Enter any 2 values (power, estimated trap speed, and vehicle weight) into the calculator to determine the missing variable.
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BHP to Trap Speed Formula (Rule of Thumb)
The following formula is a common rule-of-thumb used to estimate quarter-mile trap speed from power and vehicle weight. It does not predict exact real-world road speed, top speed, or acceleration because aerodynamics, traction, gearing, drivetrain losses, and many other factors matter.
S \approx 234 \times \left(\frac{BHP}{W}\right)^{1/3}Variables:
- S is the estimated quarter-mile trap speed in miles per hour (mph)
- BHP is the brake horsepower (in HP)
- W is the vehicle weight in pounds (lbs) (typically including the driver)
To estimate the trap speed, divide the BHP by the weight, take the cube root of the result, and then multiply by 234.
| Horsepower (HP) | Kilowatts (kW) |
|---|---|
| 50 | 37.285 |
| 75 | 55.928 |
| 100 | 74.570 |
| 125 | 93.213 |
| 150 | 111.855 |
| 175 | 130.498 |
| 200 | 149.140 |
| 225 | 167.783 |
| 250 | 186.425 |
| 275 | 205.068 |
| 300 | 223.710 |
| 350 | 260.995 |
| 400 | 298.280 |
| 450 | 335.565 |
| 500 | 372.850 |
| 600 | 447.420 |
| 700 | 521.990 |
| 800 | 596.560 |
| 1000 | 745.700 |
| 1500 | 1118.550 |
| Conversion used: 1 HP = 0.7457 kW (1 kW ≈ 1.34102 HP). | |
What is BHP?
BHP, or brake horsepower, is a measure of an engine’s power output measured at the engine crankshaft on an engine dynamometer (i.e., before drivetrain losses through the transmission, driveshaft, differential, and tires). BHP is typically expressed in horsepower (HP) or kilowatts (kW). Because real vehicle speed depends on many factors (aerodynamics, gearing, rolling resistance, traction, and drivetrain losses), BHP alone cannot determine an exact road speed, but it is an important indicator of performance potential.
How to Calculate BHP to Speed?
The following steps outline how to estimate quarter-mile trap speed from BHP and weight using a rule of thumb.
- First, determine the brake horsepower (BHP) of the engine (in HP).
- Next, determine the vehicle weight in pounds (lbs) (typically including the driver).
- Then, use the formula S ≈ 234 × (BHP / W)^(1/3) to estimate the quarter-mile trap speed.
- Finally, interpret the result as an estimated trap speed in miles per hour (mph) (or convert units as needed).
- After inserting the values and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Brake Horsepower (BHP) = 300
Weight (W) = 4000 lbs
Estimated trap speed: S ≈ 234 × (300 / 4000)^(1/3) ≈ 98.7 mph