M&H Drag Tire Rollout (Circumference) Measuring Procedure Roll out is the number of inches the tire rolls before it has traveled back to its initial starting point. Measurement Procedure: 1. Once tire is mounted to wheel inflate to 20 PSI and then start deflation. 2. Once tire reaches race pressure (10 PSI for big tires and 12 PSI for small tires) use ¼” wide measuring tape and place it around center of the tire. 3. If they are within 1/2" of each other the tires are a match; if you wish to get them closer take the smaller one back up to 25 PSI let sit for one minute; deflate and measure again. 4. If tires are ¾” or more off in circumference they will need to be swapped out.