Hi all - my first post I'm fascinated with the idea of touring and I am looking into buying a trek 520 for a fully loaded tour with a buddy from Pittsburgh to DC. Never really been into biking before... but touring looks like it could be quite an experience. I've been reading the posts about switching out the crank and/or lowering the gearing on the trek 520 and I've found a wealth of information - thank you. I was wondering, however, has anyone tried to add a 4th cog with the Mountain Tamer Quad? Someone had mentioned that they did so with their tandem, but I didn't see anything about the trek 520. Anyway, I tried reading what the manufacturer of the Mountain Tamer Quad (Abundant Adventures) had to say regarding if the product would be compatible with a bike or not, but I really wasn't able to figure it out. (Like I said, I'm new to bikes and not really familiar with all the different variety of parts and stuff yet - sorry). Thank you in advance.