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Currently running a full 105 r7000 group on my bike. I would like to swap my existing 172.5mm 105 r7000 crankarms for 165mm ones. They seem to be very hard to come by, especially the right one, so I started looking for a crankset. I have found a good offer for a 105 r7100 crankset and would like to know if I could simply "upgrade" to the 7100 crankset. The Shimano compatibility table doesn't list the r7100 front cassette as compatible, but I can't really wrap my head around why that would be. Are the chainrings further apart (or closer together), making shifting impossible (or sloppy)?

I appreciate any answers. Greetings from Germany

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An R7100 crankset mixed with 11-speed R7000 components will probably work just fine.

Maybe even almost certainly.

I've mixed 10- and 11-speed cranksets with no problems - other than the 10-speed FSA one shifts even worse with an 11-speed chain, if that's possible to believe. My Shimano cranksets don't seem to care if the chain is 10- or 11-speed. I strongly suspect that the difference between 11- and 12-speed is similar.

Shimano's compatibility charts tend to be really conservative - if Shimano's charts say something is compatible, it will work in that combination. The fact that a certain combination is not on the charts is does not even come close to ruling out components working together just fine. (Just pay attention to things like cable pull ratios when mixing shifters with derailleurs - THAT does matter) IIRC an 11-speed chain is 5.4 mm wide, while a 12-speed chain is 5.25 mm wide - on the outside. (The inside width is the same). The R7100 crankset is designed for that narrower chain. But it's only a difference of 0.15 mm.

Your bike's exact configuration could have some effect. Things like your exact chainline and chainstay length, and even how much tension your rear derailleur puts on the chain could affect the shifting. And the width of your derailleur cage. Maybe. And maybe only on Tuesdays when the moon is full.

You might have a greater chance of dropping your chain - so perhaps add a chain catcher so it won't drop to the inside and potentially chew up your frame. That's probably your worse-case scenario.

But chances are you won't notice one bit of difference.

Bottom line, though, is the only way to know for sure is to try it.

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    Shimano specs afair also say there is 1mm chainline difference between 11- and 12-speed, but, as you said, that's probably nothing that can't be sorted out by FD adjustments, in worst case, your shifts are only 95 percent crisp, but that's probably acceptable in mostcases. During the pandemic, pro teams were mixing and matching 11/12-speed components due to production shortages, afaik mostly 11-speed cranks with 12-speed drivetrains but except allegedly more frequent chain drops (in race conditions), it obviously was considered "rideable".
    – DoNuT
    Aug 22, 2023 at 5:57

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