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Old 09-23-06, 02:26 PM   #1
BobL
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Road/MTB Bottom Bracket Compatibility?

Hi, Gang,


I have to admit I haven't posted here in a long time. I read and lurk, but haven't had much to say.

Anyway, I have one-of-a-kind bike. It started out as a hybrid, but I took off the straight bar/gripshifters and put on a drop bar with 105 STI shifters. I had to swap the out the rear derailler (it was low normal, not high normal) to make it work, but I've been riding it for over a year now. I have road bars and shifters with an MTB drivetrain, which uses Shimano DeoreLX Hollow cranks and bottom bracket.

I'm considering putting a road group on it, replacing the MTB triple with a 105 triple or Ultegra triple. Is the DeoreLX's bottom bracket compatible with an Ultegra or 105 crankset? If I need to replace the BB, is the threading compatible with what I'd need for a road BB?



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Old 09-23-06, 02:39 PM   #2
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The threading will be the same (English) but the width (road bbs are 68 mm wide and newer MTB's are 73 mm wide) may differ depending on the vintage of your frame. Also Shimano made two different Octalink bb designs and the road and MTB versions aren't the same. You will probably have to change the bb along with the crank.
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Old 09-23-06, 03:00 PM   #3
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And check the spindle length as there might be a difference between MTB and road (there was on my Fuji, going in the opposite direction). The offset on the right of the spindle will determine if your chainline is good and if there is any interference between the chainrings and chainstay, plus the Q-factor on the cranks.
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Old 09-23-06, 05:30 PM   #4
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Quote:
Originally Posted by HillRider
The threading will be the same (English) but the width (road bbs are 68 mm wide and newer MTB's are 73 mm wide) may differ depending on the vintage of your frame. Also Shimano made two different Octalink bb designs and the road and MTB versions aren't the same. You will probably have to change the bb along with the crank.
Thanks - I'll go measure that. The frame is a year old - new enough so that it came with a "low normal" rear derailler. That might be a problem.


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