• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

Does driving at 55 use less gas then driving at say 65 or 70?

A

alexjohnson16

Platinum Member
Seems like common sense to me, but one of my friends doesn't believe me...

Anyone have any links that show it does or know how it does?
 
Ive heard that 55mph is the sweet spot for best gas mileage. No sources for that though.

I would assume it has something to do with the RPM's you are driving at.
 
it depends on the car, each car has a sweet spot (RPM) from 55-70 you are usually in your highest gear. and when you are in your highest gear the lowest rpm you can use to stay at that speed will save you the most gas.
 
but you know, a lot of other factors can improve gas usage. like tires, terrain, acceleration decelleration. etc.
 
Not neccesarily .. it depends on the RPM's of the car



Usually 2.5k is the sweetspot.... but it can vary. My car reports MPG


Straight stretches Cruise control


70 mph = 34 mpg with no AC on, 3k rpm
75 mph = 29 mpg with no ac on 3200 rpm
62mph = 37 mpg with no ac on 2500 rpm






 
55mph in 68F was the sweet spot in the 1970's when that became a well known saying. Dunno if that still holds true today. Cars have changed significantly.
 
It depends upon how the car is geared. People will say aerodymanics make a difference but that simply is not true at these speeds from my experience. When I had my 85 GT Mustang the national speed limit was 55. When driving 55 on the highway in 5th gear I would get 25 mpg. The gearing was not optimized on that car because when I drove 70 mph I got 27 mpg.
 
Originally posted by: Ronstang
It depends upon how the car is geared. People will say aerodymanics make a difference but that simply is not true at these speeds from my experience. When I had my 85 GT Mustang the national speed limit was 55. When driving 55 on the highway in 5th gear I would get 25 mpg. The gearing was not optimized on that car because when I drove 70 mph I got 27 mpg.
Click to expand...

I've always heard that each small increase in speed increases wind resistance by an exponential amount. . .
 
Originally posted by: dxkj
Not neccesarily .. it depends on the RPM's of the car

Usually 2.5k is the sweetspot.... but it can vary. My car reports MPG
Click to expand...

Yea probably staying under 3k would be a good idea.
 
Look at the following factors:

RPM
Throttle

Throttle is hard to gauge unless you have a gauge built-in, and almost all cars don't. Just guestimate by using your pedal travel as a gauge. Your mileage goes down the crapper if you try to maintain your speed going uphill because you need to increase your throttle to counteract gravity, even if your RPMs are the same as when you're going downhill.
 
Originally posted by: dartworth
It may, and it probably get some people killed...
Click to expand...
:thumbsup:
I'd rather do 75 (like everybody else on the freeway) and use a little more gas, and NOT get killed...
 
Originally posted by: Koenigsegg
Originally posted by: Ronstang
It depends upon how the car is geared. People will say aerodymanics make a difference but that simply is not true at these speeds from my experience. When I had my 85 GT Mustang the national speed limit was 55. When driving 55 on the highway in 5th gear I would get 25 mpg. The gearing was not optimized on that car because when I drove 70 mph I got 27 mpg.
Click to expand...

I've always heard that each small increase in speed increases wind resistance by an exponential amount. . .
Click to expand...
The drag increases with the square of the velocity. Double the velocity, quadruple the drag.
 
In a vintage 1970s car with a three-speed automatic transmission, it's likely that 55mph does indeed save gas. However, given that my car does 80mph at 2000rpm in 6th gear, I would say that some research would need to be done before anybody could make such a definitive statement.
 
Originally posted by: klah
Here's a graph: http://www.fueleconomy.gov/feg/driveHabits.shtml
Click to expand...

The steep decay curve shown there is BS propaganda used by our gov't to try to justify the speed tax. Both my Escort and my old '83 Bonneville Brougham got in the upper 20s at over 130mph. The Bonneville was a huge tank, bigger than most SUVs and had city mileage in the single digits to teens, yet even that was able to maintain good mileage at high speed. Oh, and neither car would be in high gear at 55, or even 75 for that matter, that is also a load of BS. 75 in the Bonneville would be 2nd gear.

When you take into account the extra horsepower your engine must keep generating for the air conditioning you are in fact probably saving gas by going above the limit to some extent (like say 80 vs. 55 for example) by reducing the amount of time you are in the car with the A/C running.

I'm not saying gas mileage doesn't degrade above a certain speed, it does. Just not close to the extent you are lead to believe.
 
In my 96 Mazda Protege I get 40mpg cruising at 70mph with the AC on. I'm not sure if that's the optimal speed, but I certainly can't complain about the fuel economy.
 
Originally posted by: Howard
Originally posted by: Koenigsegg
Originally posted by: Ronstang
It depends upon how the car is geared. People will say aerodymanics make a difference but that simply is not true at these speeds from my experience. When I had my 85 GT Mustang the national speed limit was 55. When driving 55 on the highway in 5th gear I would get 25 mpg. The gearing was not optimized on that car because when I drove 70 mph I got 27 mpg.
Click to expand...

I've always heard that each small increase in speed increases wind resistance by an exponential amount. . .
Click to expand...
The drag increases with the square of the velocity. Double the velocity, quadruple the drag.
Click to expand...

not true

wind drag is proportional to speed until about 85 km/h depending on the aerodynamics of the car (but it will stay in the 80's)

after that it starts increasing exponentially like you mentioned

 
Originally posted by: coomar
Originally posted by: Howard
Originally posted by: Koenigsegg
Originally posted by: Ronstang
It depends upon how the car is geared. People will say aerodymanics make a difference but that simply is not true at these speeds from my experience. When I had my 85 GT Mustang the national speed limit was 55. When driving 55 on the highway in 5th gear I would get 25 mpg. The gearing was not optimized on that car because when I drove 70 mph I got 27 mpg.
Click to expand...

I've always heard that each small increase in speed increases wind resistance by an exponential amount. . .
Click to expand...
The drag increases with the square of the velocity. Double the velocity, quadruple the drag.
Click to expand...

not true

wind drag is proportional to speed until about 85 km/h depending on the aerodynamics of the car (but it will stay in the 80's)

after that it starts increasing exponentially like you mentioned
Click to expand...

Actually, I believe wind drag IS proportional to speed squared, it's just not the most significant factor until you are moving at a decent clip. Not sure but I think the drag from the tires deforming under the weight of the car (and depending on pressure) is proportional to speed, and that is probably larger than the wind drag factor at and below the speed limit.

 
You must log in or register to reply here.

TRENDING THREADS

Back
Top