This calculator estimates your quarter mile elapsed time (ET) when given the weight of the car and flywheel or wheel horsepower. A 17% driveline loss is assumed for flywheel HP.

Calculate HP from Trap Speed

Vehicle weight in pounds (including driver) lbs

Trap speed at end of 1/4 mi in m.p.h. m.p.h.

You are making : HP at the rear wheels and HP at the flywheel*. JavaScript must be enabled in your browser for the calculation to work.

*Note: Assuming a 20% drive train loss.

Calculate HP from ET

Vehicle weight in pounds (including driver) lbs

ET in seconds sec

You are making : HP at the rear wheels and HP at the flywheel*. JavaScript must be enabled in your browser for the calculation to work.

*Note: Assuming a 20% drive train loss.

Calculate Tire Diameter

Tire width - Series - Wheel Diameter
Example 275 - 60 R 15

Tire Width

Tire Series

Wheel Diameter

Tire diameter in inches
JavaScript must be enabled in your browser for the calculation to work.

Calculate mph for RPM range

Tire diameter

Gear Ratio

This calculation assumes the car's transmission is in drive or 1:1 ratio, no overdrive. For Overdrive cars mutliply the overdrive ratio times the rear and gear ratio. Example a 700R4 transmission has an overdive ratio 0.7:1. For a 4.11 rear end multiply 4.11 x 0.7 = 2.877. Enter 2.877 as the number for the gear ratio to calculate speeds in overdive.
JavaScript must be enabled in your browser for the calculation to work.

1000 rpm

mph

4500 rpm

mph

1500 rpm

mph

5000 rpm

mph

2000 rpm

mph

5500 rpm

mph

2500 rpm

mph

6000 rpm

mph

3000 rpm

mph

6500 rpm

mph

3500 rpm

mph

7000 rpm

mph

4000 rpm

mph

7500 rpm

mph

Calculate Rear End Gear Ratio

Enter the tire diameter in inches, rpm's of the motor at a certain speed as indicated by your speedometer in mph. This calculation assumes the car's transmission is in drive or 1:1 ratio, no overdrive.

Tire Diameter (in)

RPM

Speed at RPM (mph)

Rear End Gear Ratio JavaScript must be enabled in your browser for the calculation to work.