Originally Posted by dabern

Not trying to add to your confusion, but I live in Asheville NC and ride these mountains on my fixed...by "mountains" I mean the 6-9% grades, not the 15-20% ones. Right now I'm on a 45x20 and it's about right for here as long as I don't try the really steep stuff...I don't know where in the BR you live, though. Generally speaking, 3 teeth on a chainring is about equal to 1 tooth on a cog...42x18 that you're talking about would be roughly equivalent to a 48x20 but with the 48x20 you'd really have no lower to go so I'd say get the 42 tooth CR and then see how it goes...if you need lower then try a 19 or 20 cog with the 42...your results may vary, of course. Anyway, good luck!