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Oct14-09, 07:11 AM
P: 52
Calculating driving force from wheel rpm, wheel radius and engine power

Thanks for your replies guys.

I suppose I should have stated that I need to eliminate torque from the equation. This is because the force needs to be calculated from a Power vs. engine rpm curve. I have no direct information on the engine torque so it needs to be calculated from the power (P=Tw).

Converting engine rpm to wheel rpm is simple enough (multiplying by the gear ratio). Acceleration does not really need to be calculated, it was just to check if my equation for force was producing sensible answers.

I cancelled the 2/60 part of the equation to give 1/30 and eliminated T by using T=Fr. Is this right and does then then mean that my equation is in fact technically correct and producing correct answers? Doesn't 1.5ms-2 for a car's maximum acceleration seem a bit slow to anyone? The data I used was a max power of 124kW at 5900rpm (engine rpm) and a 1st gear ratio of 2.92:1 producing a wheel rpm of 2021rpm and according to my equation, 2197N of driving force. The wheel radius is 0.2667m.

Thanks again

Paul H