strx7 wrote:that diff ratio gives 25% more applied torque at the wheels and it accelates like you have 25% more torque. perhaps it wont gain 15mph but it would sure gain, and it sure as hell wouldn't go slower.
If it gives 25% more torque, then it does so at a proportionately lower speed. Cant break the rules of horsepower unfortunately!
At a particular vehicle speed, the maximum torque at the wheels is acheived by having the gearing set to run the engine at the rpm which gives max HP.
Either side of this, you can only make as much torque as dictated by the reduced amount of horsepower than the engine makes at that rpm.
If there was a constantly variable transmission which could hold the engine rpm at peak horsepower and vary the vehicle speed, then changing tire size, final drive or anything else would not make any difference to accelleration. (Apart from increased drag etc)