Di2 12-speed Ultegra 8100 and 11-36 or taller

I have a Trek Domane with 8100 Ultegra on it. I swapped the front crank to a Rotor ALDHU 50/34 w/ 155mm and want to increase the rear cassette to 11-36 from 11-34. I found Rotor makes an 11-36 although I can’t find it anywhere. What are my options if I’m willing to change out other parts to get something even bigger cassette-wise with Di2 like 11-40? The application is climbing mountains, with artificial joints. Cadence is everything. Thanks for any help.

CJ

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Ultegra and DA only officially support a maximum of 34t cassette, although I don’t think I hae heard of anyone having problems with a 36t. 40t may be pushing things a bit, but should be doable, especially with a Wolftooth Roadlink. Will likely need a longer chain too.

The new 105 7100 officially supports 36t, so is probably more 40t friendly, but getting your hands on it at the moment would be difficult.

Also consider perhaps swapping the 34t inner for a 33t inner for a few more rpm (not sure if this is possible with Aldhu?)

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Thanks. The Wolflink doesn’t work on 12 speeds they told me. Will try the 11-36 Rotor cassette, if I can find one that is…

Thanks, Chris

From what I hear, Shimano RDs usually accept cassettes that are a bit larger than officially specified. So Rotor’s 12-speed cassette will probably work, but I haven’t tried that. Rotor’s cassettes are from what I hear a thing of beauty. I have an oval chain ring by Rotor on my mountain bike and that is beautifully machined. Rotor even included gorgeously machined bits to screw the chainring into.

They are soooo much easier to mount than those damn “decorative“ XTR counter parts. The latter are a better fit visually, but getting them in straight … and they four separate, non-interchangeable. Who thought this was good design :face_with_symbols_over_mouth:

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Another option is to buy a super compact front chainring. I also have the rotor crankset myself, and you can buy 110bcd four hole chainrings made just for climbing. On the cheap side, there’s these Stone 46/32 chainrings that will work.

Check out this video where the topix gets explored

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That looks like an interesting video. I decided to order the Rotor 11-36 cassette (found one in Germany) and a KMC DLC12 chain and see if the Di2 (and knee and ankle) will tolerate these. Thanks for all the great advice.

CJ

I have a 110 BCD Rotor 3D+ crank set, and was able to put a subcompact 46/30 set of chainrings on it for some very steep hilly rides. Everything worked just fine.

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