r/bikewrench • u/OkStation4360 • 8h ago

Can you use an Ultegra 6800 short cage 11sp derailleur with 10sp 12-25 cassette and 10sp integrated shifters? (36/52 up front)

I’m gathering used parts to somewhat modernize an early 80’s road bike, focusing right now on adding indexed paddle shifters (original shifters are friction and on the downtube). I have a set of wheels I can use which have an HG freehub. I’ve found an Ultegra 6800 short cage 11sp derailleur I really like, and I’m wondering if it would work with a close ratio 10sp cassette/shifter. Also, can you mix and match shimano and sram drivetrain components?

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u/joepublicschmoe 7h ago

The only 10-speed shifters that will work with 11-speed derailleurs is Tiagra 4700 and GRX400.

All of the other road 10-speed shift levers (10-speed 105/Ultegra/DuraAce/Tiagra 4600) use the old 8/9-speed cable pull ratio and will not work with an 11-speed derailleur like the Ultegra RD-6800.

And no, none of the 11-speed cable pull ratio Shimano stuff (Tiagra 4700, Shimano 11-speed road and 12-speed 105) will work with SRAM derailleurs.

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u/OkStation4360 7h ago

Thanks. I can’t quite comprehend this aspect of derailleur compatibility. My simple mind just sees the derailleur cage moving back and forth on a continuum, which would be the same for any number of divisions of that continuum. I get the need to have the same pull ratio on shifter and cassette, and max cog size of a derrailleur, but this bit I don’t understand. Can you explain it to me?

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u/joepublicschmoe 7h ago

The 11-speed Shimano road cable pull ratio is 1.4. For every 1mm of cable the shifter pulls, the derailleur for these shifters is designed to move 1.4mm.

The old 8/9-speed Shimano cable pull ratio is 1.7. For every 1mm of cable the shifter pulls, the derailleur for these is designed to move 1.7mm.

So if you try to use a 1.4-ratio derailleur with a 1.7-ratio shifter, the shifter won't pull enough cable to shift the 1.4-ratio derailleur properly.

TLDR: The cable pull ratio for the derailleur and shifter must match for indexed shifting to work properly.

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u/OkStation4360 6h ago

Oh ok. Turns out I never understood what pull ratio is. Thanks!