05-20-2008, 06:48 PM
Reported gas mileage improvements in this thread suggest a reduction in gas usage at 65 mph to 80% - 85% of the usage at 75 mph.
At higher speeds wind resistance, aka aerodynamic drag becomes the dominant force, but not the only force, a car must overcome to maintain a constant speed. Wind resistance is equal to a constant x speed x speed, where the constant is a function of a cars shape and the local air density.
Plugging and chugging shows there is 75% as much aerodynamic drag to overcome at 65 mph compared to 75 mph, i.e., 0.75 = (65 x 65) / (75 x 75), which compares fairly well with the 80% - to 85% reported in this thread.
"Should it be voluntary or should we clamp down interstate speeds again? Not that many actually observe a posted highway speed limit."
IMHO - Voluntary
At higher speeds wind resistance, aka aerodynamic drag becomes the dominant force, but not the only force, a car must overcome to maintain a constant speed. Wind resistance is equal to a constant x speed x speed, where the constant is a function of a cars shape and the local air density.
Plugging and chugging shows there is 75% as much aerodynamic drag to overcome at 65 mph compared to 75 mph, i.e., 0.75 = (65 x 65) / (75 x 75), which compares fairly well with the 80% - to 85% reported in this thread.
"Should it be voluntary or should we clamp down interstate speeds again? Not that many actually observe a posted highway speed limit."
IMHO - Voluntary