55 is lame

has anyone really done any tests to figure out with modern cars what is the most feul efficient speed

somehow i think that there shouldn't be any difference at 55 then at 65

modern engines can go fast at low rpms

Did anybody mention the extra revenue it brings in from speeding tickets?

"has anyone really done any tests to figure out with modern cars what is the most feul efficient speed" - Klifferd

Oak Ridge National Laboratory (2003)

55 is lame

has anyone really done any tests to figure out with modern cars what is the most feul efficient speed

Yes 2007 Toyota Camry 55 mph 40mpg, 65 mph 35 mpg, 75 mph 30 mpg.

Klifferd it is not the rpm's but rather the wind resistance on the vehicle. Go from 55 to 65 and I do believe wind resistance effectively doubles.

In addition, for every penny of savings on the fuel front, we would lose dollars as hourly workers who handle transportation would instantly be something like 20% less productive

When a great economic thinker such as this throws around technical the terms "would instantly be something like" you have to marvel at the knowledge they must have.

What if the loss in productivity was instantly something like only 5% less? 1%?

How many 12 hour weekend trips does the average family take? How many three hour trips to the beach? How much does going to the beach contribute to the economy?

So today Gov. Arnold's sagelike advice to Californians:

1) Drive less

2) Drive slower

3) Keep your car tuned up

Thanks for that, Arnold

This post is from a poster over at "American Thinker", who appears to one of the few with a brain in their head:

I drive the speed limit. I dispute the assertion that much/most highway traffic is commerce. If this were so then those not engaged in commerce would drive slower because it would save them money. They don't. I never, and I do mean never, pass anyone. Every single vehicle, be it a huge Winnebago, a tiny Civic, an empty pickup, a huge SUV with one person aboard...all of them pass me. People speed because they want to be wherever they are going in the least amount of time, regardless of cost. In other words, they are driving mindlessly, more intent on getting ahead as fast as possible by lining up in the fast line bumper to bumper at 70mph than thinking about productivity and efficiency.

Studies continue to show the most efficient speed is 55 - 60 and common sense tells us that accidents have a lesser effect on vehicle damage and personal injury at lower speeds. Nevertheless, people go as fast as they think they can without getting a ticket, even buying radar detectors to allow it. It's just the old American independence - that has brought us to this brick wall of oil price increases we now face. It isn't the gov't's fault. It isn't the car manufacturers' fault, it is OUR fault for not thinking about what we do and pretending there are no limits, speed or otherwise.

Improving efficiency of commerce, taking advantage of aerodynamics, etc., etc. are all rationalizations. Even the truck lines are installing governors to keep their drivers from exceeding certain speeds. Can we argue with those whose money is on the line and address it thinking clearly of the bottom line that they are thereby lowering the productivity of a business to which speed is critical?

The bottom line here? People do not want to drive slower and by not doing so up to now have set the stage for being required to do so in the future. We have not been thinking ahead, or at least not beyond our immediate destination when we get behind the wheel.

Posted by: CB | July 14, 2008 05:01 PM

Oh, wait...here's another!

Wow...there are a couple of actual "thinkers" posting over at "American Stinker"...who'da thunk it:

I agree that Congress should not be playing around with speed limits as a conservation ploy. Speed limits should be set for safety considerations.

I would much prefer to see realistic speed limits that are actually enforced as posted. Cut the hypocrisy.

I know from a life-time of pushing airplanes that there are signifcant costs to going faster than the optimum speed. Airlines know that these costs are not offset by productivity gains. They make a constant effort to educate and discipline aircres to this fact.

My American sedan is most efficient at 60 mph. I pay a penalty for speeds faster or slower than that. In the interest of my pocket book that is the speed I try to drive now. I know that the time lost will be negligble.

There is typical ignorance of actual time-distance factors being expressed here.

Ten mph makes a significant difference on a long-haul trip. It does not make an appreciable difference to a delivery person or the casual driver.

Just do some simple arithmetic. A 100 mile trip at an average speed of 60 mph take 100 minutes. The same 100 miles at 70 takes 86 minutes. A difference of 14 minutes. So how about that delivery guy? If he is running 15 miles between stops he is saving a whopping 2.2 minutes on each leg. For the casual driver or short-haul business there are much better ways to improve or preserve productivity.

Long haul drivers need to actually do some analysis based on real data to determine what speed to drive. They might be surprised.

Posted by: BobG | July 14, 2008 05:39 PM

Yes 2007 Toyota Camry 55 mph 40mpg, 65 mph 35 mpg, 75 mph 30 mpg.

I don't care. I live in the westerns U.S., where 55 miles per hour is so dreadfully fucking slow, when driving on the interstate, that it's dangerous. Boredom kills! I wont do much more then the speed limit, but leave the speed limit alone. Boredom kills! Find some other way to save fuel.

wont should be won't....damned old fingers

I don't care.

Posted by Whatsleft

That is the problem.

Hey why not let 10lbs of air pressure out of your tires at the same time.

"That is the problem."

The problem is that in order to function properly, our society requires an increasingly scarce resource that is mostly controlled by foreign entities. Actually, I'm not so sure the foreign entity part is that much of a problem. Its not like American corporations wouldn't gouge us as much as possible if they controlled oil production completely.

Sully,

That's right. And instead of driving 10 mph slower on the daily commute the American consumer just "don't care".

I won't exceed 60 on the interstate and won't go more than 55 in the urban areas. Why? Because I am all for giving the terrorist oil producers less money every single week.

But everyone else seems to think that their 25 mile commute will be agonizing too much to bear if they did less than 70.

Again it all comes down to personal sacrifice to make America stronger. Far too long the public has had the opinion (promulgated by the corporate media) that we can have whatever we want when we want it and without any consequences.

When gas hits $8 per gallon the bithcing and crying will be defeaning, but hey don't ask them to sacrifice a little.

Just think how much less oil would be used if people slowed down and got 20% better fuel economy. But I guess that is too hard to do for this pussified population. God help us if there is ever a real war.

Dave,

you're that guy that has a line of cars behind him for 6 miles, riding along, singing to the radio, while some guy back there has so much road rage he could bust a blood vessel.

Rock on Dave.

"I won't exceed 60 on the interstate and won't go more than 55 in the urban areas. Why? Because I am all for giving the terrorist oil producers less money every single week."

OK, good for you. Just stay out of the left lane.

"Because I am all for giving the terrorist oil producers less money every single week."

So if you give them $50 a week for 4 weeks or $40 for 5 weeks, you see a huge difference?

"When gas hits $8 per gallon the bithcing and crying will be defeaning"

And then maybe we'll do something to really address the problem, which wouldn't be to use less gas. It would be to use something other than gas.

2005 Nissan Altima
At 75 mph average...420 miles on a 17 gal fillup.
At 55-60 mph average...500 miles on a 17 gal fillup.
Do the math kiddies and if you're not willing to slow down, shut up about gas prices.
The reality is, on most commuting or short trips, you get there about 5 minutes faster by speeding.

Sully,
That's nice but gas will be at $8/gallon YEARS before a solution is found. When a solution is finally found, it should be hovering around $12-15/gallon.

The reality is, on most commuting or short trips, you get there about 5 minutes faster by speeding.

Posted by evilpolock

Good to point that out, evilp.

