a problem either, though obviously you can't carry as much stuff with another person on the bike.

[ Parent ]

True, but for whom? (none / 1) (#161)
by Kadin2048 on Sat Jun 16, 2007 at 05:31:19 PM EST

This is true -- but I'd wager that the vast majority of passenger cars in the U.S. travel most of their miles with only a single person in them. Many people seem to have rather large, five- or seven-passenger cars, "just in case" they need to carry a few people, but don't ever use the extra space more than a few times a year.

Not saying that's your situation necessarily, but it certainly seems common. If everyone were packing three or four (or, hell, even two) people into their cars during the morning commute, that would probably have a greater effect than all the "hypermiler" techniques, even used on hybrid engines.

[ Parent ]

for maximum fun (3.00 / 3) (#78)
by raduga on Fri Jun 08, 2007 at 12:52:07 PM EST

and lollocity, ditch the second wheel.

[ Parent ]
With proper use of the throttle, clutch... (3.00 / 4) (#80)
by dissonant on Fri Jun 08, 2007 at 04:44:20 PM EST

...and depending on my current speed, the rear brake, my motorcycle can transform into a unicycle.  

[ Parent ]
You must live in one of those sunny states... (none / 1) (#142)
by bgarcia on Tue Jun 12, 2007 at 02:55:29 PM EST

...or you don't care about getting wet.

[ Parent ]
We get plenty of rain... (none / 0) (#145)
by dissonant on Tue Jun 12, 2007 at 07:45:09 PM EST

...I say as we're in the midst of the worst drought I can remember.

It's called rain gear.  Costs about $50 or so, and depending on the make you either put it on over or under your usual motorcycle armor.  That, or most of the colder weather riding gear is water proof to begin with, and you don't need rain gear.  I can understand the confusion though, most weekend warrior types don't even have proper armor, let alone rain gear - they only ride when it's sunny and 70 degrees, after all.

It can be a monsoon out, but with the right gear, I'll still get where I'm going and arrive bone dry.

[ Parent ]

Use public transportation (1.33 / 6) (#68)
by bob6 on Fri Jun 08, 2007 at 04:31:40 AM EST

That would beat any dull microlitre economy.

Cheers.
or use your bike to work... (none / 1) (#69)
by mirko on Fri Jun 08, 2007 at 06:16:46 AM EST

http://www.biketowork.ch
--
Finally I managed to make the decision that I would work on it. - MDC
we had to huddle together - trane
[ Parent ]
deutsch | franšais | italiano (none / 0) (#163)
by pin0cchio on Sun Jun 17, 2007 at 11:11:12 AM EST

From your link: "deutsch | franšais | italiano"

Do you know of a resource of comparable quality for people who took english | espa˝ol in high school?
lj65
[ Parent ]

Outside of the few cities ... (1.80 / 5) (#70)
by Peahippo on Fri Jun 08, 2007 at 06:55:09 AM EST

... which have train-based public transit, PT is a joke in America since it takes you enormous amounts of time to get to where you're going, even assuming it gets there in the first place.

In my Rust Belt city, it commonly takes over an hour to get to where a car can take you in 15 minutes. Pure redevelopment hopes (i.e. FEARS) demanded that the system be hub-centric around the downtown that only a minority wants to go to. Riding the system usually demands you go downtown first, before arriving at your destination. On top of that, the system resists innovation since it's staffed with cronies and pension-sitters, and finally it depends upon subsidy from property taxes anyway. In short, it's the worst possible solution for PT. So most people rely on cars.

I suspect that my local PT scheme has been repeated many times across America for the same stupid reasons.


[ Parent ]
If you have crappy PT planning... (none / 0) (#173)
by Vesperto on Sun Jul 01, 2007 at 09:15:21 PM EST

...you have crappy PT. Most cities here have regular PT, mine has better-than-eaverage. I only need to use a car at night, when PT gets down to crappy American levels and all buses do go downtown first (and it's actually a want, not a need). But during the day? I can be everywhere in 30m to 1h - that doesn't bother me. I work and study and don't own a car. Nor do i want to, too much expense. If i ever do buy one, it'll be a hybrid.
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[ Parent ]
I live walking distance to a rail station... (2.00 / 3) (#82)
by dissonant on Fri Jun 08, 2007 at 05:50:02 PM EST

...and my office is right next to another one.  I'd use it if I worked a 9-5 shift, but since I work later into the night, it's not practical.

