Gear Ratio Speed Calculator. With the gear ratios of the transmission and differential, and the size of the tires, it becomes possible to calculate the speed of the car for a particular gear at a particular engine RPM. Features: Calculate theoretical speed for a car for each of its gear ratios. Calculate travel distance for each engine revolution. Use maximum RPM to figure top speed for each gear. Metric or Imperial units for selection. Universal app for both iPhone and iPad. Axle ratio are similar as Final Drive Ratio. If a car has less than 6 gears, only enter the ratios that apply. Note that you will get unreal speeds for overdrive gears. This is because in reality top speed is physically limited by it power or by aerodynamic drag. Thanks for your support and do visit nitrio.com for more apps for your iOS devices.