⚙️ Rollout
How far the car rolls forward for one full turn of the motor — the true measure of gearing.
Rollout = (π × tire diameter) ÷ final drive ratio. Lets you compare gearing across different cars and tire sizes.
What it actually does
Rollout is how far the car travels for one full turn of the motor, and it is the only fair way to compare gearing between cars. Two cars with identical FDR but different tyre sizes are not geared the same, and rollout is what exposes that.
In practice
Rollout = (π × tyre diameter) ÷ final drive ratio, usually quoted in millimetres. Because it folds tyre size in, racers use it to carry a known-good setup from one track or tyre choice to another instead of starting from scratch.
Worth knowing
Tyres grow at speed and wear down over a run, so rollout is not fixed. Measure with the tyres you are actually racing on rather than the box figure.