How to Measure Gear Ratio

A vehicle's gear ratio describes how much one gear increases another's speed. The measurement is one of several metrics people use to compare vehicles. It determines your car's acceleration, and it affects fuel efficiency. One way to calculate gear ratio involves comparing the number of teeth on connected gears, but you don't need that data. Instead, calculate the gear ratio using your engine specifications. The gear ratio relates the gear's speed to your car's speed, taking into account the size of the vehicle's wheels.

• 1

  Multiply the car's speed, in miles per hour, by 1,056. For example, if your car travels at 50 miles per hour: 50 x 1,056 = 52,800 inches per minute.

• 2

  Divide the answer in Step 1 by pi: 52,800/3.14159 = 16,807.

• 3

  Multiply the figure from Step 2 by 0.5: 16,807 x 0.5 = 8,403.

• 4

  Divide the figure from Step 3 by the radius of the tire. For instance, if your tire's radius is 8 inches: 8,403/8 = 1,050.

• 5

  Divide the vehicle's engine speed by the figure in Step 4. If your engine runs at 4,500 revolutions per minute: 4/500/1,050 = 4.29. This figure is the gear ratio.