Each vehicle is different, 55 is a speed that has been thrown around since the 70's but it includes pickup trucks, vans and suvs. Many cars are more efficient at 70 then 55 now, partially due to the gear set that are common. A while back a three speed auto or a four speed manual with a one to one 4th were common now overdrive is a given. As you lower the speed at which your engine is spinning you drop yourself out of your power band thus running inefficiently. Many cars can get higher mpg's when running at a higher rate of speed pushing them into the bottom of their power band instead of out of it completely. You can see this by installing a vacuum gauge to your intake manifold and watching your pull, the more inches of vacuum you pull the closer you are to running efficiently.
I offer my car as an example. My daily driver is a Lincoln mark viii, it is rated at 26 mpgs i however routinely get 28 and i drive fairly hard. Recently i found that i can get just about thirty if i cruise around 70 to 75 but that drops to about 27 at sixty. At 60 i run about 1350-1400 rpms but 75 gets to 1750 or so those extra few hundred rpms make a big difference. Past 80 i start loosing mileage again which seem to set my optimum speed at 70. Then you have my truck, The thing make 10 hwy on a great day at 60 but gets almost 13 at 45 mph due to is somewhat less then aerodynamic profile(more like a wall.) Add those together and 55 seem like a happy middle ground but in reality neither vehicle is running at peak efficiency and no one wins. Now does that make sense? Setting a certain speed for efficiency reason is like setting a caloric intake for everyone across the board from a 250 pound wrester who needs 7000 to a 78 pound wuss needing 1200 would you make the eat the same?

And then maybe we'll do something to really address the problem, which wouldn't be to use less gas. It would be to use something other than gas.

Amen to that.

As for the $50 x 4 week vs $40 x 5 weeks, your math is flawed.

There is a difference when paying $50 x 5 weeks and $40 x 5 weeks. If you are going to do a cost comparison, you need to look at the costs over the same period of time or units.

Or do you enjoy paying $10 extra per week?

Many cars are more efficient at 70 then 55 now, partially due to the gear set that are common

Posted by salamandagator at

Which ones?

Again, it has more to do with wind resistance than gearing.

According to the U.S. Department of Energy (DOE), as a rule of thumb, you can assume that each 5 mph you drive over 60 mph is like paying an additional $0.21 per gallon for gas (at $3.00 per gallon).

Power

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power

We are talking two different things here.
First, you are talking drag. The drag coefficient of a car determines the force necessary to propel it through a set density. The cars today are designed to have much lower coefficients then those of past creating a more economical vehicle, but that is only part of the equation. Another large factor is the efficiency of the engine, my point. Both play major roles but you cannot factor out either. If your engine is "lugging" you are not using it's power in an efficient way. Take a diesel for instance, for this purpose i'll say a 96 ford powerstroke f250. They have a very narrow power band and if you stay in this band you run in an efficient manner. I have found that 55 is an ideal speed for that truck, 65 and the mpgs drop to 16 or so 75 and your at 10. This is not due to the resistance but instead has everything to do with the powerplant. If it were all about drag than i would hardly matter what engine size you were running because the power needed would be the same, this is obviously not the case. When an engine is lugging you are not using your fuel to its potential, much ends up burnt in you cats. The better you can convert the fuel into kinetic energy the less you will use. It is the reason you dont drive a 5 speed in 5th at 25 it is the reason we dont cruise on the highway at 500 rpm.
Now there are modern advancement that help with this such as variable cam timing and lift which help control the power band, but especially with the low displacement engines you just can't go down that far. I would seem almost backward but if they lowered the limit to 55 i would probably need to put in 3.73s or at least 3.55s to archive my current economy.
As to your "rule of thumb" that still includes trucks and suvs which are much more susceptible to wind resistance but that skews the conclusion. SO the drag can be offset by the efficiency of the engine and as you approach the more aerodynamic cars this is more frequently the case.

Interesting stuff, SAL. Thanks for the info.

Sal,

You did not answer my question which cars are more effecient at 75 than 55.

I doubt they exist, but would like to know. I just may buy a couple.

Sal, you are trying to sell me that the wind resistance at 75 is not the reason fuel economy drops, but rather the gearing? C'mon lets be honest. How many cars start their top gear at 75 mph? Most four speed automatics start the top gear at 40mph, that is close to where the car will be the most fuel efficient as the wind resistance is the lowest and the engine is burning the least fuel.

After that you are just pushing more fuel into the engine to overcome the increasing wind resistance against the front of the car. Some models may have more gears so that top gear starts at a higher speed, but most do not.

