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I am currently upgrading my bike from a 9 speed to an 11 speed system. I am currently using shimano 105 components and will continue to use them within the new system. Current bike has a shimano 105 rear derailleur but does not specify if it is unique to a 9 speed system. Will I need to buy a new rear derailleur?

  • I can't find anything definitive, but I'm pretty sure the cable pull is different between Shimano 9spd and 11spd. – Fred the Magic Wonder Dog Mar 11 '15 at 15:11
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    From Shimano 9- to Shimano 11-, Shimano recommend you need a new everything. You might get away with the brakes, but certainly as regards drivetrain you should be prepared to change the lot. Also your freewheel hub, most likely, since this has also changed for 11-speed systems. The thinking is simple - an 11-speed chain is that much narrower than a 9-speed chain, therefore all components that the chain touches (incl rear derailleur) are affected. – PeteH Mar 11 '15 at 19:10
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    Worth also pointing out that there is a school of thought that says these differences are sufficiently tiny that it is all a marketing ploy by the bike companies, to get you to replace your kit. At this point, you pay your money and take your choice...seriously, it boils down to how much a person feels like spending money – PeteH Mar 11 '15 at 19:18
  • I already bought new wheels whose hub is 11 speed compatible. I obviously will be getting a new cassette with a new chain along with new shifters to index correctly. I plan on leaving the brakes as are. With this input I'll probably just go ahead and upgrade my rear derailleur as well. This will also allow me to put a full drive train on a spare frame. Thank you for the assistance. – Danny P Mar 12 '15 at 12:40
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    @FredtheMagicWonderDog Pull ratios can be found online. The Maintenance and Repair chapter of the Bicycles Wikibook is one such source. – Rider_X Feb 4 '16 at 19:45
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This page has the best answer I've found so far

http://blog.artscyclery.com/science-behind-the-magic/science-behind-the-magic-drivetrain-compatibility/

Reading between the lines, the cable pulls from 9spd to 11spd are probably close enough, but the derailleur ratios are significantly different. 1.4 vs 1.7. This means that the 11 spd indexing in your new shifters will not work correctly with your old derailleur.

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You'll need to change the chainwheels and the cranks, the rear derailleur, the brake-shift levers, the cassette and the chain of course. The rear wheel probably has an older hub but then if you're lucky and the hub is designed for 10-speed as well it will also take 11. The brakes won't need changing but then the newer ones are designed for less friction in moving parts. Technology trickle-down from Ultegra.

  • All my older Shimano wheels are 10-speed - But NOT 11-Speed compatible. So a 10-Speed hub is not necessarily going to work with 11-Speed. – OraNob Feb 4 '16 at 15:42
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    Shimano moved to Super SLR pull ratios on their brakes recently so the older brakes will no longer be optimal (see bicycles.stackexchange.com/questions/20295/…) – Rider_X Feb 4 '16 at 19:40
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There are numerous top end bike companies selling their bikes with part 105 11sp builds . You need obviously the 5800 shifters, front/rear mech and chain. But you typically see money being saved by using non 105 brakes and chainset.

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    This doesn't answer the question. Can you edit in specifics about whether the 9 speed 105 derailleur will work with an 11 speed shifter and cassette please. – Móż Feb 4 '16 at 22:23
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To specifically answer your question, you will have to change the rear mech (derailleur). If for nothing other than 11sp chain will not fit onto the jockey wheels correctly. You could change the jockey wheels, but they are thinner on 11sp vs 9sp.

To take this a step further, you will need to replace all of the groupset components, including the brakes as 5800 has a slightly different action/cable pull. Having tried this before with customers bikes, it causes major issues and very poor brake performance (not somewhere you want poor performance).

On a positive note, 5800 brakes are leaps and bounds better than their predecessors!

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You won't need to replace your rear derailleur. Cable pull is determined by the shifters so if you're getting new 11 speed shifters you can use ANY rear mech as long as it has a long enough cage to accommodate the largest rear sprocket. For example i'm pretty sure that if you have a short cage rear mech you won't be able to run an 11-32 cassette. The rear mech has an infinite range of movement between the high and low stop screws so as long as they are adjusted properly you'll be fine. B-tension screw is what brings the cage in or out to accommodate the largest cog.

The reason for any problems in compatibility is that for 11 speed there are more cogs (11) packed into the space between the hub flange and the frame dropout so the spacing between cogs is narrower which means the chains need to be narrower and the shifters pull less cable with each click. But if you try and run a 9 speed chain and chainset the teeth are wider so the chain won't sit properly on the chainrings.

So in short you'll need a new chain and cassette and shifters but you can keep your front and rear mechs.

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    11-speed Shimano derailleurs have different actuation ration than older ones. – ojs Feb 7 '17 at 18:33
  • Welcome to Bicycles @tim. Thanks for answering one of our questions. Since you say the opposite to other answers, it would help if you explained how you know this. And we recommend that new members take the tour to make best use of the site. – andy256 Feb 7 '17 at 20:20

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