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Old 10-26-06, 04:42 PM   #1
infernobutterfl
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what is the difference between a mountain and road derailers?

As topic states: What is the mechanical difference between a mountain bike derailer and a road bike derailers?
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Old 10-26-06, 04:57 PM   #2
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mechanical difference is cage length.
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Old 10-26-06, 05:01 PM   #3
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No meaningful difference, except that mtb deraillers tend to wrap more chain (b/c mtb's usually have a wider range of gears) and so they have a longer cage. But road bikes with triples have to wrap more chain, and touring bikes usually have really wide gearing range like mtb's, and so those road bikes use medium- or long-cage rear ders.

Also, mtb rear ders can handle a larger max cog than road, even long-cage road.
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Old 10-26-06, 05:24 PM   #4
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There are bigger differences in the front derailleurs, cable pull, throw ratios, and cage arcs.
The mountain bike rear derailleur has a longer upper parallelogram to handle larger cogs, generally rated up to a 34t, as well as a longer cage to handle more chain wrap.

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Old 10-26-06, 06:50 PM   #5
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Also, cheap MTB's (although I haven't done research) have larger derailleur pulleys, which I guess would serve primarily to wrap more chain. Secondly these seem to be a bit quieter, but that's with limited experience.
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Old 10-26-06, 07:42 PM   #6
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Does wrapping more chain on the rear der. equate with slower shifting? The '96(?) Shimano Altius rear der on my Trek 850 (7 speed) shifts noticeably faster than the 105 rear der on my 9 speed road bike. Maybe this has to do with the smaller chainrings on my MTB?
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Old 10-26-06, 07:52 PM   #7
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Could be any number of things causing the difference in shift speed kmart... I have found in my experience that B-tension plays a pretty big factor in shift responsiveness however.
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Old 10-27-06, 01:08 PM   #8
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Quote:
Originally Posted by kmart
Does wrapping more chain on the rear der. equate with slower shifting? The '96(?) Shimano Altius rear der on my Trek 850 (7 speed) shifts noticeably faster than the 105 rear der on my 9 speed road bike. Maybe this has to do with the smaller chainrings on my MTB?
Probably has more to do with the condition of the shift cables, cable housings, and how clean the shifters are.

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