Does fuel economy get better with altitude?
 

Has anyone tried to test if you get better fuel economy at higher elevations? In theory it could have an effect since the air density decreases and you would have less drag. I know aircraft fly at higher altitudes to increase their range. It might be hard to see any difference in a vehicle since you have to control for road and traffic conditions. Plus rolling resistance is a lot of the problem at lower speeds and this doesn't apply to aircraft.

I have not tested it for lack of practical means to do so, but it should have even better benefit in a car than in an airplane.

1. Less air resistance
2. Engine detuned a bit for cruise
3. as for advantage over an airplane, a propeller will "slip" more in thin air whereas a car does not experience such slip.

Regarding aircraft mileage and altitude.

All aircraft engines (reciprocating, turbo-prop & jet) maintain approximately the same air to fuel ratio at all altitudes. As an aircraft climbs there is less O2 air molecules per gulp therefore less fuel is consumed (ratio remains the same). At +/- 18,000 ft. the amount of O2 available is 50% compared to sea level (on a standard day) thus fuel burn decrease approximately 50%.

Less O2 also means less power unless you are turbocharge. Less O2 also means less air meaning less resistance BUT it also means less horsepower, shaft horsepower or (jet thrust) available.

All other thangs being equal, humid air will result in less horsepower because the moisture molecules will displace O2 molecules. This gets into DENSITY ALTITUDE problems, see Density altitude - Wikipedia, the free encyclopedia

If you want really good gas mileage move to Leadville, CO. or Tibet.

Unless you are driving a NA Diesel in which case you will get much worse mileage at higher altitudes and more MPG at lower.

If you are driving a NA Diesel, I doubt if you could get up to Leadville, Co.

bombloader -

There's a dude with a Ford ZX2 that got monster MPG in Colorado at maybe 10K altitude. A lot of his MPG was from empty roads + NHRA background leading to great aeromods. But, I would argue that one component of his MPG came from how his ZX2 reacted to the higher altitude.

CarloSW2

I notice a definite mileage improvement when driving at 2100 ft elevation in the NC mountains when compared to driving at 500 feet elevation in the SC piedmont.

Yes. I got really good gas mileage with a WJ Grand Cherokee at 6000 feet

Aerodynamic drag is some 20% lower in Denver than in Miami. However, there tend to be a lot of annoying hills and mountains at those elevations. Some are steep enough to cause you to waste energy braking, and even small hills interfere with urban planning. I use more gas and drive more miles trying to get around Pittsburgh than Buffalo.

High altitude would be good for fuel economy except for one thing: uphill grades.

Most high altitude terrain I've ever seen is either uphill or downhill, rarely flat.

Remember you road load equation: 20 lb load per ton per percent grade. Entropy assures you never recover all your potential energy coming downhill.


BTW, a 6.2 GM diesel (mine) made it to Leadville and over every pass I tried. I even got the thing to the summit of Pike's Peak - Altitude 14,406 ft.

Caveat: I did have to slow down and it smoked like a steam locomotive.