Ultegra and 105 compatibility

Wondering if somebody could shed some light - I need to replace a left crank arm due to damage. My chainset is 105 5800 170mm and looking through ebay there are a few ultegra 6800 170mm left hand cranks available.

Will these fit?

Thanks in advance

Perfect fit, no issues at all.


Yes, they’ll work fine as both are (afaik) 11-speed setups from the same generation. Mixing different generations can be more complicated and Shimano doesn’t support mixing 10 and 11-speed setups although anecdotally even a 5700 transmission and an ultegra 6800 crankset work fine.

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Thanks for the advice, much appreciated!

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Every generation of HollowTech crank arms are cross-compatible as the splines haven’t changed, to the best of my knowledge. The left arm isn’t exactly what you’d describe as ‘speed specific’.



My bad. I read this too quickly. I thought he was going to take this opportunity to upgrade the crankset. :slight_smile: Detention for me!

I do that all the time.


No problem at all.

Re-cycling this thread:
My big Chain ring is worn and needs to be replaced. It’s a 105 5800 chainring and crank arm. Would an Ultegra chainring fit?

6800 would. Not R8000, as it is a 4 bolt pattern versus the 5 bolts of 5800/6800.


5800/ 6800 are 4 bolt as well, but won’t fit bc the inner chainring on r8000 series moved inboard ever so slightly.


But 105 5800 is compatible with Ultegra 6800, right?

Yes. And I’ve done exactly this, fitted an 6800 large chainring to a 5800 crankset.

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