High altitude fuel economy

[Subaruwagon]

I was just wondering if there would be any noticble difference in fuel economy at high altitudes compared to driving at sea level due to the lack of oxygen meaning less fuel and having to open the throttle more reducing pumping loses? I live at about 700ft so this doesn’t apply to me but I was curious if it makes a real world difference in mpg numbers.

[Ecky]

I don't have any numbers to back it up, but my impression was that it varies from vehicle to vehicle. My Insight, for instance, is already near WOT in most conditions due to its luxuriously tall gearing, so taking it up 10,000ft results in needing to rev it up a lot more, hurting economy. Ditto for cars with CVTs (that have sufficiently wide ratios) or hybrids which can rev the motor independently of wheel speed. Higher powered manuals and automatics should benefit... except that most high altitude driving will probably also be in mountains.

[Hersbird]

Cars or trucks with poor aerodynamics or large frontal area it will help economy with thin air. The problem is it is also usually colder at higher altitude so it probably is a wash. Pilots have to consider such things, it think they use density altitude to figure where they are in relation to standard atmospheric pressure.

[redpoint5]

Generally the gains from fuel economy at altitude are mostly due to lower wind resistance, and less from reduced pumping losses.

Different vehicles will be affected in different ways. A turbocharged vehicle will cope with the thinner air better than a NA vehicle.

[jamesqf]

Originally Posted by Ecky

My Insight, for instance, is already near WOT in most conditions due to its luxuriously tall gearing, so taking it up 10,000ft results in needing to rev it up a lot more, hurting economy.

I've noticed just the opposite: I seem to get better mpg with my Insight at my normal elevations, which run from about 4500 to 9000 ft, than I do near sea level. But it's not really a fair comparison, as the driving is very different. The higher elevations include a lot of climbing and descending mountains, often on twisty roads, and flat stretches tend to have little traffic so I can cruise at economical speed.. Sea level includes a lot of California freeways, which are either bumper-to-bumper or going like a bat out of hell.