The trains are still running when I get off work, but not nearly as often, and not on the same route, which forces me to make a transfer and wait another 30-45 minutes for the connecting train.  If I ride the motorcycle in, I can be home in 20 minutes, if I take the train, it'll be at least 2 hours.

[ Parent ]

The buses stop running (none / 1) (#162)
by pin0cchio on Sun Jun 17, 2007 at 11:09:15 AM EST

Peahippo is right. In Fort Wayne, Indiana, one must first go downtown and make a transfer. The buses come only once an hour, and they don't run at all on nights, Saturday evenings, Sundays, or holidays. Biking on streets designated 40 mph (65 km/h) or higher is dangerous because Fort Wayne has no designated low-speed vehicle lanes.


lj65
[ Parent ]
How do you Tokyo Drift 4 Max. Efficiency????? (2.00 / 6) (#76)
by Egil Skallagrimson on Fri Jun 08, 2007 at 11:55:14 AM EST


----------------

Enterobacteria phage T2 is a virulent bacteriophage of the T4-like viruses genus, in the family Myoviridae. It infects E. coli and is the best known of the T-even phages. Its virion contains linear double-stranded DNA, terminally redundant and circularly permuted.

Well... (none / 0) (#103)
by BJH on Sun Jun 10, 2007 at 06:45:17 AM EST

...first, you find a young Japanese hottie, put her in your car, drive back to your place, spend the next three weeks in bed and forget about going anywhere else.
--
Roses are red, violets are blue.
I'm schizophrenic, and so am I.
-- Oscar Levant

[ Parent ]
i hate cars (1.75 / 4) (#77)
by raduga on Fri Jun 08, 2007 at 12:39:03 PM EST

if people read the article and follow your advice, there may be a few less cars (and a few less tards) left on the road-ways, so +1.

Another Tip (2.33 / 3) (#81)
by frankwork on Fri Jun 08, 2007 at 05:32:28 PM EST

One of those obvious-but-subtle ones: the earlier you brake, the less momentum you need to burn off to avoid a temporary obstacle (e.g. car in your lane waiting at a traffic light).

Do it right (2.33 / 6) (#83)
by asolipsist on Fri Jun 08, 2007 at 08:02:12 PM EST

Your advice is for sissies, if you're going to strive for maximum efficiency do it right:

Braking: don't do it, never stop for stop signs, traffic lights, or small pedestrians.

Corners: Never break, conservation of momentum is paramount. Always hit the apex, regardless of what lane it is in.

Starting: only do this once at the beginning of a journey and do it slowly.

Drafting: the closer you can get the better, always draft within at least 10ft of the vehicle in front of you, and the larger the vehicle the better.

Weight: the lighter your car the more fuel efficient it will be, remove your exhaust system, airbags, ac system, catalytic converter, back seats, spare tire, seat belts, hood, trunk, and only put enough gas in the tank to get where you're going.

Tires: get the smallest and skinnest tire you can find, over inflate them as much as possible.

Engine efficiency: we've gone over this a bit already, but remove any energy sapping systems: most of your exhaust (especially the muffler), the air filter, the cat converter, and everything connected to your alternator besides the starter and pumps.

you're either with us, or you're with al-Qaeda (3.00 / 3) (#89)
by the spins on Fri Jun 08, 2007 at 09:17:11 PM EST


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[ Parent ]

Slow down? (1.00 / 2) (#87)
by the77x42 on Fri Jun 08, 2007 at 09:03:27 PM EST

In my 1990 Honda Accord I do mostly double the speed limit in most cases. 80-90 km/hr in a 50 zone and about 120km/hr on the 90 zone highways. The idea is to get my manual transmission into fifth gear as much as possible. I'm frequently getting over 600km per tank, which is around 35mpg.

You also have to learn to run all yellow lights because idling = more gas used.


