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I'm thinking of upgrading my bike, which has a Sora 9-speed system on it (50/34 chainset). The upgrade is for esthetic reasons - i simply like the look of the internal cable routing. That being said, it is not an absolutely essential upgrade, and if it costs too much I will not do it.

My plan is to buy the new Shimano 105 5800 11-speed cassette, shifters and chain. I understand that the 11-speed chain is thinner than a 9-speed. Does this mean that I also have to buy a new crankset to replace my 50/34 Shimano Compact FC-R345 Octalink?

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    I imagine he means internal as in cables go under the bar tape rather than at right angles on the sora.
    – Holloway
    May 12, 2015 at 21:29
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    I have been running with a 10 speed cassette with 8 speed chain-rings for a couple of years now. I use a 10 speed chain.I would not expect that you will have problems with 11 cassette, 11 chain and 9 chain-rings. The chain walls get thinner so you may find that the chain gets stuck between your chain-rings. This has happened to me only once, but I did have to release the screws holding the chain-ring onto the crank to free it up.
    – DanS
    May 13, 2015 at 12:18
  • Yes, the shift cables routed under the bar tape. I'll try the shifter/cassette/chain combo in a couple of months. I have a 300 km ride coming up in a month, and I'm not taking any chances there.
    – B Larsson
    May 13, 2015 at 20:27

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Shimano publishes a compatibility document.

Go to URL http://productinfo.shimano.com/#/ , select "compatibility" to download a document "2015-2016_Compatibility_v010_en.pdf"

According to that document, you would also need to change you crankset, your front and rear derailleurs, and possibly your bottom bracket.

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  • Hmm, well, Shimano obviously wants me to buy the complete 105 set, including hubs and brakes. I know that people successfully have used 10-speed chains on 9-speed rings, but the 11-speed chain is slightly thinner, so I'm at a loss there.
    – B Larsson
    May 13, 2015 at 20:32
  • If you want to save money you might consider going Tiagra 10 speed components, except for the shifters which would be 105 to give you the concealed cable routing you want (beware it puts more stress on the cables and could shorten cable life). The chart shows that setup would be compatible.
    – Craig Hicks
    May 13, 2015 at 21:13
  • Incidentally, now that 105 is using 11 speed, you could probably pick up used 105 10 speed shifters (FS5600?) on ebay.
    – Craig Hicks
    May 13, 2015 at 21:23
  • @CraigHicks Perhaps there's been a new generation of Tiagra since you wrote your answer; my bike (bought in November/December 2017) has Tiagra 10-speed levers and they have the concealed cable routing.
    – David Richerby
    Apr 3, 2019 at 17:24
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You should just be able to replace the chainrings for 11 spd ones.

You can also get 9-spd 105 shifters if you just want tidier cable routing (I assume you mean internal as in under the bar tape) which would let you keep the rest of your groupset as is.

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  • haha, I love the use of the word "just" - maybe you should mention how much this would cost?
    – PeteH
    May 12, 2015 at 20:07
  • @PeteH, I imagine it'd be cheaper than replacing the whole crankset. The whole thing is not a cheap endeavour though, granted.
    – Holloway
    May 12, 2015 at 20:09
  • ...but not quite as cheap as using a 9sp chain ;-)
    – PeteH
    May 12, 2015 at 20:19
  • @PeteH How is just using a 9 sp chain going to achieve tidier cable routing?
    – paparazzo
    May 12, 2015 at 21:20
  • @Blam how is a new chainring for that matter?
    – PeteH
    May 12, 2015 at 21:22

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