Do I Have the Right Rear Derailleur?
 

A while back I rebuilt my old Specialized Roubaix with an Ultegra R8000 11 speed compact groupset. It previously had an Ultegra 10 speed triple.

I selected the 50/34 compact crank.., and wondered about what cassette to get.

I read that the 11 speed 11-28 and 11-32 were pretty common choices, and then discovered that there is also an 11-30.

So, I went with the 11-30, and got the Ultegra medium cage rear derailleur.

It works fine, except when I am in the small front chain ring, and any of say the three smallest cogs in the back. Then, the chain sags, and in the smallest cog, the jockey wheel actually touches the frame.

now, in the smallest rear cog and the small chain ring, the cross chaining is pretty bad, so maybe that combo should be avoided anyway? but the next two smallest cogs out to be usable - right?

I think the B scew is correctly set, or maybe a bit tight - in the small chain ring, and the big cassette cog, the jockey wheel is no where near the cog.

I am wondering, if I should have the large cage RD.

I don't think I have too many links in the chain.

Here are two pics.

the first shows the bike in the big chain ring, and big cassette cog. I don't think I could have any fewer links.

the second shows the small chain ring, and the smallest cog. The chain is loose, and the jockey wheel is against the frame.

what am i doing wrong?


https://cimg4.ibsrv.net/gimg/bikefor...2279de0f1f.jpg
https://cimg8.ibsrv.net/gimg/bikefor...e922c01387.jpg

I'd make one or both of the following.

Adjust the B screw to push the RD lower.

Cut 1" from the chain (after confirming that it will still be long enough--- test by pulling the lower loop forward and hooking onto the bottom of the chainring).

Lastly, once you improve it slightly, accept that the small/small will have some sag as a compromise for everything else being good.

The 11-30 is messing it up with a chain too long because that is expecting a 1x up there.

You'd be able to remove one link with a smaller 11-28T, thus taughting the chain when it's on the 11T.

There exists aftermarket bolt-on dropouts that let's you place a RD even lower.

I will try adjusting the B screw.

But, I look at that first pic and think; there's no way the chain can be shorter...

with the cage horizontal, isn't it already as short as it can be?

or, am I not understanding it correcly?

The 30x50T setup is making the chain too long.

11-30T is practically a mtb cassette.

My fastest commuter has a 12-26T and I'm going to soon swap it to 12-23T to get more smooth gearing.

There's an easy way to confirm as I described earlier.

Shift to big/big. Pull the lower loop forward 1" (2 links) and hook back onto the bottom of the chainring, letting the excess stick out the front for the moment. Push up on the RD cage and confirm that there's still some travel left.

Another option that may solve everything. Find a larger diameter idler pulley. That will slightly increase the RD take up capacity, and hopefully, combined with B screw adjustment will allow the existing setup work fine, except possibly in small/small.

The chain length is correct for big/big, you shouldn't/can't shorten it. With luck cranking in the B screw will help clearance and tension on the small ring - if it doesn't go quite far enough you can reverse the screw so its head is hitting the frame.

Does anyone think a long cage derailleur would help?

This is how I do a quick check and keep the hands clean.
Put it on BIG:BIG and see how much "slack" you can pull.
Make sure you have "some".
https://cimg0.ibsrv.net/gimg/bikefor...7b6d7e1b47.jpg
IF you can't pull "enough", don't shorten.
It is what it is and you really don't want those extreme combinations anyway.

I don't understand all these "mtb gears" and "too short" comments. According to Shimano's website, the R8000 medium cage should handle up to a 34t cog with a chainwrap of up to 39. The OP's setup has a 35 chainwrap, so it should be well within reach. The picture makes me think the chain could be straighter, so take FBinNY 's advice and pull the chain tighter to see if it will work to take 1" out. If that doesn't work, I'd check the part number to make sure you didn't get a short cage in the wrong box or something.

https://bike.shimano.com/en-EU/produ...-R8000-GS.html

Two suggestions from someone who runs 12-30 cassettes with 48/34 cranks on several bikes:
1) Chain is too short in big/big
2) Don’t use small/small. In fact, I don’t use the bottom half of the casette at all in the small chainring.

