Calculator Inputs
Example Data Table
| Race Weight | Wheel HP | Traction | Density Altitude | Estimated ET | Estimated MPH |
|---|---|---|---|---|---|
| 3200 lb | 450 hp | 96% | 0 ft | 7.18 s | 96.4 mph |
| 3500 lb | 500 hp | 94% | 1500 ft | 7.16 s | 96.8 mph |
| 2800 lb | 375 hp | 98% | -500 ft | 7.09 s | 97.7 mph |
Formula Used
This calculator uses common drag racing estimate formulas. Real track results can vary because of launch quality, tire compound, suspension setup, weather, shift speed, and surface prep.
Effective HP = Wheel HP × Air Factor × Traction Factor × Gearing Factor Air Factor = 1 - (Density Altitude × 0.00003) 1/8 Mile ET = 3.825 × (Race Weight ÷ Effective HP)^(1/3) - Rollout 1/8 Mile MPH = 185 × (Effective HP ÷ Race Weight)^(1/3) Required Effective HP = Race Weight ÷ ((Target ET + Rollout) ÷ 3.825)^3 Converted 1/8 ET = Quarter Mile ET × 0.655 Converted 1/8 MPH = Quarter Mile MPH × 0.805
How To Use This Calculator
- Select the calculation mode that matches your goal.
- Enter race weight, including driver and fuel.
- Enter horsepower and choose wheel or engine power.
- Add drivetrain loss if engine horsepower is selected.
- Adjust traction and gearing efficiency for your setup.
- Enter density altitude for weather and air correction.
- Use target ET when estimating required horsepower.
- Press the calculate button to view results above the form.
- Use CSV or PDF buttons to save your result.
About 1/8 Mile ET Planning
Why ET Matters
The eighth mile is short, but it is very demanding. A small launch error can change the full pass. This calculator helps compare power, weight, traction, and air. It gives a structured estimate before track testing. It is useful for bracket racers, test teams, and builders. You can model a mild street car or a serious drag setup.
Power And Weight
Race weight is one of the strongest ET drivers. Removing weight usually helps every part of the run. More power can also reduce elapsed time. Yet power only helps when the car applies it well. Wheel horsepower is often better for estimates. Engine horsepower needs a drivetrain loss adjustment. This page supports both methods.
Traction And Setup
Traction decides how much power reaches the surface. A car with weak grip may run slower than expected. Suspension, tire pressure, track prep, and gearing matter. The traction and gearing fields act as correction tools. They help make the estimate more realistic. Use lower values for spinning or poor launches. Use higher values for strong, repeatable passes.
Air And Rollout
Density altitude changes available power. High density altitude usually slows the car. Good air can improve power and speed. Rollout can also change the displayed elapsed time. This calculator lets you include rollout as seconds. Reaction time is shown separately. It does not normally change official ET. It does affect total lane time.
Using The Results
Treat every result as an estimate. Compare several scenarios before making changes. Save each setup with the CSV option. Export a PDF for notes or shop records. Then test at the track. Real data should guide final tuning decisions.
FAQs
What is a 1/8 mile ET?
It is elapsed time for an eighth mile drag pass. It measures the vehicle only after the timing system starts.
Does reaction time affect ET?
Reaction time usually does not change official ET. It affects total race lane time and head-to-head results.
Should I enter engine horsepower or wheel horsepower?
Wheel horsepower is preferred because it reflects drivetrain loss. Engine horsepower can still work if the loss percentage is realistic.
What does traction efficiency mean?
It estimates how well available power reaches the track. Lower values represent wheel spin, poor launch control, or weak surface prep.
Why include density altitude?
Density altitude estimates air quality. Higher values reduce available power. Lower values can improve power and trap speed.
Can this calculator predict exact race results?
No calculator can guarantee exact results. Track prep, driver skill, tire condition, gearing, and weather can change every pass.
How is quarter mile converted to eighth mile?
The calculator multiplies quarter mile ET by 0.655. It multiplies quarter mile speed by 0.805 for a common estimate.
Why is rollout included?
Rollout represents the small movement before timing begins. Different staging habits can change displayed elapsed time slightly.