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I currently am running full Shimano Sora.

The crankset is 34/50T. The cassette is 11-34T 9 speed.

If I upgrade all my components to Ultegra, this being the rear derailleur, cassette (11 speed) and the front derailleur. Will the Sora crankset still work with the Ultegra gears? I don't really want to spend $500 on a new Ultegra crank when the one I have now is fine.

I am purchasing the 11-34T Ultegra groupset.

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  • That is a jump of 2 speeds (thinner chain). The difference of one is usually fine, two might be somewhat less reliable.
    – Vladimir F Героям слава
    Commented Jan 3, 2020 at 10:20
  • I'm happily using a triple front crank from a 15 speed (5 speed rear originally) with a 9 speed rear cassette/chain/mech/shifter and it works perfectly. The only trick was to mash the front mech cage a little thinner to be closer to the chain, and only by a millimetre or two. Try what you got now, and if it doesn't work then stop and re-evaluate.
    – Criggie ♦
    Commented Jan 4, 2020 at 2:00

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Retaining the 9 speed crank will likely cause front shifting issues. 11 speed chains are narrower so chainrings have to be slightly closer together on 11 speed cranksets. Shimano's documentation does not list any compatibility between 9 and 11 speed components. The general rule often quoted on this site is that you can get away with a 1 speed difference but not 2.

Something else to consider is that you will be severely compromising the Ultegra group by keeping the Sora crank, so you are not really getting an upgrade for the money spent. You would be better off getting a full 105 groupset that you know will work properly and give you the full benefit of the higher level components.

BTW, you say you will upgrade the cassette and derailleurs, but don't mention the shifters. You will of course need Shimano 11 speed group shifters to work with the Ultegra derailleurs.

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    Multi speed chains from 9 to 12 speeds have inner width of 11/128″ (2.18 mm). (according to bike.bikegremlin.com/3555/bicycle-drive-chain-dimension-standards/ ) It's only the outer width that changes because of thinner plates and shorter rivets.
    – Carel
    Commented Jan 3, 2020 at 14:54
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    Narrower outer width is the one that allows chain to wedge between rings. You don't want it to happen.
    – ojs
    Commented Jan 3, 2020 at 16:01
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In short, yes but not well.

The distance between the chainrings in a Sora crankset is different than the Ultegra crankset. So if you have an Ultegra shifter and front mech, you may experience some issues (chain rub, delayed shifting etc).

So it will work, but not as well as it should.

An alternative is to get a 105 crankset, or other crankset of similar dimensions (like a Praxis Works for example). You could always set it all up with your Sora crankset and see how it goes. But be prepared to get another, more suitable crankset. Maybe post a different question that asks which cheaper cranksets will work with R8000.

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    So can I purchase a 105 Crankset? Will this still work with the Ultegra gears?
    – Nicholas
    Commented Jan 4, 2020 at 1:41
  • If you get an 11speed 105 crankset it will work for sure. Also if you think your question has been answered, you should consider accepting an answer.
    – abdnChap
    Commented Jan 4, 2020 at 8:45
  • @Nicholas The last 10 speed, 105 groupset model number is 5700. So for the crankset, FC-5700 or 5750 (compact double) or 5703 (triple) are viable model numbers to consider. There are many new and used options on the market for this generation. The 11 speed 105 groupset carries model number 7000, the cranksets having the prefix, FC-. Either of these would tend to be a better option in many ways to keeping the Sora. An additional suggestion would be to look at slightly older Ultegra cranksets with model numbers 6700 and above.
    – Jeff
    Commented Jan 5, 2020 at 7:17
  • I would try and get an 11 speed crankset and try not to get a 10s one. Also, 105 (5800) is also 11s as well as the 7000 one.
    – abdnChap
    Commented Jan 6, 2020 at 8:50

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