What would be the speed at which one could get the BEST gas mileage from

[raccoon]

a car? Forget realities for a while, such as: speed limits, in some places if you go too slow you'll get run over, etc.

I know going too fast--once you get over about 50 decreases it, but I've also heard going REAL slow isn't that great either.

[Orsino]

1. Looks as though there can be more than one sweet spot for a given model.

http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles
"Fuel economy at steady speeds with selected vehicles were studied in 1973, 1984, and 1997. The most recent study <10> indicates greater fuel efficiency at higher speeds than earlier studies; for example, some vehicles achieve better mileage at 65 than at 45-mph<11>, although not their best economy, such as the 1994 Oldsmobile Cutlass, which has its best economy at 55 mph (29.1 mpg), and gets 2 mpg better economy at 65 than at 45 (25 vs 23 mpg). All cars demonstrated decreasing fuel economy beyond 65 mph (105 km/h), with wind resistance the dominant factor, and may save up to 25% by slowing from 70 mph to 55 mph.<12>, although high speed roadways represent only a fraction of overall driving, for some drivers."

[mainegreen]

4. The Olds Cutlass gets ~50mpg?

:wtf:

This thing?



I'm ... dumbfounded. And dubious.

Very dubious.

[Orsino]

5. If you're able to drive it at a set speed, apparently...

...and never brake or accelerate. There are very few places, though, where one can drive at 27 mph for any great distance.

[mainegreen]

6. I guess that's why old people in Florida love it.

27mph without speed changes on a flat surface is their thing.

[Orsino]

12. And keeping the left blinker on uses a negligible amount of fuel...

...when you consider those savings.

[Sanity Claws]

20. but what about the drag caused by the seat belt hanging out

the door?

[appal_jack]

10. The 50+ mpg blue line is the Toyota's

The Toyota Celica is an efficient little car. OTOH, the Olds' blue line is the one that barely approaches 30 mpg at its peak.

-app

[mainegreen]

11. Ooooh. Well, that makes a heck of a lot more sense.

[appal_jack]

15. consider it dubiousness rewarded

do be do be doooo...

-app

[Orsino]

13. D'oh!!!

So it is.

[TZ]

2. I think 55 is supposed to be pretty good actually

I think one of the reasons the national speed limit was set at 55 originally was because that was a pretty gas efficient speed....IIRC, the national speed limit was created in the 1970's during the energy crisis

[DarkTirade]

3. Depends on the car and the terrain.

I've only driven two cars that have a 'this is your gas milage RIGHT THIS SECOND' gauge. One of 'em was a big honkin' van. The other was a tiny little hybred. The van's sweet spot was between 45 and 50 on flat ground. I don't know what the hybred's is, because now I live in an area that actually has topography. So you're constantly having to accelerate or decellerate just to keep at the same speed. :P

[SacredCow]

7. Very dependent on the car....

My current ride (4 cyl, manual tranny, 145 hp, compact) has a sweet spot in the 55 to 60 mph range. My previous car (6 cyl, Auto, 195 hp, midsize) was better at 70 mph, strangely enough.

[trotsky]

8. It is generally the lowest RPM at which you can stay in the highest gear.

So yeah, that's going to vary from car to car.

[LostinVA]

9. It depends on the car -- mine is 57 miles an hour

[NJmaverick]

14. I have always used the 30 - 50 MPH range

I think a speed range is more helpful than an exact speed, which varies from vehicle to vehicle.

[billyskank]

16. Probably at the engine RPM that gives peak torque

In top gear, natch.

[mwooldri]

17. There is one speed that is guaranteed to save you gas.

ZERO miles per hour. I guarantee that a turned off engine at this speed will save you near enough 100% of the fuel you purchase.

But assuming that you actually want to drive the car, you'll need to use some gas. As I figured the so-called sweet spot is the lowest RPM at the highest gear.

For my Ford Focus, about 42mph is it.

Mark.

[NoGOPZone]

18. For most vechicles, its somewhere between 40 to 60

The graph shown in the first reply and the govt document it is based on are good reading. This article also is worth viewing.

http://auto.howstuffworks.com/question477.htm

On edit: If you're really want to learn about the topic, read about Brake Specific Fuel Consumption.

[Sanity Claws]

19. Over 35 but less than 60

I have an automatic and it shifts into highest gear at around that point. The higher the gear, the less gas you use. (If this is wrong, please let me know.)
My guess, based on the mileage I got on two automatic cars, is 50 to 55.