Oh, no! Do I need a new rear derailleur???
06-12-09, 02:33 PM
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Oh, no! Do I need a new rear derailleur???
I have a Specialized Tarmac Comp triple with 105 components. Recently, I ordered a pair of light weight wheels for racing and special occasions. I also ordered a Dura Ace CS-7900 Cassette (same gearing to my 105 cassette: 12-27) to go with the light wheels. I will replace my old chain with a new Dura Ace 7900 chain. Reading this CompetitiveCyclist page, I wonder if I need a new rear derailleur. Can anyone please advice? Will my 105 rear derailleur work with my new Dura Ace cassette?
I thought it's as simple as switching wheels only. No?
I thought it's as simple as switching wheels only. No?
06-12-09, 02:37 PM
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You will be fine. Didn't read the link but I assume it is a reference to cage length in regards to the 27 cog. You can shift a 27 with either a short or long cage rd.
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06-12-09, 04:04 PM
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Ah. Read the link. They are talking about the chain wrap. 7800 series as well as 6600 and 5600 series (ultegra and 105) where designed to use cage length length to address chain wrap. In actuality you can run a compact with a 12-27 with a short cage previous 10 spd rd.
They are saying that they changed the 7900 rd to have more wrap. Yay. Doesn't matter for a 12-27 because the old rd still had enough wrap to handle it.
The only concern would be running an 11-27 or 11-28 with an old derail. Both of these cassettes have a larger span and require more wrap. In practice thought I bet you would find that the old style would still work just fine. Especially if you were run ing a full size crank.
They are saying that they changed the 7900 rd to have more wrap. Yay. Doesn't matter for a 12-27 because the old rd still had enough wrap to handle it.
The only concern would be running an 11-27 or 11-28 with an old derail. Both of these cassettes have a larger span and require more wrap. In practice thought I bet you would find that the old style would still work just fine. Especially if you were run ing a full size crank.
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06-12-09, 06:12 PM
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Hey, thanks all for the reassurance. Going broke with all the upgrades already. Now, bikeybikebike is just messing with me, right? 
