What is the optimal speed to drive on a highway for good gas mileage?

[JVS]

I remember reading of 35mph being the WWII speed limit in order to conserve gas. It probably varies from car to car, so for the sake of argument let's just use a current Honda Civic with the standard v cylinder engine as a point of reference. Anyone have any thoughts?

[Elad]

1. 55 mph

http://www.fueleconomy.gov/feg/driveHabits.shtml

[ewagner]

3. I agree

I was always told that engines were designed for their maximum efficiency at 55mph. I don't know if engines have been "tuned" to operate more efficiently at higher speeds.

[cheezus]

2. it's more about RPMs than speed

keep the rpms as low and steady as possible

[trotsky]

4. That's what I've heard.

Highest gear + lowest RPM = best mileage.

[ewagner]

6. Question

If a 6-cylinder is turning 2250RPM at 55 mph and an 8-cylinder is operating at 1500rpm at 55MPH , then is there much difference in fuel consumption?

8-cylinders displace more but operate at lower rpms.....

[cheezus]

9. both trains get to st. louis at 3:30pm

sorry. I don't mean to be an ass, but that just struck me as funny for some reason.

[ewagner]

10. LOL

It occurred to me that it might look like one of THOSE questions right after I posted it.........

What the hell...this is DU......if you can't be a smartass here where can you?

[cheezus]

11. that's a good question

What the hell...this is DU......if you can't be a smartass here where can you?

[bif]

5. 10 MPH

[tech3149]

7. depends on the vehicle and terrain

I get 40mpg in my 98 Civic 5 spd with avg speeds of 55-65mph. That's average around town/ highway mix. Much of the savings come from modest acceleration and anticipating traffic. The rest comes through coasting as much as possible and keeping the speed up to avoid downshifting.
Of course traffic and police have an adverse effect.

[Worst Username Ever]

8. Todays cars designed with 55 mpg in mind

Every 5 miles an hour over 55 is the equivalent of spending an extra 10 cents per gallon in gas.

[Hell Hath No Fury]

12. The correct tire pressure is just as important....

as how fast you drive for good mileage. Underinflated tires create drag that can decrease your fuel efficiency. :)