The area they cover is only about 1-1/2% of your total frontal area. Motorcycles go much faster, and none of those are aerodynamically shaped. I've heard that you have to travel much faster than a bike is capable of, for the aerodynamics to be effective. For example a car has to travel in excess of 140mph for its' "wing" to have any effect. I know 1-1/2% is better than nothing, so why doesn't someone design some type of "body" air foil?