Rollout Calculator Tire Diameter The diameter of your tire measured from the outer edges Rollout Calculator This calculator will allow you to determine the correct rollout ratio based on just a few inputs. Data Input Results If you do not understand any particular term, just slide your mouse over it for a definition Outer Tire Diameter Spur Gear Pinion Gear Transmission Ratio : 1 (check gear ratios on popular models) A higher rollout number results in slower acceleration and greater top speed. Lower rollout results in the opposite. Tire Circumference Pinion:Spur Ratio Gearing Quotient Rollout Ratio Although this calculator works for most motors, some require different gearing to compensate for heat issues. Always check your motor every few minutes to see if it is getting too hot. With a properly geared motor, you should be able to hold your finger directly in the center of the can for at least 5 seconds. Anything less than that, and you are overgeared. ROLLOUT CALCULATOR FROM RC UNIVERSE.