pista's are 3/32 stock. i upgraded my drivetrain and got 1/8 whick just feels better to me. If you change your cog, you will most likely need to change your chain as well (as they generally wear together) though with an 09 you might get away with only changing the cog. Just buy a rocket ring from harris cyclery as they are only 18 bucks and that way if you hate it you wont have put too much money in.