I have a custom drop-bar mtb/gravel steel frame with 32 inch wheels and 13s SRAM Force XPLR. Many things in the build are outside of standard SRAM specs and I’m in a dead end while troubleshooting one big issue. The derailleur cage is slightly touching the spokes when on biggest sprocket 46T.
The specs:
Chainstay lenght: 490mm
Front chainting: 34T
Crankset: Force E1 XPLR wide, 47,5mm chainline
Rear hub: Hope 5 pro, 12x142mm XDR
Rims: Nextie Premium Carbon 32, Rim Height: 30mm
Spokes: Sapim round j-bend 2.0-1.8 (custom order by the wheel builder so I guess length > 310mm).
Spoke tension measured with ParkTool TM-1: 117-130 KGF so just about at limit of the rim - 130 KGF.
Initially I’ve used 126 linked chain (by extrapolating SRAM chain lenght guide), used standard setup cog (6th gear). Shifting is flawless but the spokes do “ding, ding, ding” when putting any bigger power while on the largest cog.
I’ve tripled check the derailleur setup, redo it a couple of time with no change. Finally I’ve tried to experiment.
I’ve played with chain length (adding/removing 2 links) and I got slightly better results with 124 links and using 8th cog for setup. The idea behind this move is to lover the upper pulley mounting thread to extend the distance between the cage and spokes. I feel like the solution is partially nullified by spoke bending more as it further away from fixing point (hub).
A few more pictures from setup with 124 chain links (-2), and 8th setup cog (+2 than standard):
I’d be curious to try a different wheel, if the derailleur/chain tweaks aren’t working. Hub spacing/spoke lacing might make a difference. Might not have many other 32” options laying around though.
You’re probably the first person to have this problem…thanks for trailblazing! Sounds like a cool bike, show us the rest of it!
It looks like the “pulling” spokes are outbound, which pushes the spoke crossing towards the cage under power. Changing that would require a wheel rebuild, however.
Thank you all for responses. Looks like finding a hack that gets the job done is my best bet. I’ve ordered 1mm cassette shims and will try to trim down the cage with sand paper a little bit.
I’ll try it before relacing the wheel (preferably with boost hub which I avoided due to lack of compatibility according to SRAM manual ).
@Andrew1 Here’s a sneak peak into the project. I should probably make a separate post about the bike. Thanks!
Cassette shims aren’t a bad idea; if it’s just that much sound and only under power you’re probably pretty close to being okay. Honestly, Transmission likely wasn’t designed for 32” wheels; switching back to Eagle AXS might give you the adjustability you need to make this work.
How much space is there between the biggest gear in the back and the spokes?
CX-Ray spokes or similar would give a tad more clearance as they’re thinner laterally. FWIW, this was a fairly common problem with Dura-Ace 8 speed, and fixes included oval spokes, orienting the pulling spokes in the hub so they pulled the trailing spokes in rather than out under power, and grinding any inward protrusion off the pulley mounting bolt.
With other than T-Type you could try shimming the cassette out slightly too, but given the non-adjustability this may be impossible. You could also try fitting a Garbaruk 13 speed 10-52 cassette, which would move the cage further from the spokes in bottom gear. (These are meant to work with the XPLR RDs with a little tweaking, explained on their website.)
Just in case it wasn’t clear for everyone reading this, and I didn’t see it stated, the issue is an unintended consequence of the larger 32” wheel. The spokes take a closer to vertical path to the rim, so the right spokes are simply going to be closer to the derailleur. It’s a strong case for wider hubs when moving to 32” wheels. The somewhat rare but already established 157mm standard might suffice.
I second the use of thinner spokes and reorienting the lacing so that the heads-out right spokes are trailing. It also looks like the spokes are insufficiently “set” at the crossings. Setting them more firmly will give them more clearance and reduce their position change with torque.
Some more details on this bike, especially geometry, would be awesome. As I’m designing a 32” gravel bike of my own I’m very interested in your choices regarding bb-shell width, chainstay length, seat and head tube angles and trail.
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