So my road bike has 105 di2 which limits cassettes to 34T with the longer cage mech. Would there be any compatibility issues with an Ultegra rear mech to run 30T and 28T cassettes? That is, keep the 105 di2 shifters and the rest of the system, just get the shorter cage mech from the Ultegra di2 gro…

^This. I wanted the faster front shifting and the hidden buttons to change screens on my Garmin, so I got UDi2 shifters and FD. AFAILK the Rd is virtually identical, and we weighed the chainsets in the shop; there is less than 30g difference. So both of those are 105. The Ultegra cassette has hyp…

Yeah i am running the ultegra shifters as well to get the top buttons, 105 FD/RD as its a crit bike and i dont really need the 1/2 second quicker front shifting which is virtually non-existent.

Thanks, I will run it as is for a bit and see how it goes. I’m coming from 10sp Ultegra with a 12-25 cassette and never really felt I needed anything lower. 34T is rather overkill around here. No way an Udi2 bike was in the budget, tho! Of course the chainrings are also different (smaller) vs my c…

[image] McFly: 34T is rather overkill around here. Can I humbly suggest you take a bike vacation somewhere with some climbing? :rofl:

That sounds like a good plan! I have seen stuff about the triple bypass ride in Colorado. I am sure I’d appreciate a 34T on that one.

[image] RONDAL: I can confirm that you can run the 105 di2 RD and a 11-30 ultegra cassette. I am doing it on my bike I just built up. It’s interesting you say this as I recently read somewhere that you CAN’T run 11-30 cassette (Ultegra) with a 105 Di2 derailleur. If I can find the article, i’…

[image] Gnome: fwiw theprosclosest has had helluva good deals on di2 lately I can confirm this WAS the case… though it may not be anymore (at least at this moment)… There was an “end of year” sale going on recently in which I picked up a 105 Di2 RD for $85 and 105 Di2 Shift/brake levers w/ca…

Per Shimano’s specs page : [image] But I always struggle to understand why this is an issue for the “MIN” side of RD specs. Using a cassette that tops out at 30t instead of 34t still has a range of motion that works fine with the smaller 30t. Depending on the method used to size a chain, you may …

Shimano’s spec page is CERTAINLY a great reference, but it was a 3rd party site/blog/forum somewhere I was reading… I also wonder if their specs may be conservative anyway… I remember reading at one point with 105 mech the MAX is 34t, but i’ve read articles where folks were saying you COULD stretch…

Yeah, people often push Shimano RD to larger low cogs than spec’d. The 34t you mention was likely related to the older 11-speed setups since the new 12-speed actually lists 36t as the max above.

105 di2 compatibility

Equipment

Will_Peters January 2, 2024, 9:38pm 15

It’s interesting you say this as I recently read somewhere that you CAN’T run 11-30 cassette (Ultegra) with a 105 Di2 derailleur. If I can find the article, i’ll post it here for reference, but cool that to know that it DOES work.

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105 di2 compatibility

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