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Old 06-05-21, 11:37 PM
Method to My Madness
Join Date: Nov 2020
Location: Orange County, California
Posts: 559

Bikes: Cannondale Synapse, Trek FX 2

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Originally Posted by Davidb67 View Post
So I finally got hold of 2 new CS R8000 Ultegra cassettes - a 12-25, and a 11-32T.
my Di2 6870 rear mech is short cage, so for now I put the cassette onto my wheel, and put the bike up onto the stand, turned the cranks and shifted up and down through gears, but avoiding the final 2 lowest - 30T & 32T so as not to foul anything up.
ive got a 17-20T jump, and although that shift isnít quite as crisp as the rest when changing to lower gears, it certainly didnít struggle jumping away until it ďcaughtĒ, more just a fraction of a second longer to jump on to the larger sprocket, than the others.
definitely looks workable but I donít know whether this running OK on the bike stand is in anyway similar to what I would find out on the roadÖ..if itís as Iím seeing, then Iíd be happy and prepared to buy the new 8050brear mech - medium cage.

be interested in peoples thoughts
Perhaps follow the OP's gearing: 12, 13, 14, 15, 16 (from the 12-25 cassette) and 18, 20, 22, 25, 28, 32 (from the 11-32 cassette) to avoid having a three teeth jump in the middle of the combined cassette.

Also, the largest two cogs should be 28T and 32T, so a short cage RD should have no problem shifting the chain onto the 28T (assuming appropriate chain length).
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