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My Ultegra R8000-series (Di2) front derailleur has a capacity of 16 teeth (I believe) and it currently has 52-36 chainrings.
What would happen if I replaced the inner with a 34t chainring?
I presume I don't need to add or remove chain links for such a small difference and that I may have to adjust the derailleur height (which may compromise shift quality) but will the derailleur actually be able to switch rings without exploding?
I'm looking at a relatively cheap way of reducing the gearing for some big hill climbs and the outer front chain rings are stupidly expensive.
I don't race so not overly bothered about fastest or smoothest shift quality - I'm more interested in dropping down to granny gear then spinning for a couple of hours!
Usually, the chain ends up bouncing off the bottom of the cage
If you leave it in the same place to cover the big ring, then my suspicion is that the chain will drag on the mech (the horizontal plate at the rear ofbthe mech) when in certain gears when using the small front ring.
So an annoying scraping sound
There might also be an issue when changing up. If the 50/34T and 52/36T are only made to work with each other then the shifting ramps might not be in the correct place.
It might be more prudent just to buy a compact chainset and sell the one you have.
If you leave it in the same place to cover the big ring, then my suspicion is that the chain will drag on the mech (the horizontal plate at the rear ofbthe mech) when in certain gears when using the small front ring.
Yeah, good point. I'm guessing this isn't a viable permanent solution though I'm intending this to be a temporary solution for a holiday in the mountains where I'm likely to also be using the biggest cog of the cassette so maybe the chain won't drag in the small ring/big cog combo...
I guess it's a cheap option to try out (cheaper than a new cassette and obviously cheaper than replacing both chain rings)
It might be more prudent just to buy a compact chainset and sell the one you have
Unfortunately (?) no as it's also got a dual sided crank arm power meter...
I suppose when it comes time to replace the outer chain ring, I'll do both at the same time and put on a 50/34 combo.
What's going on at the other end? Are you at max capacity of your rear mech for your cassette already? I'm a bit of a fan of my Miche cassette with it's individual sprockets. Mixing massively different amounts of wear not withstanding you can swap sprockets around - 11 or 12t-27t most of the time and 13 or 14t-32t when you need it. Or just get a cheap 11-32t cheap old skool MTB cassette. In my experience rear mechs are more forgiving that front of pushing specs.
What’s going on at the other end? Are you at max capacity of your rear mech for your cassette already?
Theoretically, yes, I'm at max capacity already (11-30 11 speed). I *think* I've got a R8050-SS rear derailleur though I can't see any markings on it to confirm it is short cage rather than medium cage (R8050-GS).
The cage seems to be around ~73mm between pulley wheel axles. No idea how to confirm whether that is short or medium cage...
Just thinking aloud, is it possible to change the inner and outer cages to switch it to medium cage, giving me more capacity?
Couldn’t you use a wolf tooth road link to use a bigger rear cassette.
Either the outer cage catches on the big chainring, or the chain runs on the bottom bar of the cage - triple cages are deeper and have an offset on the inner cage to compensate. I’d check Shimano Tech docs to see if you can buy the longer GS jockey cage plates for your rear mech. A drop hanger might not work as you’ve still not got enough capacity to take up chain slack - a bar-tight chain can jam and trash a drivetrain and frame very easily.
https://bike.shimano.com/en-EU/product/component/ultegra-r8050-di2/RD-R8050-SS.html
There's a part list with an exploded diagram but I'm not entirely certain that the cage is interchangeable, so a trip to my LBS may be needed...though I guess, it might be less expensive (or at least easier) to just replace both chain rings as I won't need to change the cassette
@vlad - I've got a 34T ultegra chainring going spare if you want to give it a try and see what happens ?
Cages are also interchangeable - they are held on by a grub screw (hence how it's so easy to swap in a carbon / giant jockey style cage)
I'm running a front mech on a system that exceeds it's capacity (small front ring is too small)
It rubs on the bottom bar of the cage if i cross chain. (small ring/small sprocket)
So i don't do that.
I can use from about half way up the cassette without any issues.
The chain would probably go slack if i went full small small, but i've never done that, so i don't know.