Sands, thanks for the tip.
Originally posted by sands
If you are on rubber tires, just go with the gear ratio that people use at your track. Just about every body will tell you what they run.
Then gear a bit taller for a torquey motor or shorter for a speed motor. Ultimately, it is based on motor temp. Geared properly, your motor should be from "warm" to "hot", but not hot enough to burn. You should be able to hold your motor in your hand without discomfort. You should also be able to see on the track how you are doing on speed. Main straight is the easiest place to see, but also look at corner exit speed and punch.
If you don't want to ask, or can't, I'd start with a rollout of about 1" to 1.2", or about 25 to 30 mm rollout.