Hi everyone, I’m running into a UDH / SRAM Full-Mount interface issue on my Assisting Force AF01 frame and want to check if others have seen the same.
What I’m trying to install: SRAM Rival XPLR rear derailleur using the SRAM Full-Mount bolt kit (UDH Full Mount interface/bushing).
Observed problem:
The outer planar/relieved contact area around the rear axle on the frame is too small (see picture), so the flange of the Full-Mount bolt does not sit fully on the intended machined seat. Instead, the bolt flange partially rests on the surrounding surface (paint/step), meaning it’s not a full 360° planar contact.
Measurements (frame vs. hardware):
• Frame’s machined/relieved seat diameter: 24.5–24.7 mm (structural material and paint hight around the machined seat = t = 0.3 – 0.7 mm, see picture)
• Universal UDH Full-Mount bolt kit flange outer diameter (supplied with frame): dia. 25.0 mm
• Full-Mount bolt flange outer diameter supplied with my SRAM Rival AXS derailleur: dia. 27.0 mm (dia. 25 mm dropped off 0.3 mm, see picture)
So I see two issues:
Even the 25 mm flange from the frame-supplied kit does not fully sit on the machined seat (because the seat is max 24.7 mm in dia.).
The SRAM UHD busing bolt with 27 mm outer flange and 25 mm inner 0.3 mm dropped off flange does not fit full face contact either. (circular, not even rectangular contact on the painted surface)
Concern: If the flange clamps on paint/step instead of a true planar seat, it may settle/creep under torque (35 Nm) and could affect alignment, clamping force, or shifting consistency.
Question to the forum:
• Has anyone measured the outer seat diameter around the axle / checked full flange contact for the Full-Mount bolt?
• Did your frame have a larger machined seat (≥25 mm)
• Any reports of the same mismatch?
• Or is this simply not an issue?? I have inserted the busing and held the derailleur on the frame, there is still enough enough gap around the derailleur direct mounting clamp…