Something to double check is if the RD is installed correctly. The attachment of the bracket axle unit (the upper link) to the frame's hanger looks a little more vertical than common. And also the cable housing entry angle looks a little more horizontal than usual.

See the pic, the hanger tab should be in the green position. Sometimes it is erroneously installed in the red 'gap' position.

https://cimg3.ibsrv.net/gimg/bikefor...6438c987fc.jpg

Pretty common problem when changing out components. For me all to common as I never have matched components. The solution is easy?

Stop Cross Chaining
Get a Long Cage Derailleur if not already using one
Take out a few links

Of course it would, but I thought you were trying to avoid spending more than necessary. You're so close, and can probably solve it for free with B screw adjustment, and/or for small $$$ with a bigger lower pulley.

In your shoes, I'd try to get it closer, then accept it since I don't ride small small, and the consequences of accidentally shifting to it are minor. My touring bike has a "bail out" granny which causes sag on all but the largest rear sprockets, but I happily accept it because all the combinations I actually use are fine.

I'm with you. I take "can't work" and "won't work" as a challenge

I step back and consider what would be needed for it to work, ie. slightly more chain take up. Than figure out how to make that happen.

This comes more naturally to me because I started serious riding before the internet or product documentation, so every build involved working from a blank slate.

To the OP

Challenge yourself to tinker until it works for you. The only serious sin is cutting the chain too short so measure 3x first if considering that.

If you want to see if a larger idler will help before buying one, jam something between the chain and puller to increase diameter where the chain leaves. Test the effect at both ends of the idler cage arc.

Likewise with B screw. Jam a small wad of paper between the screw and tab and see if it helps. if so, buy a longer screw or modify the stop tab.

Wow.., do I feel dumb...

I thought when I installed it that it looked weird.

And.., since i put on this RD, it has been _incredibly_ difficult to remove and replace the rear wheel - impossible without removing the quick release - the cogs just wouldn't go above the jockey wheel.

so, here is a pic of the way it was; looks just like the wrong way in your diagram - thanks!

i fixed it, and the interesting is that pretty much, the shifter indexing is still fine.

I think I need to look at the B-screw and the chain length again though


https://cimg2.ibsrv.net/gimg/bikefor...9032b23749.jpg

And, I've ridden 1000's of miles with it wrong

Yes, just move it into the correct position. All else should be good.

Disregard all the other unhelpful posts, DONE.

Does that second, incorrect protrusion/stop on the RD do anything except confuse people?

The number of ridiculous responses from people who have no clue but weigh in regardless was amazing. Great you were able to fix it as well as filter out the garbage.

Haha, don't know what is for, the MTB Shadow style RD that I've seen doesn't have it.

Guess that it would keep the bracket from rotating backward, but the bracket is supposed to be firmly attached to the hanger, with the proper tabs on each in contact.

11-30 is a Dura-Ace 9100 11-speed setup, https://bike.shimano.com/en-EU/produ.../CS-R9100.html. 11-28/11-32 was/still a common setup for Ultegra 11-speed. Current 12-speed offering is 11-30 &11-34, https://bike.shimano.com/en-EU/produ...-R9200-12.html & https://bike.shimano.com/en-EU/produ...-R8101-12.html.

11-30 as an MTB range dates back to the 8-speed starting from the early 90s.

People offering sincere suggestions to help a fellow cyclist is "garbage?"

Wow.

now, now...

I appreciate _everyone's_ efforts!

But, KCT1986 did spot the problem - so special thanks to him

funny thing is, i sort of always thought something was wrong - the angle was obviously different than the ultegra it replaced.., and the problem getting the wheel on and off was ridiculous.

But.., bikes are finicky, and it worked pretty well.., so I kind of figured it anything was really wrong, as in mounted incorrectly, it wouldn't work at all

anyway - after changing it i had to back out the B-screw a lot.., and I think the chain might be a little short.

There is a lot more tension in small/small, and the cage is still pretty horizontal in big/big, which causes resistance

11-30 is an 11 speed Ultegra R8000 choice as well - I have the ultegra

https://bike.shimano.com/en-EU/produ.../CS-R8000.html