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Old 08-18-11, 08:00 AM   #1
dabac
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Front derailer: pros and cons of seat tube mount vs BB mount?

Hi all,
Well, the headline says it all really. Am looking to buy a new (MTB front) derailer, and suddenly realized there was another option I hadn't considered. Never used a BB mount before.

The BB mount seems somewhat neater, but I imagine alignment might be trickier.
Seat tube mount is an old aquaintance; I'm not worried about any surprises there. It's certainly worked well enough before.

Any preferences, tips and pointers, let me know.

Cheers,
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Old 08-18-11, 08:37 AM   #2
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BB mounted FDs are typically used where seat tube mounting is not an option (such as on 'bents). Not sure why you'd use one if seat tube is an option.
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Old 08-18-11, 08:49 AM   #3
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Not sure why you'd use one if seat tube is an option.
Neither am I. But having the option open increases the number of possible candidates when bargain hunting...
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Old 08-18-11, 09:05 AM   #4
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Bottom bracket mounts are usually limited to suspension MTBs and other bikes where the seat tube is not round and has no braze-on mounting tab. Also, check to be sure the bb mounted derailleur has the cable pull from the correct direction as many MTB's use a top pull arrangement and that's unusual on road bikes.

Me? If a seat tube clamp-on or a braze-on adapter fits, that's what I'd use.
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Old 08-18-11, 09:19 AM   #5
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Then you have to consider the Big ring size you want to run.

2 schemes decide that for you.. BB mount ,
and where a braze on mount is fitted on the seat tube.
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Old 08-18-11, 09:54 AM   #6
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Then you have to consider the Big ring size you want to run.
Good point. BB mounts usually assume a MTB crank and a 42 or 44T big ring and you can't adjust the derailleur high enough for a typical road 52 or 53T chainring
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