There seem to be a lot of gearing questions lately... and unless 2 people run at the same track, its hard to be specific. Back in the day, the motor pinion on brushed motors could usually start at a certain number of teeth "over" the motor turns. So for example, if you were running a 13 turn motor, and were gearing "8 over" for that car, you could start with a 21t pinion.

Any thoughts on how this would apply to a brushless motor in a b4.1? It seems like its not quite as simple of a calculation, but I my best guess was (1.5*turns)+5 would be a good starting point without boost. That's a 31 on a 17.5, 25 on a 13.5, 21 on a 10.5... Any thoughts?