chuckb

Did anyone see the show on speedvision,where they dynoed a car before and after a BBK kit and even though the new rotors where lighter, they lost like 7 or 5 WHEEL HORSEPOWER?

They said it's because the rotating mass is farther away from the center. So this must also apply to larger wheels, even if they are lighter.

mmarshall

It also stems from the fact that many disc brakes have a very slight amount of pad-to-rotor contact even with no foot pressure on the brake pedal. They are adjusted at the factory that way and that is normal. It does not cause a significant amount of wear or heat but is just enough to keep water out....one reason why disc brakes don't lose effectiveness when wet. However, a larger rotor, caliper, and pad contact area obviously will create more friction and draw more engine HP to overcome that friction.....even if, as you say, the brake components themselves are lighter.