"We're not here to educate. We're here to point and laugh." - creature
"You have some pretty stupid ideas." - indubitable ‮

lol (none / 1) (#130)
by tetsuwan on Mon Jun 11, 2007 at 01:14:30 PM EST

The American version of the 1990 Honda Accord has a 65l tank, which would translate to 22 mpg. With a 50l tank your mileage would be less than 29 mpg.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

yup, you're right (none / 1) (#133)
by the77x42 on Mon Jun 11, 2007 at 06:21:04 PM EST

stupid me. i get somewhere between 20-25mpg. a friend with the exact same car, but automatic, is only getting between 15-20mpg.


"We're not here to educate. We're here to point and laugh." - creature
"You have some pretty stupid ideas." - indubitable ‮

[ Parent ]
One thing that sums these up: (2.40 / 5) (#98)
by garote on Sat Jun 09, 2007 at 08:24:20 PM EST

My father and my driving instructor both game me the same advice, each without knowing the other:  The one thing you need to concentrate on is driving SMOOTHLY.  Smooth movement around turns = minimal braking.  Smooth movement around traffic = gentle acceleration.  Smooth acceleration off a stop light.  Smooth braking = braking light = braking as little as possible.  Pretend you're on a river, swinging gracefully around obstacles.  Concentrating on that one thing will bring you into conformance with almost every rule on that list.

I'll second that (none / 0) (#102)
by Pholostan on Sun Jun 10, 2007 at 04:29:04 AM EST

At least five people independent of each other have told me almost exactly the same thing. All are senior drivers with thousands and thousands of miles behind the wheel. This stuff works.
- And blood tears I cry Endless grief remained inside
[ Parent ]
Brakes (none / 0) (#174)
by Eccles on Sat Jul 21, 2007 at 12:46:56 AM EST

Minimizing your brake use also helps them last longer, so you save money as well as gas. (I just paid for a $365 brake job, so I know of what I speak.)

[ Parent ]
Notes on drafting a truck (1.50 / 2) (#107)
by pyro9 on Sun Jun 10, 2007 at 03:17:55 PM EST

Develop a feel for your car, especially for road/air resistance vs. accelerator.

As you approach the back of a truck you can feel the car "settle in" to the lower density air pocket in front of the turbulant wake of the truck (which is well behind the truck itself). It feels almost as if the wake is pushing the car forward (though it's actually the air NOT pushing the car back so much).

That point is the sweet spot for maximum safety and mileage. I would need a wind tunnel to prove it, but IMHO, the extra boost from the wake coming together "squeezzing" the car forward is significant. Moving closer will actually lose some of the aerodynamic advantage.

I have tested that by moving a bit closer then letting off of the gas until the car just starts to fall back. When it reaches the sweet spot it gets just enough boost to match speeds with the truck w/ no throttle adjustment.


The future isn't what it used to be
it's a lower pressure air pocket (2.50 / 1) (#122)
by the spins on Mon Jun 11, 2007 at 11:03:30 AM EST


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[ Parent ]

So the temperature is lower in the pocket? (none / 1) (#124)
by tetsuwan on Mon Jun 11, 2007 at 12:08:57 PM EST

Otherwise the density is lower.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

negligibly so (none / 0) (#126)
by the spins on Mon Jun 11, 2007 at 12:21:18 PM EST

why density is even considered is beyond me; pressure is the relevant property to consider and it changes a lot more than density at subsonic velocities. to answer your question: yes.

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[ Parent ]

if you say so (none / 1) (#128)
by tetsuwan on Mon Jun 11, 2007 at 12:54:56 PM EST

I think what you want to say is that even a small pressure difference can make a big difference, because p is proportional to rho*T, and the density and temperature are the only quantities that can change in this case.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

no, that's not what i said. (none / 0) (#129)
by the spins on Mon Jun 11, 2007 at 01:03:16 PM EST

i said density change is negligible. pressure change is not. in accordance with the ideal gas law, the temperature does change in the low pressure pocket, but it changes back to ambient as the air leaves the pocket.

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[ Parent ]

Good (none / 1) (#131)
by tetsuwan on Mon Jun 11, 2007 at 01:16:43 PM EST

then we agree that there is in fact a substantial temperature change in the low pressure pocket. Maybe one could put a six pack there to cool it down?

