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I would like to know whether I can use a 11-23 11-speed shimano cassette with the RD-R8000 11-speed Ultegra Shadow Rear Derailleur (short cage).

I ask this question because I see the new 11-speed Shimano cassettes no longer come in a 11-23 gearing.

Looking forward to your comments.

Thanks

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No, not according to Shimano, anyway. The Shimano specs pages are here, and this is the road rear derailleur page.

The specified RD-R8000-SS minimum low sprocket size is 25 teeth.

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Probably you'll be just fine, although it's technically outside the spec'd range.

Per the Shimano 2019-2020 Products compatibility Information document (warning: PDF link), the RD-R8000 rear derailleur is compatible with all of the following cassettes:

CS-R9100
CS-9000
CS-6800
CS-5800
CS-R8000
CS-HG800-11
CS-R7000
CS-HG700-11

As far as I know, that covers all of Shimano's 11-speed road cassettes, and I'm assuming Shimano doesn't produce an 11-23 MTB cassette.

BUT

The RD-R8000 is spec'd as

    RD-R8000-SS
(25T≤CS Low gear≤30T)

(the GS is similary spec'd with a 28T minimum)

so a 23-tooth sprocket would be slightly too small per Shimano's specs.

But it should work for you as Shimano's spec's are notoriously tight - and I already do have an 11-23 on a bike with an RD-8000-SS and it works fine with an 11-23. (I didn't even know it wasn't "in spec"...)

The page the info was extracted from:

enter image description here

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  • 28T minimum? Are you sure? The minimum is usually 11T for Shimano RD but for short cage, MAXimum is 28T, for middle cage (they existed) it was 32T and for long cage it is 34T Road derailleurs. In the 11-28 cassette there's a 23 so why should 11-23 not be compatible? – Carel May 9 '19 at 13:03
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    @Carel On page 17 of the PDF linked, both the RD-R9100-SS and RD-R8000-SS are spec'd as "(25T≤CS Low gear≤30T)", while the RD-9000, RD-R8000-GS, and RD-RX800-GS are spec'd as "(28T≤CS Low gear≤34T)" So for SS short cage, the latest 11-speed rear derailleurs are not spec'd to work with any cassette with a large sprocket smaller than 25t, and the long-cage GS derailleurs are not spec'd to work with a cassette that has a large sprocket smaller than 28t. Will they work in reality? Probably, and probably quite well. But the specs are clear. – Andrew Henle May 9 '19 at 13:13
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    @Carel (cont) The RD-8000-SS page has both "Low sprocket_Max. 30T" and "Low sprocket_Min. 25T". Seems crazy, but that's what Shimano says. – Andrew Henle May 9 '19 at 13:15
  • @Andrew Henle Thanks for your answer!!! very, VERY enlightening! – Alejandro May 9 '19 at 14:33
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    Shimano says many strange things in their data sheets. I've been running for two years and over 10.000km with UltegraDi2 with a 52-34 front without trouble (you shouldn't according to S.) and various rear cassettes 11-25, 11-28, 11-32. I'd try an 11-23 if I had one. Chainlife >3000km. I'd say their datasheets are ultra-cautious. – Carel May 10 '19 at 19:34

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