| Horsepower | Trap Speed |
|---|
What Trap Speed Tells You
Trap speed is how fast a car is travelling at the end of the quarter mile. Because it is reached after the launch is over, it depends almost entirely on power-to-weight rather than traction or technique. That makes it the single best track number for estimating real horsepower, which is why tuners trust a trap speed over a dyno claim.
The Power-to-Weight Link
Trap speed rises with the cube root of horsepower divided by weight, so it takes a big power gain to move it much. Doubling power does not double trap speed; it raises it by about 26 percent. The same math runs in reverse, letting you back-calculate horsepower from a measured trap speed and the car’s race weight.
Trap Speed Versus Elapsed Time
Elapsed time rewards a clean launch and good gearing, so it is sensitive to traction and driver skill. Trap speed strips most of that away and exposes the engine. A car with a great sixty-foot time but a modest trap is winning on the launch; a strong trap with a weak ET is leaving time on the table off the line.
Frequently Asked Questions
Should I use wheel or crank horsepower?
The formula is calibrated to flywheel horsepower. If you only have wheel horsepower, add roughly 12 to 15 percent for a typical drivetrain to approximate crank power.
What weight do I enter?
Race weight, meaning the car plus fuel plus driver as it crosses the line. Using curb weight alone will overstate trap speed slightly.
How accurate is the estimate?
For most street and strip cars it lands within a couple of mph. Heavy aero, very high speeds, or unusual gearing can widen the error.