Quarter-Mile ET & Trap Speed Calculator

Kinetic energy grows with speed squared and the car must accumulate it over a fixed distance in shrinking time: working through the physics, ET ∝ (W/P)^(1/3). Concretely, a 3600-lb car gains a full second going 300→450 hp, but only ~0.55 s going 450→675 hp — the same 50% power increase. That's also why weight is 'free' ET at every power level: 100 lb is worth roughly 0.1 s on a 12-second car.

With genuine traction (drag radials or slicks, decent 60-foot), within a tenth or two and a couple mph. Diagnostic gaps: trap speed matches but ET is slow → traction/launch problem (check the 60-foot time); both fall short → the power figure was optimistic or density altitude is high; ET matches with low trap → very effective launch masking modest power. The pair of numbers diagnoses a car better than either alone.

NHRA requires a roll bar at 11.49 or quicker (11.00 in convertibles) and a full cage at 9.99; faster than 13.99 in many classes wants a helmet anyway. Tire-wise: above ~400 hp in a RWD street car, regular all-seasons will spin into the prediction gap; drag radials typically buy back 0.3–0.5 s of it. If this tool says 11.20, budget for the bar before the next power part.

Roughly 1% of power per 1000 ft of density altitude for NA engines (turbos compensate partially) — a 5000-ft DA summer day turns a sea-level 12.50 car into a 12.90 car with 3–4 mph less trap. Tracks post DA on race day precisely because racers correct their expectations with it. Enter sea-level-corrected power on a bad-air day and the slip will read slower than this page; that's the air, not the formula.