The wind resistant doubles for every ten mile per hour the speed increases.

But I still want to know which cars are more fuel efficient at 75 than 55. I think you are blowing smoke.

Hey why not let 10lbs of air pressure out of your tires at the same time.

Posted by 726

If you think driving 55 is keeping money away from the Arabs, or driving 55 is going to make a gallon of gas any cheaper, you're nuts. If we're not using the Arab gas someone else will. If we pump more gas in the U.S., its still going too go to whoever is willing to pay the most for it.

The only time I drive that fast is when I'm traveling long distance. Otherwise, I don't even live within 60 miles of an interstate highway. When I go on one of those trips, I'm going to drive at least 75 mph. I don't care if it costs me an extra $15.00 to save an hour of drive time. What's your time worth? Maybe youre retired, I dont know, but if your time is worth so little that you'd rather drive slow to save gas on a long trip then feel free. Just stay in the right lane, and leave the damned speed limits alone. Forcing others to save gas by changing the speed limits is not a solution.

If you think driving 55 is keeping money away from the Arabs, or driving 55 is going to make a gallon of gas any cheaper, you're nuts.

Yeah how fucking silly of me to actually assume that by INCREASING my fuel economy would decrease the amount of money I personally send to the terrorist oil exporters.

Keep on saying over and over, conservation is not part of the solution..... conservation is not part of the solution.

I don't care if it costs me an extra $15.00

That is exactly the mindset that won WWII.

God help us if we have to fight a real war with this bunch of gimme gimme gimme I want it all now assholes.

"How many cars start their top gear at 75 mph"

probably the 6 speed manual transmissions

i had a celica
and 6th gear did not have enough power until about 70 mph

just trying to understand

if wind resistance makes driving at 55 better then 70

then does that mean driving 30 is even more fuel efficient?

"You did not answer my question which cars are more effecient at 75 than 55."

I gave an example in my first post. My car does, it is a dohc 4.6 V8 Lincoln mark viii first year 1993. It has a 4-speed electronically controlled automatic with a .70 overdrive in the back i have 3.07's. I have a buddy with an 07 impala and another with an 06 cobalt say the same thing. I have a 79 zephyr that i put a 302 in and got 18 in overdrive at 60 but 20 in third due to a .62 overdrive and 2.73 gears. Not to mention my wifes 4 banger mini truck that can barley hold 60 with the AC on but 70 is no problem, oh yea it gets 30 with a tonneau on I have also a 93 firebird 3.4 5-speed, gets 33 at 70 somewhat less at 60. Now my firebird and Lincoln are fairly aerodynamic in at .34 and .33 DC respectively but that is only part of their efficacy.

Once again i pint to the difference in mileage between engines. If it was all about drag then a larger engine would make the same economy. There is always a few mpg drop between a 6 and an 8 or a four and a six, do V8's induce more drag? No, i thought not. If engine efficiency had no effect then why are we playing with variable displacement or vvt? If you fail to take into account all factors your conclusion is invalid. So work up a hypothesis, be sure in include drag, engine efficiency, tire size, transmission, final drive, weight, altitude, fuel, state of charge, accessory health, tread compound, tire pressure, amongst others then get back to me and tell me it's all about drag.

Yeah how fucking silly of me to actually assume that by INCREASING my fuel economy

I said "but if your time is worth so little that you'd rather drive slow to save gas on a long trip then feel free." Did you not comprehend some part of that?

would decrease the amount of money I personally send to the terrorist oil exporters.

If it makes YOU feel good then by all means, DO IT. That still gives you no cause to force others to comply. Since terror seems to be your predominant reason, instead of imposing slower speed limits, why don't you lobby the government to impose boycotts of Arab oil, to keep the money out of the hands of terrorists? (I already know your answer, but I'll wait anyway.)

Keep on saying over and over, conservation is not part of the solution..... conservation is not part of the solution.

I might worry about it if there were more compelling proof that a shortage exists. I haven't had any trouble buying gas lately, have you?

then does that mean driving 30 is even more fuel efficient?

