I am running a 14-20, 17-17 and am really happy with it. I may try to gear up even higher than that and see how I like it because I would like to have a higher top speed. I will have to see if it's possible to run a 15 tooth on the counter shaft and still be able to take up the slack in the chain with the tensioner. Gearing has a lot to do with what type of terrain and riding you are doing too.