Shimano R9150 RD - Why so few direct mount hangers?

Discuss light weight issues concerning road bikes & parts.
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Calnago
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by Calnago

Good eye @Turbokoo... and I thought exactly the same thing. Except... that's not where the hangup occurs. In all cases that I've seen where rear wheel removal is difficult, it's at the point below the hanger where you're trying to clear the upper pulley and the cog/chain. The derailleur just stops and physically can't move back any farther. This is the stopping point regardless of which hanger you use. And it's not the hanger that's getting in the way. It's the upper pulley, and since the derailleur should be in the same spot in space regardless of the hanger used, so is the upper pulley. So, the solutions thus far have been discussed earlier in the thread. Grinding some of the B-link away... I don't like this solution because I physically wrestled with the derailleur with not chain attached and I think the reason for those stops are simply that pulling the cage back farther than that puts such huge stress on the pulley cage that I don't think it would last very long.
The other solution, and the one that Team SKY is clearly using... is to just ignore where the derailleur would normally rest on the regular derailleur hanger stop and, against Shimano's instructions, rotate the B-link away from the stop so that it is horizontal to the ground, essentially placing it a bit further back in space. I describe that in this thread as well. And in fact, for this bike, which is small and the wheel is in fact a pain in the ass to remove... that's all the change that is needed. Doesn't look like it'd be much, but it doesn't have to be... it's enough. Trouble with that is you're relying solely on the torque of the mounting bolt to hold that derailleur in place, without the support of the hook on the derailleur hanger. In any case... the shifting is unquestionably superb, and all that chain wrap not only provides for better shifting, but by having more teeth engaged it also has to increase the longevity of the cassette as the driving force is distributed over a greater area at any given time. The cost for all this technological goodness... Rear wheel removal is more annoying for sure for almost all bikes, and extremely frustrating for some. Meh... I can live with that. But at least now I know why.

@Pdlpsher1's bike, has other issues related to optimizing his shifting, but these are all due to where his derailleur is in space, a possible incorrect chainlength, and possible adjustment factors, etc. Granted, his current hanger is spec'd for mountain bikes, but I think that difference alone is not going to resolve the biggest issue which is where, exactly in space, the derailleur ends up being positioned. His scenario, with 425mm chainstays and a frame/hanger arrangement which places the derailleur, in my opinion, way too far back and elevated from the Shimano spec, creates a situation where rear wheel removal is the least of his worries. I'm sure that rear wheel just drops right out. In fact I even said it looks like he could just pull it at a slight rearward and it would still come out, given how the dropout angle looks.

BdaGhisallo
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by BdaGhisallo

I spotted this over on CN. Looks like Bianchi went a different way than BMC, opting to go for a solid and chunky DM hanger.
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Bianchi DM hanger Groenewegen.jpg

by Weenie


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zank
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by zank

The difference between road DM and mtb DM is the road DM is 0.65 mm further rearward and 3.79 mm lower.

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Calnago
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by Calnago

@bdghisallo: That Bianchi hanger does look solid, and to the extent the ultimate connection from derailleur to frame doesn’t move or bend that’s a plus. When the B-Link first came out with the derailleur I questioned how much more leverage it would put on a regular hanger. And if that hanger was already on the soft side, then that could not bode well for shifting. Someone argued that it did not add any extra leverage from a physics standpoint but I couldn’t quite grasp that concept. The BMC hanger, when looked at from a dead on side profile looks super thin, but it’s structure when looked at from above is very thick and when considered from a 3d perspective it doesn’t look very susceptible to bending or twisting either. I’m presuming Bianchi is offering two hanger choices for this frame then, the hanger you showed as the option for the new Shimano derailleur and a different hanger for Campy or SRAM?

@Zank, thanks for those specs on the differences as to location of the road vs mtn hanger. And there’s one more in the angle of the hook coming off the bottom of the hanger, correct? That angle is different by 10 degrees which would also add a bit to both those numbers you presented as the derailleur, once mounted against the Road stop, allows the road version to rotate a little more forward than the stop on the mtn version would allow. Not sure it makes much difference but as I showed earlier in an example using a Campy derailleur, it was enough of a difference for Pilo Mfg to change their design when I presented it to them.
Last edited by Calnago on Sat Feb 10, 2018 2:21 pm, edited 1 time in total.

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zank
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by zank

Yes, you are correct. 35.5 degrees for road vs 22.5 degrees for mountain. Both are plus minus 2.5 degrees.

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Calnago
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by Calnago

Hmm, so I was assuming it was the other way around... with the bigger angle being for the mtn hanger. That changes what I just said then about the angle bringing the road position of the derailleur even more forward. It actually would make it stop more rearward than it would of attached to the mtn hanger, all else being equal.

[edit]: ignore that last paragraph I just wrote. I was visualizing the Campy hanger spec diagram which measures that angle from the opposite side. Just had a look at the Shimano spec again and yes, the difference will have the effect I described in my previous post.

rpowell
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Joined: Tue Sep 10, 2013 12:47 am

by rpowell

it really looks like if you changed the derailleur hanger side of the b-link from a fixed attachment to a pivot with some type of clutch then you could easily swing it out of the way when the clutch was activated but otherwise it would remain fixed. that would let you keep your short stays and snappy handling.
maybe im missing something in the geometry but it looks like you just need one mor pivot to get the pulley farther back.

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