What size pinion for brushless stock engine.

Hey guys I need some help trying to determine what size pinion I should use for my micro rs4. The brushless engine is going to be in the 2200s kv, have to wait and see exactly when it comes in from my local hobby shop. I trying to figure out what size pinion I should be using with that setup. Also I will be running a 2s lipo pack 850mah 25c+ 7.4v.

[alfred]

If you plan on going for speed then go with a 13th pinion.......gear down if you need to.