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Discussion Starter · #1 ·
Although I didn’t have a lot opportunities to experiment with this on a flat road it seems like 55mph delivers the best fuel mileage.

What have others found to be the ideal speed to get the most mgp?
 

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Discussion Starter · #3 ·
Well, again I haven't played with this very much, but at 55 mph on a level road it seemed my Trip Computer indicated a current fuel consumption of 44 mpg.

I've always heard that certain engines have a "sweet spot" a speed which delivers the best mpg. At one time I had heard big V8 engine got the best mpg in the 50-60 mph range, while smaller 4 cylinder engines would be somewhere below 45 mph.
 

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Just under 70 seems to be a sweet spot for most cars I've owned. "Drive 55" is a fallacy perpetuated by power hungry political types, and does not relate to engine size as much as gear ratios.
 

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basic physics
http://en.wikipedia.org/wiki/Wind_resistance

"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."
 

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lne937s said:
Note that the power needed to push an object through a fluid increases as the cube of the velocity.
I am *definitely* driving a Cube of velocity! LOL! 8) :D

Aerodynamics of a brick! :eek: :yes:

Glad to see we have some more engineering types here. Thanks for including the link to the wiki article.
 

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The Wiki does not account for gearing. If you drive a car that is revving higher or lugging at 55, then you will see a difference altering speed to account for that. My BMW got 33MPG at 68MPH. Any lower or higher yielded worse MPG.
 

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http://cta.ornl.gov/data/tedb28/Edition28_Chapter04.pdf

pages 26-30

Most modern cars tend to get their best mileage ~50-55 miles per hour. Due to the exponential impact of aerodynamic drag as you increase in speed, mileage tops out regardless of your gearing (the higher the gearing, the less engine friction/pumping losses per rotation of the wheels). Now, the point where aero drag takes over will depend somewhat on how much engine pumping/friction you have (generally, a smaller engine pumps a smaller amount of air and has fewer surfaces rubbing together), as well as the aerodynamics of the vehicle. With a car like a cube that has a small engine, large frontal area, and not that aerodynamic of a shape, I would expect the best mileage to be a little less than 55 mph- even with ideal gearing.
 

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Yeah thats why i got a manual for my town car. i can drive 50mph and get
40-43mpg on flat ground in six gear. as long as i dont hit pot holes or red lights i can
go forever.
 

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I tested it again today, drove 80+ miles for a shopping trip, did about half at the speed limit of 60mph on the back roads, and on the way home I did about 75mph on the Interstate, filled up when I got back to town, and got a new record high (for my usually heavy foot) 38 mpg. The trip consisted of a couple big hills but mostly level travel. I have about 3600 miles on my Cube now.
 
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