Rollout is a measurement that helps calculate gearing. It is something that is used primarily for foam tire setups, but can be applied to rubber tire setups, also.
Rollout is defined as the distance a vehicle moves forward per revolution of the motor. It can change due to tire wear or a tire size. Rollout is measured using this equation:
Tire Circumference x Transmission Ratio x (Spur x Pinion) = Final Drive
Your Rollout depends on your tires circumference. You can calculate the circumference by doing the math: Tire Diameter x 3.14 = Circumference (oh boy….math!)