Guys, this may pee some of you off so look away if you dont want that.

I just wanted to know what a 30 rollout or 42 rollout is, as in how do you work it out to get the 30, 42 or be whatever number it is, previuslly when i started racing electrics i jst used one spur one pinion and that was it. and had the same stock motor for 8months without a cut(still went hard--till it seized).
So any helo is appreciated. thanks