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!?!?