Medium Cage Ultegra RD?
05-22-14, 10:56 PM
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Medium Cage Ultegra RD?
Specialized Tarmac, 53x39 chain ring. About a year ago, I replaced my original rear cassette - an 11x25 or thereabouts - with a wider-span, 12x30 cassette. The OEM short cage Ultegra RD worked okay with the new rear sprocket, but I now seem to be going through chains a bit faster.
So i've ordered a medium-cage Ultegra 6700 RD, hoping it's a better match. At $89, I hope I've made the right decision. Any feedback appreciated. DB
So i've ordered a medium-cage Ultegra 6700 RD, hoping it's a better match. At $89, I hope I've made the right decision. Any feedback appreciated. DB
05-23-14, 08:29 AM
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I can't see how the rear derailleur's cage length could possibly have any effect on chain wear. The problem isn't there and a longer cage rd won't make any difference.
05-23-14, 08:40 AM
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The only possibility that comes to mind is that the RD chain wrap has been exceeded, and the chain is rubbing against itself when in a small/small combination because of the derailleur trying to wrap more than it can handle... but then the best solution would be to avoid cross chaining.
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05-23-14, 08:50 AM
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I'm thinking Triple Road RD , are not as long an arm as Mountain triples and thus can be considered Medium ..
to confirm ... measure. ..cage length is about wrap up... [Tooth count] ( Big+big)-(small Small )= wrap capacity
to confirm ... measure. ..cage length is about wrap up... [Tooth count] ( Big+big)-(small Small )= wrap capacity
Last edited by fietsbob; 05-23-14 at 08:53 AM.
05-23-14, 08:14 PM
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Well, maybe I've just been riding more. :-) In any case, a 53/39 chain ring coupled with a 12/30 cassette SEEMS like a lot for a short-cage derailleur to handle, whether or not accelerated chain wear is one of the results. I'll put the new derailleur on next week. I'll be careful to install the new chain using the "small-small" method (which requires threading the chain through the RD), and will let you know how it all works. Cheers. DB
05-23-14, 08:31 PM
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Shimano's Tech Doc web site has the installation instructions and wrap capacity for the past few Ultegra derailleur models. For the FD-6500 (9-speed) and FD-6600(early 10-speed) models the SS short cage models have a wrap capacity of 29T and the FD-6700 (later 10-speed) SS has a wrap capacity of 33T. The long cage GS versions can wrap 37T and 39T respectively
Your 53/39 + 12x30 cassette needs 32T of wrap if all possible combinations are to be used. So, if you size the chain for big-big, as you have to do for safety, your older SS model will require you to give up the two small-small combinations which are no sacrifice. The FD-6700 SS has adequate wrap capacity.
If you replace it with a GS, you can safely size for small-small since there is enough wrap to still allow big-big.
All of the above is for info only. There is no effect on chain life in either case.
Your 53/39 + 12x30 cassette needs 32T of wrap if all possible combinations are to be used. So, if you size the chain for big-big, as you have to do for safety, your older SS model will require you to give up the two small-small combinations which are no sacrifice. The FD-6700 SS has adequate wrap capacity.
If you replace it with a GS, you can safely size for small-small since there is enough wrap to still allow big-big.
All of the above is for info only. There is no effect on chain life in either case.
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