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Estimate Your Horsepower!
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*.
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*Note:  Assuming a 20% drive train loss.

Calculate HP from ET

Vehicle weight in pounds (including driver)
lbs
1/4 mile 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
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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.
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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
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