Quote:If a bare a$$ed cyclist (I mean pedal) needs 3/4 HP to sustain 55 mph. Why does a motorcycle need so much more to go 70-80 mph. I had VW van, can't of had more than 30 HP, I could easily do 70-80 anytime but uphill.
Drag is a funny thing. A bare cyclist has a much better coefficient of drag (Cd) and less frontal area than a motorcycle. Actually, a VW van has a much better Cd than a motorcycle but more frontal area, so apparently those two things cancel out (roughly). A really aerodynamic car (Cd~.3) and relatively small frontal area only needs between 8 and 12 hp to maintain 55 mph, however it may need about 18 hp to maintain 65 mph.
I've posted the equation somewhere on here before, but basically drag is a function of Cd, frontal area, and velocity squared. Cars have a definite advantage in the Cd department, while motorcycles have an advantage with frontal area. However, the equation gives only an approximation, but actual testing is the only accurate method.
If you remember some of the first motorcycle speed trials, the rider wore a speedo and pointy helmet and laid on the bike with his feet straight out the back. Looked funny, but improved Cd and decreased frontal area...