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I'm planning to upgrade from 9 to 11 speed, Sora 3500 to 105 5800.

I'd like to keep my existing mechanical disc brakes, which I believe I can, but please correct me if wrong.

Also, if I bought the full 105 groupset with rim brakes (cheaper than set with hydraulics) and just sold the brakes, would everything else still work on my bike with disc brakes?

Lastly, other than brakes, what can I get away with not replacing. Bottom bracket, shifters, crankset, FD? Thanks.

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    Are you sure your hub (freewheel) is 11 speed compatible, a few are, most are not.
    – mattnz
    Jun 9, 2016 at 7:00
  • If your crankset is a double, then I think there's no reason for it not to work with 5800. FDs are incompatible, though, but you might just keep the Sora front shifter.
    – Klaster_1 Нет войне
    Jun 9, 2016 at 7:56
  • If you got the hydraulic set, you'd need the hydraulic brakes routed on your bike.
    – Batman
    Jun 9, 2016 at 13:44
  • You'll have to consider that when buying items separately the price for this upgrade will be likely much higher than buying a readily equipped bike.
    – Carel
    Jun 9, 2016 at 16:02
  • Do you have brifters or are the brakes and shifters separate ? I'm assuming this is a road bike with drop bars.
    – Criggie ♦
    Jun 10, 2016 at 1:26

2 Answers 2

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You'll need:

  • A Shimano 10 speed mountain/ 11 speed road rear derailleur

  • A Shimano 11 speed road front derailleur (since they apparently work differently than normal ones)

  • Shimano 105 shifters (Front and rear; given the cost of a new FD and the resale plan, you don't really want to reuse the old one + the old front shifter)

  • 11 speed chain

  • A freehub on your rear wheel which can take a 11 speed cassette

  • A 11 speed cassette

The brakes will work fine. If you do replace the crankset, you'll likely need to replace the bottom bracket as well. The crankset should work, but it might not be optimal -- on SRAM, the chainrings have been spaced slightly wider apart on 11 speed and the chainrings are likely a bit thinner than 9 speed, which may be the case with Shimano as well.

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  • Thx, yeah, as mentioned above, I'll buy the full groupset and replace everything except brakes. Might as well do it right. Yes, Shimano chainring spacing is different in my case.
    – pseudoware
    Jun 10, 2016 at 14:36
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Batman has the correct answer, but I'd like to mention a "cheat" for those who don't want to (or can't) upgrade to an 11-speed freehub.

I just went through the 9-to-11 conversion process with a 9/10-speed freehub. An 11-speed cassette wouldn't fit, so, using a Shimano 105 11-speed cassette, I removed the third-smallest cog (you'll see why when you do this -- it has to do with the way the cogs mesh together) and added a 1mm spacer behind the 34t cog to add back enough width to get the lockring to bite. Now I have a cassette with 11-speed cog spacing but only 10 cogs. I set the limit screws on my rear derailleur and my 11-speed shifters shift the whole range perfectly, except the last click past the smallest cog doesn't go anywhere.

As for chainrings -- although an 11-speed chain is narrower than 9/10 on the outside, it's the same width on the inside, so any chainrings should work with an 11-speed chain.

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  • Or he can go with a new 11-34 8000 cassette which fits to MTB/old road freehub bodies. Not sure if any available 5800 cage length would work, though.
    – Klaster_1 Нет войне
    Jun 10, 2017 at 16:07

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