Re:Winter chills limit range of the Tesla Model S electric car
by Someone on Sunday February 17, 2013 @03:47AM
(#5234624)
Aerodynamics and engine/drive train design.
Aerodynamically, the slower you drive, the more efficient you drive. The exact curve will depend on air pressure, amount of moisture in the air, etc.
For the engine, it is more complicated. You will want to keep its temperature and rpm at ideal levels. rpm and the gearing in the drive train determine what speed(s) that corresponds to (I guess drive train losses will depend a bit on the gearing, too, but that effect should be minimal)
For the two combined, this gets really complicated. Do you drive at the engine-optimal 45 or does the gain due to lower speed offset the loss in engine efficiency at 44? If 44 is more efficient now, will it stay that when it starts to rain? When you enter a different road surface? When your tires heat up and tire pressure increases slightly? When you have a window open?
Aerodynamically, the slower you drive, the more efficient you drive. The exact curve will depend on air pressure, amount of moisture in the air, etc.
For the engine, it is more complicated. You will want to keep its temperature and rpm at ideal levels. rpm and the gearing in the drive train determine what speed(s) that corresponds to (I guess drive train losses will depend a bit on the gearing, too, but that effect should be minimal)
For the two combined, this gets really complicated. Do you drive at the engine-optimal 45 or does the gain due to lower speed offset the loss in engine efficiency at 44? If 44 is more efficient now, will it stay that when it starts to rain? When you enter a different road surface? When your tires heat up and tire pressure increases slightly? When you have a window open?
http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles#Spe... shows how convoluted this can get.