I just finished assembling a bike with a RD-R9150 derailleur, a 11-32 Ultegra 11s cassette and a 50-34 chainring.
I know that the RD derailleur only supports up to 28T cassettes so I’ll base my observations on the penultimate cog
When the chain is on 50-28, the chain looks correctly tensioned and if I removed one more link it would be too short.
When I’m on 34-13 (the lowest Di2 allows me to go when the small front is selected), the rear cage sits on its stop and the chain is loose.
Did I mess something up with the installation of the RD, so that it sits in the wrong position maybe?
The RD was previously on a bike with a 46-36 crankset: maybe it’s a smaller cage version that I need? But I though that all 9150 were the same short cage version, with a 33T capacity.
One peculiar thing I noticed is that I didn’t have to screw all the way in the B screw to clear the 32T cassettes, contrary to what I was expecting.
Any ideas? Thanks!
by sireatalot
7 Comments
Chain too long. OR there’s often like a washer type thing that goes onto the derailleur Hanger that kinda pushes it up.
https://preview.redd.it/f7dhg7cgg0rg1.jpeg?width=430&format=pjpg&auto=webp&s=603b946cc2f55b74d52039529cfd9e9940a143e0
So there should be this free spinny thing that has a notch sticking out.
You should never be in small ring small cog
If the wrap capacity isn’t exceeded, then it’s a setup issue with the RD.
Capacity of the Rear derailleur is exceeded. Perhaps you installed a wider range cassette, or different chainrings?
Or it’s just not installed correctly and isn’t taking up the slack chain as it should.
The RD-R9150 has a chain wrap capacity of 33t with the largest cog maxed out at 30t.
Your setup is currently at chain wrap of 37t and you have also exceeded the largest cog.
here is the official spec sheet for your R Derailleur
[https://productinfo.shimano.com/en/product/RD-R9150](https://productinfo.shimano.com/en/product/RD-R9150)
clearance of the low cog via the b-limit will just mean shitty shifting when in smaller cogs, as the guide pulley will be far away from those, thus creating harsh and unreliable shifting, especially under load.
No big, big cog for you, or little, little cog. Take out a link, maybe two, should be grand.
Check you b tension screw is setup right. I do this all the time on some of my setups and never big big, little little or I drop a chain.
Always best to reset the B screw when installing a new chain, and then tighten the B screw for slack in the extreme combination (2nd photo). Normally you should not be in an extreme combination, but you also don’t want to have a slack chain.
1. Attempt to increase B screw to remove slack. If that doesn’t work, reset b screw then…
2. Remove a link from the chain. You still have enough bend in the RD to remove a link and see how it handles that. Repeat step 1, and if that fails replace the rear derailleur with one that has higher capacity to err on the side of safety.
I know this is the empirical process. You should refer to manufacturer specs first before you dare to live dangerously.