Originally Posted by natskiboy
Im going to use a stock motor on my 415. What size pinion should I use? I have the 102T spur
Depends on a couple of things.
What motor? (ROAR, Quad mag, Monster, p2k2 etc)
What size is the track? (mainly straight length)
Rule of thumb is you want the motor topping out roughly 2/3rds to 3/4rs down the length of the longest straight.
Best advice is go to a local track, and ask people there what they run.
Personally I always err a little on the cautious side to begin with, so if some suggests (for example) and FDR of 7.5, i'll go around 7.8 to start, then work my way up. (remember, the lower the FDR, the higher the top speed/lower the acceleration)