Formulas, Sources & Accuracy

Quarter-mile ET and trap speed

Primary estimate (Patrick Hale constants): ET = 5.825 × (W ÷ HP)1/3, MPH = 234 × (HP ÷ W)1/3. Conservative variant (Huntington): ET = 6.290 × (W ÷ HP)1/3, MPH = 224 × (HP ÷ W)1/3. W is race weight in pounds including the driver and HP is crank horsepower. These constants and the Fox variants (6.269 / 230) are listed on Stealth316’s horsepower / ET / MPH calculator notes. The same equations appear on other independent calculators such as Omni Calculator.

Inverse equations

HP = W × (5.825 ÷ ET)3, HP = W × (MPH ÷ 234)3, W = HP × (ET ÷ 5.825)3.

Eighth-mile conversions

1/4-mile ET ≈ 1/8-mile ET × 1.56. 1/4-mile MPH ≈ 1/8-mile MPH × 1.25. These are drag-racing rules of thumb quoted on the same Stealth316 page.

0–60 mph model

t = K × (W ÷ HP)0.8 with K = 0.70 (AWD), 0.76 (RWD) and 0.80 (FWD) from Calculator Academy. The 0–100 km/h figure multiplies by 1.05 (our approximation) and the tire factors on the 0–60 estimator (1.05, 1.00, 0.95, 0.90) are our own rules of thumb.

Drivetrain loss and unit constants

Splits on the dragstrip calculator

60 ft ≈ 15% of ET, 330 ft ≈ 42%, 1,000 ft ≈ 85%. These are rough proportions chosen from typical slips and are not from a published standard.

Accuracy

The equations describe a car with good traction, correct weight and measured crank horsepower. Weather, tire, gearing, shifts and driver all move real results. For a 3,500 lb, 400 hp car the primary estimate is 12.00 s / 113.6 mph and the conservative one is 12.96 s / 108.7 mph. Real runs in this class often fall inside that spread. Nothing on this site is a guarantee.

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