wayold

So I just mounted an oversize cassette on my road bike. Original equipment was R6800 Ultegra, 50-34 in front and 11-28 in back (but updated to 11-32 years ago). I just installed an R8000 RD and 11-40 XT cassette. Everything clears (with the B screw all the way in) and shifting is pretty crisp in all gears - no roadlink needed BUT the chain now makes contact with the FD in the lowest 2-3 gears on the 50T chain ring - and if I try to increase the cable tension on the FD cable I start making chain contact in the higher gears. It just seems like the width of the FD (still original R6800) is now marginally too small for the range of positions of the chain.

Now granted, using the lowest gears on the big chain ring is cross-chaining I probably shouldn't be doing anyway, but I'm wondering if this is a common complaint among those pushing to oversized cassettes on 2x systems and an indication that I should possibly upgrade the FD as well (or maybe just do a better job of tweaking the FD I have).

KerryIrons

The FD was not designed to work with that kind of cassette range and you have hit on the reason: the cage is too narrow. You could try simply bending the cage a little wider (it won't take much) or just vow to stay off the biggest cogs when on the big ring.

cyccommute 

To add to KerryIrons’ post, the larger gear in the back has moved the chain so that it enters the front derailer at a slightly higher angle than the 28 tooth cog. The derailer is slightly narrower as it moves upward as well. The chain is hitting places where it was never meant to be.

Additionally, not all front derailers are equal. One of the dirty secrets I’ve discovered in Shimano front derailers is that the higher end, “better” ones (105 and up) are too clever. Shimano puts in lots features into their high end front derailers to help with shifting like shift plates and raised sections that make close front gearing crisper. They are also narrower. Shimano’s lower end stuff (Tiagra and below) have been neglected with fewer shift plates and raised sections. They also tend to be wider. For wide range gearing, the cheaper derailers are a better, more forgiving choice. Tiagra, Sora, and Claris are actually a really good front derailer for wide range gearing. Microshift front derailers are also good choice. All of them are relative cheap.

wayold

Thanks guys. I kind of suspected as much, but I've seen other bikes (like my wife's 105 equipped Domane SL) get away with using an 11-40 with no rubbing in any gear, so I was hoping for the best. The idea of trying a Tiagra FD sounds good. I'll try throwing one on and see if I have better luck.

oldbobcat

Well, Tiagra, Sora, and Claris aren't made for 11- and 12-speed chains, so of course they're going to be wider. They also aren't going to index with narrower chains, either.

Kontact 

Who says they won't?

cyccommute 

If I had a nickel for every time someone tells me something “won’t work” when it comes to bicycles…

Sora, for example, has been for 8 speed systems. By your logic, it shouldn’t work for 9 speed since 9 speed is narrower chain. They work just fine on my 9 speed systems.

oldbobcat

First, which Sora are you talking about? Sora 3000 is for 9-speed. Run any generation of Sora with 11-speed, or Tiagra 4700, and get back to me.

oldbobcat

Have you run a Sora/Claris/Tiagra (pre-4700) front derailleur with an 11- or 12-speed STI? I'm curious.

cyccommute 

You are missing the point. 8 speed Sora works on 9 speed systems and 9 speed Tiagra will work with 10 speed systems. Various other front derailers will work with systems one gear (or more) removed from their “optimal” gearing. Some 10 speed front derailers will even work with systems one (or more) gears less than what they are designed for. The front derailer isn’t as sensitive to chain width as you make them out to be. I’m unlikely to test this under your conditions because I don’t own any 11 or 12 speed systems but I have done it many, many, many times with 9 and 10 speed systems without issues.

Let’s also not miss the forest for the trees. wayold is using an 11 speed front derailer and it isn’t working properly. Why not experiment with something else that has worked in the past? Front derailers are relatively cheap so the cost out of pocket for the experiment isn’t going to break the bank.

CliffordK

You might also try one of the cyclocross front derailleurs such as the CX70.

That derailleur comes with either a top pull or down pull varieties, so get which you need for your application.

oldbobcat

I'm going from my experience mixing 8, 9, and 10 speed systems for customers a few years ago. Generally, narrow cages with wider chains could be compensated by loosening the cable a little, but then they wouldn't trim properly. Any degree of cross-chaining introduced rub. And wider cages with narrower chains were just slow to pick up and often resulted in missed shifts or double-shifts, depending on where the chain was on the rear cluster. And how the light-throw, low-trim pull rates of the new levers works with old derailleurs is anybody's guess. But experiment, have fun, and I'll butt out. Bye.

Kontact 

They shouldn't be compatible - long pull vs. short. But I haven't bothered trying.

Kontact 

I use a 10 speed SRAM Red derailleur with an 8 speed chain and don't need to trim across most of the range. But if you want to ride in cross overs...

squirtdad

r8000 derailler is specced for 34 max rear cog , 39 teeth of wrap and 16 teeth difference in front derailer.

OP setup is 6 more teeth than max rear cogs and 6 more teeth than chain wrap max (assuming the

RD-R8000-GS medium cage)

no surprise there are some issues

wayold

Just for thread closure, everything works now. I just needed to be a little bit more careful with setup. In particular I unbent a mildly tweaked derailleur hanger, readjusted the RD and added a tiny bit of cable tension to the FD. Apparently I could be pretty headless about setting everything up when I had an 11-28 or 11-32 in back, but the error margins are unsurprisingly tighter with the 11-40. I'm probably the millionth rider to successfully get the 11-40 and 50-34 to work together with R7000 or R8000 derailleurs, so not a big deal - just a bit more precision required in setup.