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

Volume not constant (none / 0) (#150)
by Xenophon Fenderson, the Carbon(d)ated on Wed Jun 13, 2007 at 07:57:07 AM EST

The volume of that low pressure air pocket does not stay constant, seeing as it is unconstrained (being the open atmosphere behind a truck and all).  The temperature behind the truck is roughly constant (in my experience), the pressure is low (according to this discussion), so the volume of air will increase.  Yes, this affects the density of the air, but I'm not aerodynamics-ninja enough to tell you by how much, or whether the effect is significant at speeds less than Mach 1.  The other fellow seems to think that the density difference is negligible at the speeds of your typical car or truck.

--
Rev. Dr. Xenophon Fenderson, the Carbon(d)ated, KSC, mhm21x16, and the Patron Saint of All Things Plastic fnord
I'm proud of my Northern Tibetian heritage!
[ Parent ]
That's my problem (none / 0) (#151)
by tetsuwan on Wed Jun 13, 2007 at 10:12:54 AM EST

Although the low-pressure pocket is hardly an isolated system, I do think it would be odd for the temperature to decrease significantly, that is on par with the pressure. Thus the air density would go down.

Njal's Saga: Just like Romeo & Juliet without the romance
[ Parent ]

Drag Equation (none / 0) (#135)
by pyro9 on Mon Jun 11, 2007 at 07:07:48 PM EST

Because drag is directly proportional to the density of the medium. Pressure is only secondary (in the sense that lowering the pressure at a constant temperature will reduce the density).

That is, reduce the density to half of STP by increasing the temperature at a constant pressure and the drag will be reduced. OTOH, half the pressure by cooling to maintain a constant density and drag will be unchanged compared to STP.

Have a look at the drag equation


The future isn't what it used to be
[ Parent ]
yes, i'm quite familiar with that equation (none / 0) (#136)
by the spins on Mon Jun 11, 2007 at 08:53:34 PM EST

one obtains the vector sum of the forces acting on a body by integrating the forces normal to the surface over the entire surface. these forces are obtained from static pressure at the surface. that is why pressure is important, especially when we are considering a situation in which the pressure drag would be the drag component affected. for the equation you cite, this is embodied in the drag coefficient (along with other things such as skin friction due to viscous effects).

as i have mentioned elsewhere, at freestream velocities appreciably below Mach 1 (the upper limit is generally accepted to be around 100 m/s at sea level), compressibility effects can be disregarded and thus density can be assumed constant.

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[ Parent ]

running stop signs and red lights whenever possibl (1.50 / 4) (#132)
by balsamic vinigga on Mon Jun 11, 2007 at 02:38:48 PM EST

is also a great way to conserve fuel!

---
Please help fund a Filipino Horror Movie. It's been in limbo since 2007 due to lack of funding. Please donate today!
I already do half of these.... (1.50 / 2) (#139)
by DavidTC on Tue Jun 12, 2007 at 01:31:39 PM EST

...not because I care that much about mpg, but my very first car was a huge honking tank, a 78 Chevrolet Malibu. A huge honking tank with radiator trouble. I'd have to fill up the radiator before I went anywhere.

If I drove carefully, accelerating slowly, coasting to stops, avoiding traffic...I could make it the ten miles to school just fine. And back. In moderately heavy traffic.

My brother once drove that thing back from school (And in much less traffic!) and it overheated twice. (That car, of course, was built when car engines didn't get damaged by overheating.)

I still drive like I'm scared of the brake pedal, as a passenger put it once. I see a red light half a mile ahead, I'm coasting the entire distance. Either I'll need to stop when I get there, and it doesn't matter, or the light will change and I'll actually get through it faster being 100 feet away going twenty than 0 feet away going 0. I might be going 45 at the top of a hill on a 55 mph road, but I'll be going 65 at the bottom.

And I drive way behind other cars if there's no chance of someone someone merging in front of me. (And sometimes even then.) They can speed up and slow all they want...if I'm not planning on passing them, I fail to see why I should be so close as to have to do whatever they do.

