Direct Mount RD Hangers

Am I right to assume that Shimano and Campy RD’s that are compatible with direct mount hangers are also compatible with the same hangers? Or do the dimensions that Campy and Shimano spec for direct mount hangers differ?

Assuming a person has the choice of a standard RD hanger or a direct mount hanger on a custom frame, what are the pros and cons of each? Is one necessarily better than the other? I would think that if an RD is compatible with a direct mount hanger, the direct mount hanger would provide a more rigid mount than an RD which uses a direct mount link to mount to a standard RD hanger. Is that a valid assumption?

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Yeah…whether that added stiffness makes a meaningful difference, however….:man_shrugging:


Great questions. I’m curious about this too and may trial changing my Record 12 setup to a direct mount setup over the winter.


As far as I am aware the Shimano spec has become the industry standard, as is so often the case.

The DM hangers offered by major suppliers like Paragon Machine Works only come in Shimano flavours: S_Rd (44.7 mm) and S_Mtn (47.4 mm). I use PMW direct mounts on all my bikes unless the client requests a traditional mount, most of them have been built up with Campagnolo components with no problems so far.

On my personal bike I have a Chorus 12 rear derailleur mounted on S_Mtn spec hanger (to make room for a Rotor cassette with a larger range than offered by C) so it might be the case that these things aren’t as critical as people assume.


From my experience with a direct mount xt mech on a MTB I’d probably avoid it.

It sounds like a good plan to improve performance but I can’t tell the difference between 11 speed xt DM and 11 speed GRX on normal mount. It also seems like on the MTB front that the standard didn’t become very standard so I’m tied into Shimano for the foreseeable future, as my limited research shows SRAM won’t run on it.

I could get a new dropout but it’s hard to find and it’s a 8 year old frame so not good value.

In short without full frame builder adoption I’d skip it as it doesn’t provide enough benefit to me (YMMV).

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I’m a dummy. I should have looked more closely at my Chorus RD tech manual. It seems that Campy specs a direct mount hanger ∼47.46±3.5 mm long, so it would seem the Shimano mountain direct mount would be the right one.

Gracias, man.


Just my experience with my bike - the primary benefit of switching to the direct mount Shimano (GRX with a long cage) was to simplify wheel mounts. With DM, there is one less moving part and the derailleur stays a bit further back and out of the way when the wheel is off. An added benefit is that the shifting (mechanical, cabled) is crisper, especially under load. I believe that is due to the added stiffness of DM that comes from removing the bracket/link/axle from the derailleur. I vaguely recall Shimano claiming that the derailleur is positioned slightly differently, but that might just be about better alignment maintained by stiffness of the mounting. The only possible downside I can see is that there is one less link (a relatively thin plate of aluminum) in the DM than the standard mount. Because the hanger is itself a fairly thick piece of aluminum (Syntace X-12 hanger), it seems that would expose the frame to greater risk of damage in a crash. Maybe the hanger would snap before my Ti frame is damaged, but I’ve decided to address that issue by staying off the ground :slight_smile: Switching to the DM was as easy as swapping the hanger (simple hefty through bolt) and removing a mounting bracket from the derailleur.


Are you sure those lengths aren’t the other way around? I just found this document from Paragon Machine Works, and it seems to indicate that the Shimano Road DMs are 47.47mm long and the Shimano Mountain DMs are 44.27mm long.


You are right, I had them the wrong way around.

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No worries. Shimano doesn’t exactly make it easy to find such information.