RPM Calculator, tire height calculator, gear ratio calculator

Why would you want to re-gear your vehicle? Read our article.
RPM Calculator

Enter ratio, tire height and mph then click Solve to calculate RPM
ratio tire height mph  
auto* AOD* manual* 5 speed*
* auto = D in an AOD
* AOD is calculated at .70 transmission ratio
* manual = 4th in a 5 speed
* 5 speed is calculated at .80 transmission ratio

recommended RPM @ 60mph
4 cyl 2200-3200
6 cyl 2000-3000
small block 1800-2800
big block 1600-2600
GM diesel 6.2L 1800-2800
Ford diesel (non-turbo) 1600-2500
Ford diesel (turbo) 1400-2200
Dodge diesel 1400-2200
For specific transmission ratio
r&p ratio tire height MPH trans ratio

Tire Height
Enter tire width, aspect and wheel, then click solve to calculate tire height.
width aspect wheel  
  tire height:

Street tires are rated using three numbers for example 225/70R15 or 255/70/15. In our example 225 is the Width in mm if the tire was measured from the bottom of bead to bottom of bead. In our example 70 is the Aspect, which means that the sidewall is 70% as tall as the tread is wide. In our example 15 is the the Wheel, the size of the wheel in inches, also called rim size. Placing the example numbers in the corresponding fields you will get a Tire Height of 27.4. Place your corresponding numbers into the fields below to calculate your tire height.
Gear Ratio
Enter the number of teeth on the ring & pinion gears then click the solve button
ring gear pinion gear  
  gear ratio: