Universal Derailleur Hanger (UDH)

Summary

The Universal Derailleur Hanger (UDH) is a standardized derailleur mounting interface introduced by SRAM to simplify rear derailleur hanger compatibility across frame brands. It reduces the complexity of sourcing replacements and forms the foundation for SRAM’s direct-mount Transmission drivetrains.

Key Facts

  • Introduced: 2019
  • Category: Component
  • Also known as: UDH
  • Used by / Found on: Modern mountain bikes (and expanding into gravel, e-MTB)
  • Rear dropout interface: Standardized hanger mounting and rear axle contact
  • Supported by: SRAM, Trek, Transition, Specialized, Ibis, Yeti, and others
  • Supports SRAM Transmission direct-mount systems
  • Official site: https://www.sram.com/en/sram/mountain/collections/udh

Overview

Derailleur hangers have long been one of the most frustratingly inconsistent components in the bicycle world. Each bike brand — and often each frame model — had its own hanger shape, bolt interface, and dropout design. This led to a confusing ecosystem with hundreds of proprietary hangers and frequent compatibility headaches.

The Universal Derailleur Hanger (UDH) was introduced by SRAM in 2019 as a solution to this chaos. Rather than continuing the fragmented status quo, UDH establishes a single shared mounting standard for rear derailleur hangers, intended to work across multiple brands, frame types, and suspension designs.

UDH was designed to do three things:

  1. Standardize the mounting interface so a rider or shop can easily find a replacement hanger.
  2. Protect the derailleur and dropout with a carefully tuned failure mode.
  3. Enable future drivetrain innovations — including SRAM’s hangerless, direct-mount Transmission systems (like XX SL, XX, XO).

Importantly, UDH doesn’t require bikes to run SRAM drivetrains — many UDH-equipped bikes use Shimano or other brands. But the interface ensures universal fitment, easier manufacturing for brands, and a cleaner future-proof standard.

Since its release, UDH has rapidly gained traction among major brands, with many new mountain bikes now shipping with the interface by default.

How It Works

UDH consists of two parts: the hanger itself, and the dropout interface it attaches to.

The Hanger

The UDH hanger is made from aluminum and designed to flex or break away during an impact — like all traditional hangers — to protect the derailleur and frame. However, it’s specifically shaped to work with the UDH interface, which includes:

  • A rear-facing T-shaped slot
  • A 12 mm thru-axle that passes through the derailleur, hanger, and dropout
  • A locating boss on the hanger that slots into the frame recess
  • A small retention bolt that keeps it centered when the axle is removed

This design ensures precise alignment of the derailleur while enabling the hanger to rotate backward slightly during a direct impact — a feature designed to protect drivetrains from rock strikes and trail abuse.

Rear Derailleur Mounting

For standard mechanical or electronic derailleurs (e.g., Shimano XT, SRAM GX, etc.), the UDH acts like any other hanger. It mounts the derailleur at the correct B-knuckle location and uses the axle to tie the system together.

However, with SRAM Transmission drivetrains (introduced in 2023), UDH opens the door to a new architecture: the direct-mount rear derailleur. In this setup:

  • The derailleur mounts directly to the frame’s UDH interface.
  • No hanger is used at all.
  • The interface becomes structural — allowing for increased stiffness, tighter tolerances, and shifting under full load.

This is a significant shift in drivetrain design — one that requires the bike to have UDH baked into its geometry and frame structure.

Compatibility & Transmission Integration

Mechanical Drivetrains

UDH is fully compatible with:

  • Shimano mechanical and Di2 derailleurs
  • Older SRAM mechanical derailleurs
  • TRP, Box, and other aftermarket brands

It acts as a drop-in replacement for the previous hanger, provided the frame supports the UDH interface.

Riders benefit from:

  • Easy access to replacements (any shop with UDH stock can help)
  • Consistent derailleur alignment across bikes
  • A single spare part that works across multiple models and brands

SRAM Transmission (T-Type)

SRAM’s new Transmission drivetrains — including XX SL, XX, XO and GX Transmission — require a UDH-compatible frame, because the derailleur mounts directly to the frame.

These systems eliminate the hanger entirely and use a hangerless interface to secure the derailleur to the dropout and axle. This architecture:

  • Improves shift accuracy and stiffness
  • Enables “shifting under load” with full power
  • Prevents misalignment due to hanger flex or bending
  • Requires tight tolerances between the frame and derailleur mount

If your frame isn’t UDH-compatible, Transmission cannot be used — at least not in its intended form.

Gravel & E-MTB

UDH has started to appear on high-end gravel frames, particularly those expected to run wide-range MTB-style drivetrains. It’s also a natural fit for eMTBs, where motor torque and shifting force benefit from the stiffness and protection of the UDH interface.

Brands including Specialized, Yeti, Trek, Pivot, and Ibis have rolled out UDH in eMTB platforms, knowing it offers both immediate replacement ease and future upgrade paths.

Notable Implementations

  • Trek Fuel EX and Slash (2020+) — Early adopters of UDH, offering Transmission compatibility
  • Specialized Levo and Stumpjumper EVO — Switched to UDH for 2021+ models
  • Santa Cruz Megatower, Nomad, Tallboy — UDH added for compatibility with future SRAM ecosystems
  • Transition Patrol and Spur — Updated dropout designs with UDH standard
  • Pivot Switchblade and Trail 429 — Designed around UDH for drivetrain compatibility
  • Yeti SB160 and SB140 — Built with Transmission and UDH in mind

Related Terms

  • Derailleur Hanger
  • SRAM Transmission
  • Direct-Mount Derailleur
  • Thru-Axle
  • Frame Compatibility

References

  • SRAM UDH Technical Documents and White Paper
  • SRAM Transmission Compatibility Charts
  • Pinkbike: “What Is UDH and Why It Matters”
  • BikeRadar UDH Frame Compatibility Guide
  • Manufacturer frame specs: Trek, Santa Cruz, Pivot, Specialized
  • SRAM Dealer Service Manuals
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