20" Wheel will take away some power but nothing that cannot be made up with a CAI &Tune along with some gears.

Richard

 

wheel size affects gear ratio, not hp. It will take less hp/tq to turn a set of 17" tires and rims than 20" rims and tires that weight a lot more.

Less rotational mass = better

dyno numbers shouldnt change since the vehicle isnt trying to overcome the weight of the car to get going..

 

So why doesn't a stock Mustang dyno at 300 hp? I thought because you lose though the drive train, and wouldn't heavier rims & tire add to the amount lost?

 

Mustangs don't dyno at 300hp because of the parasitic loss of the power being transfered from the engine, through the driveline. Without going into a lot of detail manual transmissions dyno more because STOCK they are more efficent than manual transmissions thus the parasitic loss is reduced to around 10-14%.

06GTW/JUICE is right except for the final statement. "dyno numbers shouldnt change since the vehicle isnt trying to overcome the weight of the car to get going"

If that was true, why do adding a set of 4.10 gears decrease horsepower numbers slightly?

Rims/Tires and gears all affect the parasitic loss, the slight loss in horsepower isn't whats making the car feel so much slower. Well, a small portion of it is, but the speed factor is mostly felt because of the extra rotational weight that the car is forced to turn.