if the track has turns where you need to be out of the gas more often, use the smaller driver, if it has wide turns and you dont have to lift, use the biggest driver you can get away with using. Im usually on a driver that is one tooth bigger or one tooth smaller than what everyone else at the track is on, rarely am i on the same gearing as everyone else. I just like to try new things, and by doing that i found what works best for me at certain tracks, and what line i need to be running at those tracks. It takes time to really figure out the right gearing for a track. With that said, i am usually on a 14 thru 16 driver for the tracks i race at, one is a 1/5 mile oval with sort of wide turns and banking, the other is a flat track and also around 1/5 mile but with tight turns and long straits. For the track that is banked with wider turns, im usually on the 16, and for the one with tighter turns, im on a 14 or 15. i keep my rear gear between 59-68 and adjust the front according to how tight the turns are and how quick i wanna get off the corners. People have said it looks like im cheating because i can pull good speed off the turns and carry that speed down the straits, its all in the gearing you choose and how good your kart is set up. A kart that is set up poorly and not getting thru the corners good would need more gearing to keep the speed and momentum going, while a kart that is properly set up and has the right tires will make alot more speed and wont need as much gear. I have ran as low as 15-58 on the 1/5 mile banked track in box stock class, turning about 6000 rpm along with 11.8-12 sec laps on a good night.