Ultegra 6800 to r8000 compatibility?

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thecaptn
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Ultegra 6800 to r8000 compatibility?

Postby thecaptn » Sat Mar 31, 2018 4:08 pm

Hi all,

Does anyone know if 6800 and r8000 have the same pull ratio?

And is it safe to assume that they have different chainrings?

My current ride has 6800, I'm thinking about buying a spare racing bike and it'd be nice to be able to swap things about so I'm wondering if it were best to look for another bike with 6800 on it.

One last question, is the new version better, same , worse or just different?

Thanks,
Peter

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Duck!
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Re: Ultegra 6800 to r8000 compatibility?

Postby Duck! » Sat Mar 31, 2018 7:27 pm

The two groups are virtually completely cross compatible. The only thing that may rear its head on some frames is 6800 front derailleur on R8000 cranks. The new crank has the small ring located slightly closer inboard, increasing the space between the two rings, primarily to minimise cross-chain noise with consideration to slightly wider disc-brake hubs. Some frames with braze-on mounts may not allow the 6800 FD to swing in far enough; with the low limit screw wound right out there is a point where the derailleur linkage geometry will not allow it to retract any further. R8000 geometry allows the front derailleur to swing in a bit further to allow clearance for the more inboard small ring.

Chainrings are compatible, but the big rings are not a perfect cosmetic match.

Shifters and brakes are only minor improvements over 6800; derailleurs more significant. The Shadow rear derailleur design, used on MTB models for over 10 years, is much more stable, which reduces chain jump & ghost shifting if you do hit rougher stuff. The compact front derailleur design gives much better clearance for wider tyres, which would tend to foul the long-arm 6800. Both groups use the same chain, and cassettes are largely identical, just with some different ratio options in the R8000 series, plus the non-series HG800 11-34.
I had a thought, but it got run over as it crossed my mind.

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thecaptn
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Re: Ultegra 6800 to r8000 compatibility?

Postby thecaptn » Sat Mar 31, 2018 9:04 pm

Thanks Duck!,
I could live with that. Just keep the front derailleur matched up with the crankset and the rear derailleur matched to the cassette if using r8000 and 11-34.
Peter

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Duck!
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Re: Ultegra 6800 to r8000 compatibility?

Postby Duck! » Sat Mar 31, 2018 11:07 pm

In most cases the 6800 FD should be fine with the R8000 crank, but there may some oddities that won't suit. The R8000 FD will certainly work with the 6800 crank. Similarly, and which I only obliquely referred to, while 6800 is not incompatible, the R8000 crank is better designed to work with disc brake rear hubs.

RD-6800 can probably be made to work with the 11-34 cassette, but its clearance will be dictated by the particular frame's derailleur hanger. The long cage will be necessary, but have ample chain length to cover the slight increase in range over the 32T from 6800. I've successfully fitted short 6800s with 32T, but chain length gets marginal, and won't do the wider cassette, except maybe with a narrow-range CX crank with 36-46 rings, or a 1x.
I had a thought, but it got run over as it crossed my mind.

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