Are replaceable derailleur hangers outdated? Since SRAM launched its direct-mount mountain bike derailleur line in 2023, discussions have increased about whether this design will extend to road bikes, a vision realised in the recent Red XPLR.
Though the Red XPLR is part of its gravel bike series, it already demonstrates SRAM's ambition to set a new standard across its full range of derailleur products and industry.
What is SRAM UDH?
SRAM UDH aims to unify the derailleur hanger standardSRAM UDH aims to unify the derailleur hanger standard
SRAM states that integrating different hanger designs can make it easier to replace bent hangers and, with fewer variables, help optimise shifting. Like many other hangers, UDH consists of two parts: the hanger itself and what SRAM calls the "UDH screw," which secures the hanger to the dropout. On some frames, you'll need to use a "UDH frame spacer" between the hanger and the screw.
Some bicycles require the use of spacers
Additionally, you need to ensure the use of a compatible thru-axle to secure the rear wheel. SRAM specifies that the thru-axle must have an M12x1.0 thread pitch and a thread length of 12.7 mm. SRAM has made the design of UDH an open standard, meaning users are not limited to using only SRAM derailleurs; UDH is also compatible with other mountain bike groupset manufacturers like Shimano. Since the release of UDH, many brands have adopted this standard on their mountain bikes.
SRAM UDH and SRAM T-Type
The Eagle Transmission completely eliminates the derailleur hanger, mounting the derailleur directly onto the frame
In March 2023, SRAM launched its T-Type Eagle Transmission mountain bike drivetrain system.
While these new drivetrains do not relyr on SRAM UDH or other hangers, they lay the groundwork for future developments. The Eagle Transmission system is compatible only with bikes designed based on the SRAM UDH standard. Moreover, the system eliminates limit screws and B-screw adjustments on the rear derailleur.
The direct-mount derailleur installs directly onto the bike without the need for a hanger
Riders often complain about the introduction of new "standards," but UDH's promise mainly lies in enhanced durability, simplified replacements, and, most importantly, more accurate and reliable shifting. However, the high price tag (which may not be a flaw) and the inability to fit most existing bikes deter many. Due to the higher risk of derailleur hanger damage from crashes, UDH has been rapidly adopted by mountain bike manufacturers.
However, the adoption rate for road and gravel bikes is noticeably slower. With the launch of SRAM Red XPLR AXS (which uses direct-mount derailleurs), this may change, but I can already hear many asking, "If UDH is so great, why hasn’t every bike brand adopted it?" In fact, trying to get all bike brands to agree on a universal standard is like herding cats. The only thing bike brands seem to agree on is pedal threads—every now and then, some even try to reinvent the bottle cage. Notably, road cyclists typically fall less often than mountain bikers, although replaceable derailleur hangers are not without their drawbacks.
When SRAM first released the direct-mount derailleur, bloggers raised questions about it. While making better, more durable products is a constant goal in manufacturing, do current replaceable hangers have clear flaws from a user perspective? Is their sturdiness sufficient for mountain bikes? Do they need replacing?
Next, we will delve into the pros and cons of traditional replaceable hangers versus direct-mount hangers to explore whether it’s worth making the leap.
UDH and SRAM T-Type
Advantages
In the 1980s and early 90s, steel was king for "real" performance road bikes. Steel is known to be the ideal material for bike frames and derailleur hangers. Its "real feel" is always helpful, and it is sturdy enough to withstand certain impacts.
If the hanger part of your steel frame accidentally shifts out of place, it can usually be corrected with minor adjustments. In the worst-case scenario, steel can be repaired, and bent or broken hangers can be replaced.
With the advent of aluminium and carbon fibre, things became more complicated. Both aluminium and carbon are difficult to repair and costly, leading to the emergence of replaceable derailleur hangers.
These fragile little parts are designed to break during a fall to protect your expensive frame and derailleur.
