FD spacer to run GRX chainset with Ultegra Di2

[ultyguy]

Quick one, got tired of digging. Thinking of a build with Ultegra di2 12 speed I have but using a grx810 2x 48/31 chainset that’s lying around. I take it I need to space out the Ultegra FD to make this work, what do I need to accomplish this and will the chain line suck or will it roll?

Thanks!


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[harblhat]

There's no spacer I'm aware of that will move a FD outwards. Depending on the frame you may be able to push the Ultegra FD limits out enough to work with the GRX crankset. Others have done so.

Note that the 12s FD throw is shorter as the rings are closer together, so even if you get the chain line out the shifting will not be perfect.

[BLachance75]

I was able to run a 105 di2 FD with a GRX 48/31 crankset. I had to trim the FD all the way out in the app to get it working. The shift from small to big was rough at times and also not reliable. I ended up getting a GRX 825 FD and it works perfectly now.

[satanas]

Try it first - it might be okay, depending on the frame's FD mount placement, etc. It's also possible to shim the GRX chainwheels inwards; somebody here does that to get better front shifting and different ratios with AXS.

[SummitAK]

If your frame has a bolt on front derailleur mount you could shim the mount out a couple mm.

If your frame uses a round tube clamp-on FD mount there are eccentric shims available that you could use with an oversize clamp to shift the FD outboard.

[ooo]

You can find braze on mounts for round seattube for wide spacing:

SRAM Wide Spacing Braze-on Adapter
Clamp size: 34.9mm or 31.8mm
Manufacturer Par Number: 11.7618.000.002 & 11.7618.000.003

K-Edge Braze Adaptor Clamp (they don't list offset, but all k-edge braze-on adapters have offset, it was made for chain catcher)

FSA FD012 - Front Bicycle Derailleur Adapter Clamp (Tandem Front Derailleur Adapter Clamp)

[bigfloor]

Running R8170 with my Canyon Grail2, GRX620 chainset and 105-DI2 front deraileur. Works perfectly

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