Road bikes are typically 165 to 175mm. With 170 on most of them. MTBs are typically 175-180, with 175 on most. There are plenty of exceptions, of course, but I hardly ever see them.
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Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
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SB forever