I use 24 (soon to be 29 custom made! bling bling!) tooth pinions with 51 tooth spur. On my very, small (unextended), almost stock truck, my 18 cell and feigao 8xl just flys. 24-51 just is too much acceleration, can't controll it. I mean i could just dumb down the transmitter, but who wants to do that? Thats why i'm getting a FAT pinion gear!