Cmotif, it is really hard to say. I can't give you any recommendations because I have no idea what the standard spur gear sizes are. Also, gearing can vary as much as 2 teeth between motors of the same model. I think the rule I hear most often is to gear so that your car peaks out 3/4 of the way down the straight. Maybe you could pool all of the pinions your club has and test them on one car, find which one works best with a specific motor and go from there.