Eighth-Mile ET Calculator

Start with the operating case

Estimate eighth-mile elapsed time from weight and power — the model isolates a performance relationship under stated assumptions.

Short-distance results are particularly sensitive to traction and launch technique — that condition defines when estimated eighth-mile et is comparable with another result.

The mathematical relationship

In “eighth-mile ET ≈ 3.73 × (weight ÷ horsepower)^(1/3) × launch factor,” the calculation does not infer a missing vehicle measurement.

No term beyond race weight, wheel horsepower, and launch correction is introduced in “eighth-mile ET ≈ 3.73 × (weight ÷ horsepower)^(1/3) × launch factor.”

Building one consistent data set

The Race weight entry represents vehicle, driver, and fuel weight — before calculating, use the same loaded condition for every weight and retain the scale ticket or rating source.

Wheel horsepower: Power delivered to the wheels — a compatible entry should identify whether the reading is taken at the source, charger, battery, or accessory.

Launch correction. Multiplier for traction and shift performance — for this measurement, use a measurement or specification from the exact component and operating condition being evaluated.

Meaning of the calculated value

Estimated eighth-mile ET answers “Estimate eighth-mile elapsed time from weight and power.” The additional displays, Idealized eighth-mile ET and Weight per horsepower, are a different view of the same entered measurements.

Use controlled facilities rather than public roads — when that condition changes, compare separate calculator runs instead of blending the inputs.

Because short-distance results are particularly sensitive to traction and launch technique, a disagreement between estimated eighth-mile et and an outside reference should trigger a review of race weight and launch correction.

This page does not attempt to calculate theoretical road speed at an engine-speed limit — the Gear-Limited Top Speed provides that calculation.

What remains a separate check

Traction, grade, wind, temperature, driver input, and control-system intervention remain outside this simplified model — for launch correction, the page specifically expects multiplier for traction and shift performance.

If your notes raise the question of how to estimate rolling resistance force and power from vehicle weight and a coefficient, move to the Rolling Resistance without changing this page's inputs.

Recording the operating setup

Choose a controlled operating condition and record the setup before comparing a second run — this workflow must also account for the fact that short-distance results are particularly sensitive to traction and launch technique.

• Record Race weight as vehicle, driver, and fuel weight — use the same loaded condition for every weight and retain the scale ticket or rating source.
• Record Wheel horsepower as power delivered to the wheels — identify whether the reading is taken at the source, charger, battery, or accessory.
• Record Launch correction as multiplier for traction and shift performance — use a measurement or specification from the exact component and operating condition being evaluated.
• Repeat the check only after accounting for this condition: short-distance results are particularly sensitive to traction and launch technique.

What the shorter distance emphasizes

An eighth-mile elapsed time places more weight on launch, early traction, shift execution, and the first half of the acceleration curve than a quarter-mile result. A vehicle that gains strongly at higher speed may therefore look less competitive in the shorter interval than its later acceleration suggests.

Quarter-mile projections from an eighth-mile pass are empirical, not a continuation guaranteed by the calculator. Gear changes, thermal limits, aerodynamic drag, and power falloff can alter the second half. Preserve the sixty-foot time and eighth-mile speed with the elapsed time so a later comparison can distinguish launch improvement from added high-speed power.

Use the timing-slip segments

The sixty-foot, 330-foot, and 660-foot numbers show where an elapsed-time change occurred. Improving the launch can lower eighth-mile time without changing engine power, while a stronger 330-to-660 segment can indicate improved acceleration after traction is established.

Compare slips with the same staging method and lane conditions. A single total elapsed time hides wheelspin, a missed shift, or a late power reduction that the intermediate segments can expose.

Surface and staging consistency

Track preparation and staging depth can move a short-distance elapsed time without any vehicle modification. A deeper stage shortens rollout, while changing tire temperature or burnout procedure can alter the first sixty feet.

Record lane, staging method, tire pressure, and surface condition with each run. When those details differ, the calculator can compare numbers but cannot attribute the change to power, gearing, or traction alone.

Interpreting this calculator