I’ve put a CS HG800 11-34 11 speed cassette on my ultegra 6800 wheel, along with the higher capacity RD8000 GS derailleur. Problem is the cassette is actually made for a 10 speed mountain free hub so requires a spacer to work on an 11 speed road free hub. I got all that to work fine in the rear, but the spacer moves the cassette way out to the right and now the chain rubs on the front derailleur when in the smallest two cogs. I cannot adjust the front out anymore.

It seems the ideal fix would be to put on a 10 speed freehub, but the question is, which one? I tried a 10 speed Dura-Ace 7900 (which uses the same 14mm bolt) but it does not fit the Ultegra hub - the spline diameter is different. Does anyone know if a 10 speed mountain free hub like the FH-m8000 fit the Ultrgra hub? Or some other solution.

Just one other comment: why does Shimano make so many variations of freehub splines when they all do the same thing!?!?

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    The spacer can't move the cassette out too far - there's not much spare space on an 11-speed rear end at all. So you probably don't need much of an adjustment to the front derailleur at all. Can you lower the front derailleur some - that would move the chain contact higher on the derailleur cage, which is farther forward and might give the extra clearance needed to avoid chain run. Alternatively, you might be able to angle the derailleur slightly differently. Angling the rear of the cage farther out would also give some more clearance when the chain's on the smaller cogs. Aug 7 '19 at 9:44
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    I suspect there's no 10s freehub that fits that wheelset, although I haven't checked. Do note that when you're in the small front ring and the smallest 2 cogs on the rear, chain rub is pretty much normal. You can ameliorate chain rub by trimming your front derailleur - push your left shifter in just a bit until you feel a soft click, but not until you fully shift. And in fact, it's not really recommended to ride in small-small. Your chain is at a steep angle, so your chain wears faster.
    – Weiwen Ng
    Aug 8 '19 at 11:13
  • This is when in the large front ring and when using smallest two cogs in rear. Not the small chainring and small cog Aug 10 '19 at 2:33
  • To clarify, the cogs are way outboard due to required spacer. When using the large chainring and smallest cogs the chain-line is too far out and the chain rubs on the outer plate of the derailleur. I can’t adjust the front d outboard anymore because 1 it would cause the chain to over shift off the large chainring and 2, the crank arm hits the derailleur. So the only solution is to move the cassette back to a normal chain line, ideally with a narrower free hub body. Aug 10 '19 at 2:38
  • Andrew, maybe so... Aug 10 '19 at 2:41

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