Ultegra 8000 RD- max cassette

[sjbraun]

I’m curious to know real world experience with Shimano Di2 Ultegra rear derailleurs. Shimano recommends up to a 32 tooth large cog. But I know people have pushed that limit. What’s the largest rear cog that can be run without using a Road Link?

Thanks

[peanutgallery]

Definitely a 34 shimano dynasys cassette. Sometimes a 36, but that depends on the bike and hanger

[weiwentg]

Originally Posted by sjbraun

I’m curious to know real world experience with Shimano Di2 Ultegra rear derailleurs. Shimano recommends up to a 32 tooth large cog. But I know people have pushed that limit. What’s the largest rear cog that can be run without using a Road Link?

Thanks

I think 32 may have been the official maximum for the 6800 RD. I run one of those with an 11-34 cassette. They didn't make Ultegra-level cassettes with 34t cogs when 6800 was current, so who knows what the official max would have been.

The R8k GS (mid cage) is officially rated for a max of 34t, minimum of 28t. The SS short cage RD has an official max of 30t, minimum of 25t.

Edit: indeed, the mid cage 6870 RD had an official max cog of 32t.

[12snap]

I've run a 34 tooth cassette with a R8000 Ultegra SS rear derailleur. That was the non-DI2 version but I wouldn't expect them to be any different.

[dem]

36 works for sure and 40 if you don't mind a bit of a saggy chain and bad cog wrap and slightly slower shifting.

Just get the roadlink though - it makes everything better.

(tested on serotta nove + 10-40 XTR cassette, but I didn't ride it much more than around the block.)

[hairylegs]

I could never get road link shifting well - I tried it with a 38. Ended up going back to a 34 and it works great!

[Hilltopperny]

I am and have been running a 40t on my gravel bike for the past two years with the ultegra rd. I believe you could even get away with a 42t, but the shifting isn't as crisp as the 11-34t.

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[weaponsgrade]

I'm running an 11-40T with an Ultegra RX and 48/32 rings. I can shift into all the gears. Big-big works too but it looks and sounds ugly. After having spent some time riding, I'll give the shifting quality a 7 out of 10. I might try a Wolftooth RD extender thing and see if it gets the shifting any better.

[NHAero]

I tried a R8000 GS with an 11-40 XT cassette, and after fussing with the B screw it worked. Adding a Roadlink DM improves it noticeably.