Rollout is used to keep the same final drive ratio as tires wear. If you find the prefect setup with your motor at your home track is a newer tire say 2.25, a 40 pinion and a 120 spur which is a 2.35 rollout. Now you're looking at your tire and its only a 2.14 it will let you know to maintain the prefect ratio you would need to put on a 42 pinion.Q-ball said:Can someone explain what roll-out is to me? This is a new term since I was racing before. I saw how to calculate it, but what is it, and why is it important?