It drives passengers crazy, but they have to admit I don't get anywhere any slower than normal drivers do. The only place I drive 'slower' is places where I couldn't physically get there faster anyway. Getting to a red light faster isn't going to help(1), getting behind someone at a stop sign faster isn't going to help as long as you're there when they leave, etc.

Something like half the 'speed up and slow down' I see people doing is just nonsense that doesn't accomplish anything. People have some crazy mental concept that being physically closer at a specific point in time is going to get them somewhere faster, but that's rather like starting your Hawaiian vacation from the west side of your property, or getting to the airport 24 hour early. You will get to Hawaii at the exact moment your flight, which you are not in control of, lands there. Not before and not after.

And I actually get the estimated gas mileage for my car, which I hear is unusual.

1) Okay, it actually can help with some triggered lights, and there's one place where the light is always green the way I'm not normally driving until someone drives up from my direction, so my car always triggers it. So I've started actually driving up to that light like normal, because I feel silly when I'm coasting up to it and I realize my time there isn't going to count until I cross the trip wire.

-David T. C.
Yes, my email address is real.

simple mechanical changes for fuel economy (1.50 / 1) (#153)
by krkrbt on Wed Jun 13, 2007 at 05:54:02 PM EST

The best fuel economy I ever got in my Ford Escort was 38mpg, when I ran it as near to a constant 65 mph as I could. This was significantly better than my usual 30-32mpg. Posted about this experience in a diary: I ran out of gas once..." (it was about eight hours before it sputtered & died).

Anyways, some mechanical things you can do to improve fuel economy:

  • Get a washable K&N Air Filter.  My mom's husband said it gave him 1-1.5mpg on his Chevy Avalanche (the suburban/truck beast), which was pretty huge when you're only getting 15-18mpg. I just dropped one in my Escort replacement, and don't know yet if it's any good for the small car.

  • Synthetic oil throughout the drive train.  Engine, transmission, etc. This is supposed to be good for 10%...

    The manual transmission on my Toyota MR2 was griding on 1st and 2nd. I was resigned to a rebuild, but replaced the standard Automatic Transmission Fluid with Redline's synthetic Manual Transmission Lubricant. The grinding stopped, don't remember if it helped the fuel economy or not. Probably not significantly - the head gasket needed fixing at the same time, and the fuel economy for that car sucked until the next owner (my father) finally got that fixed.

    If your engine has a significant number of years/miles, I strongly caution against switching the engine oil to a full synthtetic, as it's likely to clean all the gunk out of your engine, and it'll start leaking/burning oil, or worse. I switched my MR2 to synthetic oil soon after I got it (the odometer said 55k miles, but the car actually had something like 105k), and it promptly put a rod through the side of the engine block. Coincidince?  I don't know.

    Synthetics can save your engine, though. My mom's then-bf switched her Subaru to Mobile-1 Synthtetic. One night she was driving home (60 miles uphill) and noticed that the 'check engine' light was on. Took the car to the bf's shop the next day, and they determined that a rat had chewed through the radiator line, emptying all the coolant from the system. They replaced the hose & coolant, and Mom & her now-husband are still driving that car some 5+ years later.


  • Work on your aerodynamics.  Some of the guys at Gassavers.org have some good suggestions - underside of the car, blocking up the holes (radiator vents) on the front, etc.
  • I haven't gotten to this on my 'new' car yet...

My best fuel economy runs on both my Escort and MR2 came from sustained runs at 65mph. My Escort recently went down for the count (no compression on cylinder 4, loose intake valve seat?), and my replacement car is a 1994 Honda Civic VX. I've put about 6,000 miles on it in the last month and a half (4,000 mile road trip), and the mileages have been all over the place. Best was 57mpg between eastern Arizona and northern New Mexico (right after upping the tire pressure by 5psi); worst was 36mpg when I let my girlfriend drive at 80mph for ~240 miles. My average is 45.89, which includes 1,000 miles at <40mpg due to a bad  Lean Air Fuel sensor (basically, a fancy 5-wire oxygen sensor that lets the engine sip gas instead of guzzle it, as appropriate). Not bad for a 13 year old car with 135k miles.

