The largest width tire that will fit on any bike is pretty much a crap shoot. I'm all about trial and error. Oversized tires can rub in all kinds of places that you might not have considered. Some that I've encountered have been the front derailleur when the chain is in the granny ring, the chain when the chain is on the largest rear cog, front tire rubbing the bottom of the fork crown. I've read a lot of posts by people worrying about an extra wide tire fitting such and such of a rim. I've never personally encountered a problem with the rim other than bead seat diameter issues.
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