RPM / Speed / Gear Ratio Visual Calc

This calculator allows you to interactively change the variables that determine your engine's RPM at any given MPH between 0 and 250. You can alter the axle gear ratio, transmission gear ratio, tire height or profile, torque converter efficiency, and see the impact in real-time.

For example, you may wish to know what effect that 4.10 ring and pinion will have on highway cruising speed before you buy it. Or, maybe your speedo is inaccurate and you'd like to know how fast you're really going when the tachometer is at 3,000.

All the transmission and axle ratio fields are dynamic so you can customize them for your car. Drag the floating panels around if they get in your way.



Visual RPM, Speed, and Gear Ratio Calculator
This calculator allows you to interactively change the variables that determine your engine's RPM at any given MPH between 0 and 250. You can alter the axle gear ratio, transmission gear ratio, tire height or profile, torque converter efficiency, and see the impact in real-time. For example, you may wish to know what effect that 4.10 ring and pinion will have on highway cruising speed before you buy it. Or, maybe your speedo is inaccurate and you'd like to know how fast you're really going when the tachometer is at 3,000. All the transmission and axle ratio fields are dynamic so you can customize them for your car. Drag the floating panels around if they get in your way.



Notes: Consult the numbers above the gauges or the readout in the 'your setup' panel for the actual RPM and MPH. The gauges show approximations. 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. 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. The 'estimated 1/4 mile' panel estimates rear wheel 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. For further reading have a look at this page, Calculators for 1/4-Mile ET & MPH vs. HP and Weight.