I would say the best thing to do would be to pick up a couple different sizes. I carry with me 15-19 tooth pinions. One track I go to the 17 works best while another track likes the 19 and honestly i could probably go up to a 20 or 21 to be most ideal.

I am currently running a 2250 tekin motor on 3S batteries. I will be switching over to 4S batteries shortly and I assume I am going to have to drop down a few teeth for each track once I do.

Pinions are pretty cheap and every track is different. Just keep a close eye on your motor temps, run times, and how it seems to work out to your liking on the track and adjust accordingly.