Hi Adam,

How hilly is it where you live and what kind of riding do you do?

20t is pretty big in the back for just regular road riding/pub cruising/etc. Assuming regular gearing rules you'd want something around 70 g.i.


With a 20t in the back you get the following for common front chain ring sizes.
46 48 50 52
62.1 64.8 67.5 70.2

I'd probably just forget the 20t and go ahead and get a 17t/18t since 50/52 starts giving you clearance issues with a lot of frames. 46/48 paired with a 17/18 gives you better options and will fit with no issues on a larger amount of frames.