The benefit of this design is that it introduces another component that requires installation, creating a degree of inconsistency that doesn't align with the modern driver's demand for precision.
In the early days of replaceable hangers, we faced 8-speed and 9-speed systems, while today’s 11-speed, 12-speed, or 13-speed systems have much lower tolerance for setup errors or hanger alignment issues.
No matter how expensive your frame or groupset is, no bike is immune to the annoyance of a bent derailleur hanger.
Even something as simple as a little extra paint on the interface can cause a replaceable hanger to misalign.
Worse, nearly every frame has its own unique derailleur hanger design. Like bottom brackets, there isn't a universal hanger that you can find at every bike shop.
I know many riders feel disappointed by the promise of a miraculous new "standard" that claims to solve all problems and provide endless good times, but UDH is not that. In reality, UDH is quite simple—it’s just a round hole on the drive-side dropout, not a whole new derailleur hanger.
Even the laziest frame manufacturers should be able to create a level axis on the rear of the frame without needing any unique parts or introducing dimensional differences.
Likewise, if you wish to use existing rear derailleurs (not all of which have direct-mount designs), you can still use threaded inserts with traditional hangers, like on the Santa Cruz Stigmata and eighth-generation Trek Madone SLR.
Disadvantages
UDH specifications also have some drawbacks. While SRAM claims its specs and T-Type derailleurs are sturdy, many riders worry that UDH might damage the frame, lacking the protective design that allows replaceable hangers to break first.
Essentially, part of the frame is now designed by SRAM instead of the frame manufacturers. Some manufacturers might welcome this as it alleviates some of their work, decision-making, and risks, but others might feel this limits their design freedom.
Moreover, UDH specifications require more clearance since the derailleur must be able to rotate backward. This isn’t necessarily a bad thing, but frame manufacturers must take this into account. The thru-axle interface is also preset, limiting axle choices and optimising rear-end rigidity. At the same time, you can't adjust chain length via flipping chips on the thru-axle, so manufacturers must seek other solutions, like the variant from Specialized. They must weigh the choice between adhering to SRAM's UDH specs or continuing with traditional hangers.
Traditional Replaceable Hangers
Advantages
Despite the variety of hanger specs available, common replaceable hangers are still easily obtainable and inexpensive.
From a manufacturing perspective, the downsides of direct-mount derailleurs are precisely the advantages of traditional replaceable hangers. Although the standards vary, traditional replaceable hangers can be installed in various ways, such as direct mounting or B-Link mounting, and do not interfere with the bike frame's design. Frame manufacturers can design frames according to their vision without worrying about compatibility issues, meaning consumers don’t have to consider derailleur compatibility too much when purchasing a frame.
Collision protection is an advantage of replaceable hangers. When the derailleur encounters an impact, the hanger usually breaks first, protecting the derailleur and frame.
Although direct-mount derailleurs promote their sturdiness and reliability, the risk of direct impact damaging the frame remains in the event of potential collisions.
Disadvantages
While using Shimano Deore and Sora derailleurs, I previously used SLX and Saint without encountering shifting issues after properly adjusting the derailleur. Therefore, the lack of smooth shifting with replaceable hanger derailleurs may stem from other factors, such as chain length, chain condition, and derailleur adjustment.
Thus, traditional replaceable hangers have some advantages but also carry drawbacks.
Conclusion
The discussion around "Do we need to eliminate replaceable hangers?" versus "Do we need to keep replaceable hangers?" ultimately boils down to a matter of choice. While SRAM's UDH system has advantages, it doesn’t mean it will suit every rider or every frame. Although I appreciate the concept of direct-mount derailleurs, replaceable hangers still hold unique value, especially in the realm of replaceable hangers.
Whether or not you are eager to embrace the new standard, it is important to use the right tools in the right situations.
Rather than pursuing a “perfect standard” for every situation, it’s better to allow riders the freedom to choose in different environments, ensuring it suits their riding style and needs.
