Horsepower from trap speed calculator
Trap speed is a better power estimate than elapsed time, because it depends less on traction and launch.
s
Power from trap speed
11 833.1hp
- In kilowatts
- 8823.9
- Power from elapsed time
- 265.7 hp
- Elapsed time that power predicts
- 3.808 s
- Trap speed in mph
- 357.91
- Power to weight
- 5882.6 W/kg
Show the working
- Vehicle weight with driver = 1500
- Trap speed = 160
- Elapsed time = 13.5
- weight_lb = 1500 / 0.45359237 = 3306.93
- Trap speed in mph = 160 * 3.6 / 1.609344 = 357.91
- Power from trap speed = 3306.93 * (357.91 / 234)^3 = 11 833.1
- Power from elapsed time = 3306.93 / (13.5 / 5.825)^3 = 265.651
- In kilowatts = 11 833.1 * 0.7456998715822702 = 8823.95
- Power to weight = 1500 > 0 ? 8823.95 / 1500 * 1000 : 0 = 5882.63
- Elapsed time that power predicts = 11 833.1 > 0 ? 5.825 * (3306.93 / 11 833.1)^(1/3) : 0 = 3.808 36
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Hale: hp = weight in lb x (trap speed in mph / 234)^3
- Fox: hp = weight in lb / (ET / 5.825)^3
These are empirical fits to drag strip data, not physics. They assume a reasonably typical drag coefficient and a full-throttle run.
The two formulas disagree when traction is poor, because a bad launch hurts elapsed time but not trap speed.