i have a shimano 5800/ 105 shifter laying around that i'm thinking to use on my CX which already has a SRAM XO 10 speed FD & RD.

first of all, would that even work, in terms of pull ratio, should be no problem?

if so, for RD, can i get it to index to a 11 speed cassette as needed or can only index to 10 speed as limited by the RD?

thanks.

An 11-speed Shimano shifter won't work with your 10-speed SRAM derailleurs. The cable pull ratio isn't the same, so it won't index properly. You could make the SRAM rear derailleur work with a Shimano 11-speed shifter by using a Jtek Shiftmate, but the Shiftmate almost costs as much as a 105 rear derailleur so why bother?

...and do you have a freehub on your rear wheel that'll take an 11 speed cassette?

It's the shifter that determines how many speeds you can shift; the derailleur just goes where the shifter tells it to. So if you managed to pair those parts, like by using a Shiftmate, it'd be an 11 speed setup.

thanks skydog.... i do have a freehub on my rear wheel that take the 11speed cassette. well i also have a 105 11sp RD... but since it's going on my CX, was hoping to use the SRAM RD to support cassette like 11/36, since the crank will also be a 105 mid compact.

this 5800/105 shifter, FD, RD, 11/28t 11spd group came off of my BMC TMR02. was trying to sell the group.. but too many lowballers for new component that's just taken off of a new bike.. so figured might as well upgrade my CX with it.

with the 105 RD.. is the largest cassette it till support is up to 30t only? sorry for the silly question.. all of my bikes are with SRAM.. it's been a while since I've used Shimano.

Your BMC TMR02 had a short-cage (SS) rear derailleur, which works with a 28t large cog. You may be able to get it to work with a 30t cog if you tune it properly, but it would be very unhappy with an 11-34 cassette.

A 5800 medium-cage (GS) rear derailleur accepts a 32t large cog, and could probably be tuned to work OK with a 34t.

I use a medium-cage 10s Rival RD on my 'cross/gravel bike. It's rated for a 32t but works OK with an 11-34.
10-speed SRAM is cross-compatible between road and MTB, so I could use a long-cage MTB RD if I wanted to.

Shimano 11s road has no MTB cross-compatibility (without shift adapters), so 32t is the largest (official) capacity when using a 5800 shifter.

thanks Tim.. hence that's why I switched over to using SRAM in 2011 and never looked back. i just love the Road/MTB cross compatibility SRAM offers and never have to worry about different pull ratio and what not.

thank you for the info on the 105 RD. it's brand new parts removed by my LBS after i bought the BMC TMR02 earlier this month. i wouldn't mind trading this groupset for a 10 speed SRAM Force. it comes with new shifters, FD, RD, BB, mid-compact crank, chain, 11/28t cassette (missed it in the photo) and 1 front brake, since the TMR has it's own BMC rear brakes that i'm keeping.

I like big cassettes and I cannot lie...

Yes, I also appreciate SRAM's road-to-MTB cross-compatibility, at least for 9 and 10 speeds.

However, their 11-speed (and now 12-speed) MTB and road drivetrains aren't cross-compatible any more; their MTB stuff has a different cable pull now (X-actuation).

tim.. i hear ya... "I like big cassettes and I cannot lie...You other brothers can't deny".

yea it's unfortunate on their 11sp moving forward.. that's why with my BMC i'm building her up with 10sp RED. cuz at least that still works with some of the RED22 stuff.