Shimano Ultegra Di2 compatibility with 14-27 cassette

Hello. I ordered the new Trek Emonda SLR-7 with Shimano Di2 electronic gears. Unfortunately I cannot use the 11 speed cassette that comes with the bike and so I ordered an extra Shimano Ultegra 14-27 cassette. Does anyone have any experience with such a modification? I have no idea what kind of cage the bike comes with but I suspect it could be a medium. The size of the bike is Large. Many thanks to all who answer.

Based on shimano’s website the medium cage isn’t compatible with a 14 tooth small cog. However, the short cage is. If you scroll down on the following pages you can see the field “Top Sprocket_max” and that will give you the largest compatible small cog.

Short Cage:
https://bike.shimano.com/en-EU/product/component/ultegra-r8050-di2/RD-R8050-SS.html

Medium Cage:
https://bike.shimano.com/en-EU/product/component/ultegra-r8050-di2/RD-R8050-GS.html

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Interesting - what is it about a med cage that prevents a 14 cog min? My understanding was that having too big a difference between max and min cog was what would kick you over from short to medium cage, but I would have thought a medium cage could cover anything a short cage could.

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I believe the ramp angles of the parallelograms are different to better follow the narrow range and wide range cassettes between the two derailleurs. I’m guessing the med. cage would work with the narrow range cassette but might not provide as crisp shifts as the short cage.

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Quite right! Thanks so much for the input. Just for the record, the bikes does indeed come with a short cage (thank God!).

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Purely out of curiousity, why’s that?

The bike actually belongs to my 17 y.o. son and according to UCI rules for development athletes the maximum allowable stride is 7,93m. Having a chainring with 52T at the front, the only available option is a cassette with a 14T. This combination, along with 28mm tyres, gives a stride of 7,90m.

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Thanks, I’ve just learned something!