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new derailleur when moving from 9 to 10-speed cassette?

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new derailleur when moving from 9 to 10-speed cassette?

Old 02-27-09, 10:22 AM
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new derailleur when moving from 9 to 10-speed cassette?

I busted my tiagra sti shifters and found some ultegras at Nashbar for only $149 so am making the switch on my commuter from 9 to 10-speed. (If someone wants the right hand, rear shift/brake lever, make an offer--or the busted front/left for that matter).

I have the new cassette and chain, but yesterday I was chatting with the mechanic at the lbs and we started talking about how, even though the distance from the biggest to the smallest cog would be basically unchanged, he didn't think the derailleur (a tiagra 9-speed) would work, and that I would have to buy a 10-speed derailleur.

Anyone have experience with this? I did a quick search of the forum, but couldn't find anything, probably because I couldn't figure out the right search term. Any thoughts would be greatly appreciated.
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Old 02-27-09, 10:29 AM
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I think it should work, but the shifting may not be a as crisp and fast. The reason being the RD cage spacing is not as narrow as the 10spd RD. A 9sd Shimano RD is wide enough to run a 8 spd chain.
Give it a try before buying a new 10spd RD.
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Old 02-27-09, 10:47 AM
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narrow pulleys

Thanks for the response. Do you think I could replace the pulleys in the cage to narrow it and get the "crispness" that might be lost? This is a commuter, around-town, light touring bike, so super crisp isn't a huge concern, but sure don't want sloppy.
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Old 02-27-09, 11:22 AM
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I think it work just fine. Changing the jockey and chain guide should improve it's function with a 10 speed chain ----- give it a try and let us know how it worked. Lp
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Old 02-27-09, 11:24 AM
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Thanks again. Considering the cost of a new derailleur, it seems the low cost way to try before plunking down the bigger bucks.
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Old 02-27-09, 11:33 AM
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I recently made the switch, and my tiagra rd worked just fine. The shifts did seem crisper, however, the shifts were more crisp once I got my new rd. Could have just been the difference in the tuning, not sure.
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Old 02-27-09, 12:33 PM
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Originally Posted by bleckb
Thanks for the response. Do you think I could replace the pulleys in the cage to narrow it and get the "crispness" that might be lost?
No. Internally (i.e. the way the teeth see the chain) a 10-speed chain is identical to a 9-speed. Any difference would be with the guides that contact the outside of the chain. This is much more important with the FD than with the RD since it's the FD cage itself that moves the chain. In a RD the cage essentially serves only to support the jockey wheels.

IMO the 9-spd RD will work just fine.
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Old 02-27-09, 01:23 PM
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These are all the sorts of answers I could hope for. Once I finish putting it together (makes me want to skip out of work and do it all now; like I'm getting any work done today anyway) I'll report back.

Was there an earlier thread on this I just didn't find? It doesn't seem like it would be a new kinda question. If there is an earlier thread, I'd like to look at it if anyone could point me to it. No need to search it out, but if you know off the top of your head, I'd appreciate seeing what came before.
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Old 02-27-09, 08:36 PM
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Ooh, perfect timing. I just toasted my RSX 8-speed brifter and will need to replace it. If I replace it with a 9-speed Tiagra or 105 brifter and use a 9-speed cassette can I continue to use my 8-speed 105 derailer or will it have to be replaced?
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