Gear Ratio Calculator

Notes:

1.Consult the numbers above the gauges or the readout in the 'your setup' panel for the actual RPM and MPH. The gauges show approximations.

2.The torque converter efficiency calculation is a bit rudimentary. The revs are adjusted up or down based on the percentage set with the slider control.

3.The default transmission and axle gear set ratios are for a 1968 Mopar B-body, e.g., Dodge Charger, with an A833 4 speed or 727 Torqueflite automatic, and an 8 3/4 axle. The tachometer shown is the famous Tic-Toc-Tach, also from a 1968 Mopar.

4.The 'estimated 1/4 mile' panel estimates HP using weight and MPH, then estimates an elapsed time. Decreasing the weight will not lower the ET; it will decrease the horsepower variable used to calculate the ET and you'll get the same number. Have a look at my 1/4 Mile ET, HP, and MPH Visual Calculator for a much more detailed look into the subject.

The formula used for determining RPM given MPH, axle gear ratio, transmission gear ratio, and tire size is the following:

mph X 336.1524 X final drive ratio ÷ tire diameter

Or, the un-simplified long version:

mph X 12 (inches per foot) X 5280 (feet per mile) X axle gear ratio X transmission gear ratio __________________________________________________________________________
                          pi (3.14159265) X tire diameter X 60 (minutes per hour)

Credit to vexer.com for the calculator.