WTF! If you've got nothing but time why not do 10! Please, just do it on the shoulder.

I gave an example in my first post.

I don't want an example or what "your buddy" says. I want a list of cars.

Otherwise you are just blowing smoke.

I can say my car gets 100mpg at 95. Don't make it true.

I have also a 93 firebird 3.4 5-speed, gets 33 at 70 somewhat less at 60

Now there is some facts you can beleive!

haven't had any trouble buying gas lately, have you?

Posted by Whatsleft

No but there are plenty of Americans that are having trouble buying gas and food. Try not to sound elitest.

Oh, and just so you know the 55mph is based of a 1997 study
Posted by salamandagator

Really? I wonder why it would be published in the June 2008 Consumer Reports then. Just another mystery in life. Like cars that get better mileage at 75 than 55.

Ahh, so what you are saying by your links is agreeing with me. If you combine the suv and the car the "optimum" mileage at speed is lower. This would require that many cars would in fact be well above 55 to make the average the the department of energy sets out. I am slightly more inclined to believe those numbers then your, ahem "studies." Mind you that the study was conducted in 97 and vehicles are even better now but it would still lend itself to proof of my point. If you want to argue that to make a 55mph average based on cars that all peak below that is possible go right ahead we could all use a good laugh. B

No but there are plenty of Americans that are having trouble buying gas and food. Try not to sound elitest.

I'm not trying to sound elitist. I'm saying if there is no shortage, then lowering the speed limit is not going to lower prices. The only way to significantly lower prices is to find something to compete with oil.

But then your reasons weren't about prices, they were about sending money to 'terrorists'.

Ahh, so what you are saying by your links is agreeing with me.

Maybe you should read them again.

65 MPH = 20.4 MPG
70 MPH = 18.9 MPG
75 MPH = 17.3 MPG

26 PERCENT DROP

In the 2005 Explorer, there was a 26 percent drop in fuel economy from 55 mph to 75 mph.

Tell me again just how that agrees with your assertion.

I am still waiting for that list of cars. Got a link? I didn't think so.

The only way to significantly lower prices is to find something to compete with oil.

But then your reasons weren't about prices, they were about sending money to 'terrorists'.

I agree. We will never drill nor conserve our way out of it.

We need to develop alternate fuels.

Yes I said terrorists. Every time we buy 1 barrell of oil from Saudi Arabia we are supporting terrorists.

SO, 55 IS THE BEST SPEED? NOPE

So, the moral of the story is drive 55 to get the best fuel economy, right? Well, not really. The 2005 Ford Explorer peaked at about 28 miles per gallon at 45 miles per hour -- 10 more miles than a speed of 75 mph.

So how do you think they did a test on a 2005 Ford in 1997?

And if you read my post you would see that I stated the top gear on most cars start around 40 mph at which point you are using the least amount of fuel for the miles you are traveling.

So, of course the fuel economy of 28 miles per gallon at 45 mph is much less efficient than the 17.3 mpg at 75 mph. At least in your world.

Is up down too?

"Tell me again just how that agrees with your assertion."

Hmm, maybe because i have repeatedly tried to help you understand that trucks and suv skew the averages. Maybe because it is so prominent in larger vehicle and the average is still 55 it must mean that many are better above. Maybe because singling out one vehicle especially one not known for economy and applying the result across the board is at best a logical fallacy.

Fine, then post a link to the list of CARS that have better fuel economy at 75 than 55.

Every time we buy 1 barrell of oil from Saudi Arabia we are supporting terrorists.

We can't conserve our way out of that either, unless Exxon and their cohorts are willing to stop buying oil from certain exporters. What are the chances of that?

It's a frustrating situation, made worse because there's little we can do about it.

There is little that any of us can do, but my point it I will do whatever I can to even cut it a little.

10% increase in fuel efficiency may mean nothing to any one person, yet if everyone saved 10% what do you think that would do to prices?