I do wonder why hybrids' fuel economy sucks so bad (including that of the "sacred" Prius). I think it's conspiracy, but that's another post... :)

Improve your mileage - REAL tip (2.00 / 3) (#156)
by luggage on Thu Jun 14, 2007 at 07:07:44 PM EST

First - as some of more versed engineers here will explain better (since it has to do with the flow of particles through finite-in-size container), leaving slowly a traffic light and clearing the intersection slowly will have the effect of clearing 3 cars through 15 seconds light instead of 10. Remaining 7 will happily quaff fuel for another 1 minute and 15 seconds until next green comes at which point there will be 15, not 10 cars in line and only 3 will leave the intesection leaving 12 behind ... you get the point.


All of this without mentioning how much assholeness one displays by believeing to be Lord Of Everybody Else's Time. Just because you don't have to be anywhere in any particular time does not entitle you to slow everybody else down - even if they don't have to be anywhere in any particular time, either.


I accelerate as hard as I can, use stick to control deceleration by downshifting ( and, as a consequence, revving the engine) and hit breaks at the last moment. Right now I also use AC since it's 90 degrees F outside. With all that, I still get better mileage than you - 35 mpg minimum. In a car - not motorcycle. A car that could haul small U-Haul trailer up Rockies from CO to CA.


There's your real tip to improve your mileage without being an asshole - in three letters, it's called TDI.


Now if you REALLY want to push revolutions here, consider your 1st amandament right to "petition the Government for redress of grievances" and ask them to explain to you how it is possible that:
a) Ford sells a car in UK (and rest of Europe) that will get 55-60 mpg on a freeway and sells identical model in US but best mileage you can get in US model is 32-35 mpg
b) Chrysler sells its all new 2007 Sebring in Europe that gets 38 mpg on average but it will not sell it to US residents - best THEY get is 22-25 mpg
c) GM sells (what will be called Saturn Astra in couple of months) Astra in Europe under Opel nameplate and that thingy gets comparable mileage to Ford's vehicle - 55-60 mpg on a freeway


Consider your rights spelled out in 2nd amandament, too, while you are at it.

I didn't recommend slow acceleration (1.50 / 2) (#164)
by Liar on Sun Jun 17, 2007 at 07:00:08 PM EST

I recommended moderate acceleration which--in case you don't understand the word in this context--is somewhere between fast acceleration and slow acceleration. In fact, since I recommended accelerating at the peak of the torque curve, that means that your pedal is depressed about 75% of the way down (depending on your vehicle).


I admit I'm a Liar. That's why you can trust me.
[ Parent ]
Here Are Numbers (3.00 / 2) (#169)
by vnutz on Mon Jun 25, 2007 at 03:03:12 PM EST

I couldn't help but notice that many people commented "where are the numbers".  Almost a year ago, I posted an article on OmniNerd that used data sampled directly from the engine computer while driving to prove the differences in fuel economy based on different driving techniques.  Please read Improve MPG: The Factors Affecting Fuel Efficiency for more details.

My favorite bit of information from that study was taking the amount of fuel consumed at 55mph versus 75mph and seeing who burned more fuel driving 1000 miles.  Most people immediately say that driving 75mph and arriving five hours earlier saves gas by running the engine for less time.  You actually use almost 25% less gas driving longer at 55mph than speeding at 75mph.  All simple math derived from the article.

So - if you want cold hard numbers, read the article.

Numbers (none / 1) (#170)
by luggage on Tue Jun 26, 2007 at 10:01:11 PM EST


I never said that driving fast saves gas - I merely tried to make parsimonious SUV-driving people aware that their behaviour affects other drivers and that they are not alone on the road. Hence, buy TDI. Or, more simply, buy a car - not a bus.


Speaking of numbers, why our Big Three from Detroit want to avoid at any cost selling to US residents cars that get sometimes 50% better mileage when sold to Europeans? And we are talking same models here, no need for new presses for sheet metal, no new lines of welding robots etc ...

[ Parent ]
Driving for Maximum Fuel Efficiency | 176 comments (152 topical, 24 editorial, 10 hidden)
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