I have a Trek 6500. I need to replace the chainring. Where can I get compatibility info? Do you have any opinions of LX versus Vuelta SE? And can I use the old Bontrager crank that came with the bike with a new chainring? I have no idea what I'm doing, but I'm learning and I have to increase my learning curve exponentially before I do this. I have had a few bad experiences with LBS's so I want to know the facts before I go back into the trenches.