RPM Range Computation By Bowling & Grippo

The following simple computation determines engine RPMs at interval MPH, Tire diameter, final (differential) gear ratio, and transmission ratio (usually 1.0 for high gear, or something like 0.7 for overdrive). Additionally, a tire growth factor is included, which alters the tire diameter by factor times MPH squared, useful for racing slicks. A growth factor of zero removes the "growth" influence.

Also, for automatic transmissions, there are torque convertor "slippage" factors which help account for RPM "loss" through the transmission. These are entered as two sets of transmission efficiency values (percent) at given RPMs, which are linearly interpolated. Remember, this effect RAISES the RPM, because the engine must turn faster to compensate for the losses.

Program Inputs:

Final Gear Ratio:

Transmission Gearing Ratio:

Tire Diameter in Inches:

Tire Growth Factor in Inches Per MPH Squared:

Transmission Slip Factors:

Transmission Efficiency(%) at a RPM of

Transmission Efficiency(%) at a RPM of

MPH Range Minimum:

MPH Range Maximum:

MPH Range Increment Step Size:

Press this button to submit a computation: .

To reset the form input: .

Bruce A. Bowling
Al C. Grippo