UDH and SRAM Full Mount gravel frames: what fits, and what to check on a used bike

UDH and Full Mount are not the same thing

SRAM separates the two terms (SRAM):

• UDH (Universal Derailleur Hanger) is a standard hanger and the frame interface it fits. SRAM introduced it in 2019. SRAM says a UDH frame can take either a traditional derailleur on a UDH hanger, or a Full Mount derailleur that replaces the hanger.
• Full Mount is a way of attaching the derailleur. The derailleur mounts directly to the frame, over the drive-side dropout, centred on the rear axle. SRAM lists Eagle Transmission and RED, Force and Rival XPLR AXS as Full Mount derailleurs.

SRAM's case for Full Mount is alignment and strength. Because the derailleur is located on the axle rather than on a separate hanger, SRAM says it gets easier setup, better shifting under load and more resilience to impacts, and it "eliminates unnecessary adjustment screws." (SRAM)

The rule that follows is short. SRAM says Full Mount derailleurs mount to frames that use the UDH interface, and if your bike has a UDH, "your bike is ready for any of SRAM's Full Mount derailleurs." (SRAM)

Having a UDH is not the whole check

For Force XPLR AXS, SRAM adds conditions beyond the dropout (SRAM support):

• Gravel frames with a UDH-capable dropout are compatible.
• Chainstays down to 415 mm are endorsed with a 47.5 mm chainline.
• Chainstays between 405 and 415 mm can work with a standard road crankset at a 45 mm chainline.
• Rear suspension designs where chainstay length changes are not supported.

Then there is the rest of the drivetrain:

• Cassette and chain. SRAM says the XPLR AXS 13-speed Full Mount rear derailleur is only compatible with XPLR 13-speed cassettes and road Flattop chains. (SRAM)
• Freehub. The 13-speed RED XPLR XG-1391 cassette is listed as compatible with the XDR driver body. (SRAM) If your wheels have a Shimano HG freehub, you will need an XDR body or different wheels. Our smart trainer compatibility guide covers the same issue on the trainer.

Gravel frames whose makers state UDH

These frames have "UDH" on the maker's own spec sheet or product page. That is the only test for this list. A frame not listed here may still have a UDH; we just did not find the brand saying so.

Two cautions on this table.

First, UDH is a frame feature, and SRAM's extra conditions still apply. Check chainstay length on the brand's geometry chart against the 405 to 415 mm figures above.

Second, generation matters. Our checks cover the generations named. Older frames under the same model name may use a different hanger. Specialized states "UDH dropout" on the Diverge 4 FACT 9r carbon spec we checked. We did not check the alloy Diverge 4 spec line by line.

How to tell if a frame has a UDH

SRAM gives three steps (SRAM):

1. Look for the UDH logo on the hanger's mounting bolt. SRAM imprints "UDH" on all its own hangers. Some brands make their own UDH hangers, so no logo does not prove there is no UDH.
2. Check SRAM's online tools. For gravel and road, SRAM points to its Bike Finder.
3. Ask the frame maker. SRAM says the manufacturer "knows best."

UDH hangers are sold at SRAM dealers worldwide, according to SRAM. (SRAM) A non-UDH frame usually needs its own brand-specific hanger. That is one reason a UDH frame is easier to live with on the road.

Used-bike buying checklist

Use this before you pay for a used gravel frame you might want to run 13-speed XPLR on. It is a checklist of questions, not an inspection guide. For frame damage, have a shop look at it.

The frame

• Get the exact model, generation and year. Ask for a photo of the serial number or the original receipt.
• Find that generation's spec sheet on the brand's site and look for "UDH." If the brand no longer lists it, ask the brand.
• Look at the rear derailleur hanger bolt for the "UDH" mark. No mark is not a no (see above), but a mark is a good sign.
• Check the chainstay length on the brand's geometry chart. SRAM endorses 415 mm and up with a 47.5 mm chainline, and 405 to 415 mm with a 45 mm road chainline. (SRAM support)
• If the frame has rear suspension that changes chainstay length, SRAM does not support Force XPLR on it. (SRAM support)
• Look at the drive-side dropout area. A Full Mount derailleur clamps around the frame there. (SRAM) Damage or bent parts in that area deserve a shop's opinion before you buy.

If it already has XPLR 13-speed fitted

• Confirm the cassette is an XPLR 13-speed cassette. The Full Mount derailleur works only with those. (SRAM)
• Confirm the chain is a road Flattop chain. (SRAM)
• Confirm the rear hub has an XDR driver body. (SRAM)
• Ask whether the derailleur has been removed and refitted. SRAM has a support article on reinstalling a Force XPLR AXS derailleur. Ask the seller if they followed it, or budget a shop setup.

If you plan to convert later

• Price the whole change, not just the derailleur: cassette, chain, and possibly a freehub body or wheels. We do not list prices because they change often.
• Check the crankset chainline against SRAM's chainstay guidance above.
• Keep the old UDH hanger. It is what you need if you go back to a hanger-mount derailleur.

Disclosure: Pedal Brief may earn a commission if you buy through links on this page, at no extra cost to you. This version has no affiliate links. We have not fitted these parts to these frames ourselves. Everything below comes from SRAM or the frame maker, linked where it appears. Full disclosures.