An easy way to save 10% is to drive slower. 50 mph is the sweet spot on most cars and trucks on the road today, anything after that is using more fuel per mile.

Of course there are some that would blow smoke up our asses that cars are more efficient at 75, but they have no third party info to support that claim.

If you don't want to drive 55 or 60 and feel the need to go 75, fine, but don't disengenuously say that going 75 is more fuel efficient. The science does not support it.

Now some high end sports cars may in fact be more efficient at higher speeds. I think the Corvette has a six speed tranny which theoretically should give it better fuel economy once the top gear kicks in, but the vast majority of cars on the American roads today have a four speed auto or five speed manual tranny which would get the best fuel economy at the point where that top gear is engaged.

"So how do you think they did a test on a 2005 Ford in 1997? "

Wow, you are an idiot. I post a government issued study that was done in 97 which is the most current i have found from the dept of energy and you counter with a story that is no more scientific than my personal experiences then claim it as accurate as the DOE's. You have no grasp on reason nor averages if you don't see that having vehicles under 55 would require those over 55 to average 55.

I cannot link to a study as they are all pay per use. However, i have provided the results of the DOE study which averages all vehicles and hit 55 on average it does not take a genius to figure that one out. I have also pointed out my own examples which are probably as scientific as your links, now you may call me a liar thats fine but you do this with out proof or evidence to the contrary. You have fallen to your last resort, repeat, repeat, repeat and attack me on another thread, it is time to give it up.

"The science does not support it."
You obviously don't even know what that means.

"Now some high end sports cars may in fact be more efficient at higher speeds."

Now you're getting it, but you have to apply that same concept to other cars as well, not all but still a substantial amount.

Fine whatever.

I didn't think you had anything to back up your claim.

I grow tired of asking you for information that suport that does not exist.

Table 4.22
Fuel Economy by Speed, 1973, 1984, and 1997 Studies
(miles per gallon)

Speed 1973a 1984b 1997c
(miles per hour) (13 vehicles) (15 vehicles) (9 vehicles)
15 d 21.1 24.4
20 d 25.5 27.9
25 d 30.0 30.5
30 21.1 31.8 31.7
35 21.1 33.6 31.2
40 21.1 33.6 31.0
45 20.3 33.5 31.6
50 19.5 31.9 32.4
55 18.5 30.3 32.4
60 17.5 27.6 31.4
65 16.2 24.9 29.2
70 14.9 22.5 26.8
75 d 20.0 24.8

So tell me again how this proves fuel economy is better at 75 than 55?

Or this...

1997
Speed Toyota
(mph) Celica
5 19.1
10 34.1
15 41.7
20 46.0
25 52.6
30 50.8
35 47.6
40 36.2
45 44.1
50 44.8
55 42.5
60 48.4
65 43.5
70 39.2
75 36.8
Fuel economy loss
5565 mph -2.4%
6575 mph 15.4%
5575 mph 13.4%

Again, if you want to say that you don't want to go less than 75 fine. But don't blow smoke and say that it is more fuel efficient.

When this whole arguement began, I really wanted to know which cars could do this. But it is apparent that it is none.

Now you're getting it, but you have to apply that same concept to other cars as well, not all but still a substantial amount.

So I still want to see a list of what cars this applies for. Everything I have read says that the use of a six speed automatic will 10% increase fuel economy at 55-60 mph, but most of the benefits of the six speed is to decrease the range of each gear up to six in order to make the car shift smoother and have more power in 1st gear.

"But it is apparent that it is none."

From you own example
55 42.5
60 48.4
65 43.5

Oh oh whats that more efficient at 60 and 65 than 55 five? Did you even look?

Now i never said all cars are better at 75 i said my lincoln was and mentioned a few trucks that weren't. But you just proved me right again with the celica how much further are you willing to dig?

And did you notice that table i provided that you posted that there is only a minute difference between 55 and 60 and that includes truck which emphasize the drag effect in far greater proportion than cars.
Go ahead keep proving me right i don't mind at all.