This tool estimates quarter-mile performance using power-to-weight relationships. It converts your inputs to wheel horsepower and pounds, then applies coefficients and optional condition adjustments.
- ET (s) ~= kET × (Weight / HP)^(1/3)
- Trap MPH ~= kMPH × (HP / Weight)^(1/3)
- HP from torque: HP = (Torque(lb-ft) × RPM) / 5252
Condition knobs modify ET and MPH for traction, density altitude, aero penalty, track grade, and shift delay. Use custom coefficients to match your typical tire, gearing, and launch style.
- Choose power input or torque plus RPM mode.
- Select crank or wheel power, then set drivetrain type.
- Enter total weight, or build weight from components.
- Pick a model preset or customize ET and MPH coefficients.
- Adjust traction, density altitude, and optional delay values.
- Calculate, then export results as CSV or PDF.
| Setup | Wheel HP | Weight (lb) | DA (ft) | Traction | Estimated ET (s) | Estimated MPH |
|---|---|---|---|---|---|---|
| Street coupe | 280 | 3200 | 1500 | 0.95 | ~ 13.8 | ~ 101 |
| Daily sedan | 220 | 3600 | 500 | 0.92 | ~ 15.1 | ~ 93 |
| Light hatch | 260 | 2600 | 0 | 0.98 | ~ 13.1 | ~ 104 |
| Prepped drag car | 550 | 3100 | 0 | 1.06 | ~ 10.2 | ~ 132 |
| AWD street build | 420 | 3700 | 2000 | 1.02 | ~ 11.9 | ~ 118 |
1) Power input: horsepower or torque plus RPM
If you only know torque, the calculator converts it using HP = (Torque × RPM) / 5252. Example: 380 lb‑ft at 5250 RPM is about 380 HP. Use a realistic RPM point, not the peak number, for a better average power estimate.
2) Wheel versus crank power and drivetrain efficiency
Wheel power usually predicts quarter‑mile performance more reliably. If you enter crank power, drivetrain efficiency estimates wheel power. Common starting points are 88–92% for FWD, 85–90% for RWD, and 75–85% for AWD. Tune this value using a dyno sheet or known track slips.
3) Weight details that change results
Quarter‑mile ET is sensitive to total race weight, including driver and fuel. In breakdown mode, fuel weight is estimated using typical densities: about 6.17 lb per gallon for gasoline and 7.10 lb per gallon for diesel. A 10‑gallon fuel load can add roughly 62–71 lb.
4) Model presets and custom coefficients
The estimate uses coefficients in ET ≈ kET × (W/HP)^(1/3) and MPH ≈ kMPH × (HP/W)^(1/3). “Street” is conservative, “Race” is optimistic, and “Custom” lets you match your typical setup. If your slips are consistently 0.3 s slower, raise kET slightly.
5) Density altitude: how air changes the run
Density altitude (DA) models air quality. Higher DA usually means slower ET and lower trap speed. A simple rule used here is roughly +1.0% ET per 1000 ft DA and about −0.5% MPH per 1000 ft DA. If you do not know DA, use the compute mode with elevation, temperature, and barometer.
6) Traction factor and measured 60‑ft refinement
Traction mainly affects early acceleration. Use 0.90 for street tires, 1.00 for average, and 1.05+ for a well‑prepped surface. If you have a measured 60‑ft time, enable refinement. The tool shifts ET by about 1.5× the 60‑ft difference, helping your estimate reflect launch and tire limits.
7) Gearing outputs: RPM at trap and redline speed
With tire diameter, rear gear, and top gear, the calculator estimates trap RPM using RPM ≈ MPH × GearTotal × 336 / TireDiameter. This highlights gearing issues such as trapping past redline. If your predicted trap RPM is too high, consider a taller tire, a longer top gear, or a lower rear ratio.
1) Should I enter wheel horsepower or crank horsepower?
Wheel horsepower is usually best because it reflects real delivered power. If you only know crank horsepower, choose crank and set a realistic drivetrain efficiency for your drivetrain.
2) Why is my ET improving but trap speed stays similar?
ET is very sensitive to launch and traction, while trap speed is more tied to power. Better tires, shifting, and a cleaner launch can cut ET without adding much MPH.
3) How do I choose a traction factor?
Start with 0.90 for street tires, 1.00 for average conditions, and 1.05 to 1.10 for sticky tires on a prepped surface. Adjust it until the 60-ft estimate matches your typical runs.
4) What does density altitude do in this calculator?
Higher density altitude reduces effective performance. The tool applies a simple adjustment of roughly +1.0% ET and −0.5% MPH per 1000 ft. Use compute mode if you have weather data.
5) What are kET and kMPH and when should I customize them?
They scale the core power‑to‑weight formulas. Customize them if you want your estimates to match your car’s typical tires, launch, gearing, and aerodynamic drag. Use your track slips to tune.
6) How does the measured 60‑ft option change results?
It nudges ET to better reflect your real launch. The calculator compares your measured 60‑ft to its estimate and shifts ET by about 1.5× the difference, without heavily changing trap speed.