RC rollout calculator
Distance the car travels for one turn of the motor.
How it works
Rollout is how far the car travels for one turn of the motor:
rollout = (π × tyre diameter) ÷ final drive ratio
A 64 mm tyre rolls 201.06 mm per turn of the wheel, and behind a 7.80:1 final drive that is 25.78 mm per turn of the motor. Leave the ratio out and you get the tyre circumference on its own, which is the same thing as rollout at a 1:1 final drive.
Why racers compare rollout, not gearing
Final drive ratio only describes the gears. Rollout folds in the tyre as well, so it is comparable between two cars that do not share a transmission, and it accounts for something gearing alone misses: tyres shrink as they wear, and a worn tyre is effectively geared lower than the same car was on fresh rubber. Recording rollout alongside your gearing is what makes a setup repeatable weeks later.
Reference values
Rollout in millimetres per motor revolution.
| Tyre diameter | 6:1 | 7:1 | 8:1 |
|---|---|---|---|
| 60 mm | 31.42 mm | 26.93 mm | 23.56 mm |
| 62 mm | 32.46 mm | 27.83 mm | 24.35 mm |
| 64 mm | 33.51 mm | 28.72 mm | 25.13 mm |
| 66 mm | 34.56 mm | 29.62 mm | 25.92 mm |
| 68 mm | 35.6 mm | 30.52 mm | 26.7 mm |