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My Tiagra 4500 9-speed rear dérailleur has so much play now that if I select the lowest gear, the cage hits the spokes. Obviously this is a bad thing and I want to replace it immediately. The trouble is, they're like hen's teeth. There are plenty of 10-speed dérailleurs out there, but before I order anything, I want to confirm that 10-speed is compatible with 9-speed.

I've found conflicting claims on the internet, related to pull ratios. Can anyone put my mind at rest and let me order a new 10-speed dérailleur? I'd rather not upgrade the entire drivetrain as I'll be buying a whole new bike later this year.

12 comments

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glynr36 [637 posts] 2 years ago
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Chain Reaction have Sora 9 speed for £18, if you're replacing the bike this year that should see you through.

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therevokid [948 posts] 2 years ago
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ran a 10 speed ss mech on my 9 speed tiagra sti's for ages without any problems

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adamthekiwi [110 posts] 2 years ago
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I tried to use a 10-speed shifter with a 9-speed derailleur (105 shifter and Deore rear derailleur on my touring bike) and the pull-ratios meant that it just would not work - the total amount of cable pulled was not enough to move the derailleur from top to bottom. The opposite will probably be true of trying apply a 9-speed shift to a 10-speed derailleur - the cable-pull per index stop will be larger than the derailleur is meant to handle.

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adamthekiwi [110 posts] 2 years ago
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Peowpeowpeowlasers [380 posts] 2 years ago
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This is the problem, see - 50% say one thing, 50% the other.

I wonder if Shimano produce a compatibility table.

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Peowpeowpeowlasers [380 posts] 2 years ago
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glynr36 wrote:

Chain Reaction have Sora 9 speed for £18, if you're replacing the bike this year that should see you through.

I'm not sure if I'll keep the bike or not (probably not) but this is a good suggestion, thanks.

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Peowpeowpeowlasers [380 posts] 2 years ago
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The CRC description for a 105 5701 rear mech says it'll work with 8, 9 and 10 speed systems, so I'm going to buy one of those. If it doesn't work then I can just return it.

Thanks all for the replies, I will post back with results.

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Chris James [388 posts] 2 years ago
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Are you sure it is play in the mech, rather than a bent gear hanger?

I have never known that much play is a rear mech, in fact I wouldn't have thought it possible unless it was literally falling to pieces.

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carytb [82 posts] 2 years ago
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You could try a Deore 9 speed mtb derailleur. I have got one on my Tiagra specked Croix de Fer

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archie gordon [7 posts] 2 years ago
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I have a 105 ten speed derailleur on one of my bikes with tiagra 9 speed shifters
just use the limit screws to stop it going to far. never had a problem with it

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The _Kaner [770 posts] 2 years ago
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ST4500 shifters are showing as being compatible with the following rear derailleurs:
RD-7800
RD-6600G
RD-6600
RD-5600
RD-5600L

E of the bay dot com showing RD-4500 at under £30 (free p+p)
http://www.ebay.co.uk/itm/Shimano-Tiagra-Rear-Derailleur-RD-4500-SS-9-Sp...

If that's any help....

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Peowpeowpeowlasers [380 posts] 2 years ago
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Just to let people know, I replaced the old, worn out Tiagra 4500 dérailleur with a 105 5701 10-speed. It shifts perfectly, there are no issues. It's totally compatible.

As an aside, shifting is now hugely improved. Mind you, the old dérailleur really is a floppy knackered old thing with play in every direction. I'll take the (almost new) jockey wheels out of it and retire it to the recycle bin.

Thanks for all the help.