gearing
 

I have a bk2 and i am running the smaller spur gear by losi what pinion should i use thanks.

Stock, Mod, Brushed, or BL?

yea what motor are you running

oops that sliped my mind a moster 27 on a open track

19tooth

with a stock motor i always ran a 20 tooth with either the 78 or 81

I ran a 21 w/ a Monster in my BK2 but I did have the 82 spur also.

You can go higher for racing, to around the 23-24 tooth range..... If you carry decent corner speed, don't run into stuff much, and take care of your motors, cut comms and new brushes, and don't run long practice runs that really heat up the motor. 21 or so is probably good for starting out IMO.