No problem. It's nice to have a range of pinions to try. Say like 18-21 for starters. Gearing all depends on what motor you have. To high a # and you can overheat your motor which can burn up your comm and your brushes.
if your racing then dont go that high that motor will be toast asap. a guy i raced with always ran 17/87 with a p2k. that motor really isnt a truck motor. too rpm-ish. get a p2k or p2k2 for it and you will be happy