What is UDH?
SRAM’s Universal Derailleur Hanger, or UDH was introduced in 2019 to standardize derailleur hangers. Bike frames that are compatible with UDH are also compatible with SRAM’s direct mount derailleur design, Transmission, and vice versa.
UDH attaches to the drive-side dropout of the frame using a bolt with a 20mm head, called the “UDH Bolt”.
This bolt may have information etched on it that will help you identify if it is part of a UDH hanger.
If you are unsure, most manufacturers will mention if a bike is UDH compatible under the component specifications for your bike. Any bike that comes equipped with Transmission is UDH-compatible. Please reach out to your bike's manufacturer if you need help finding this information.
Why is UDH important when choosing an axle?
Bike companies have widely adopted the UDH standard on their frames. Often, the introduction of UDH on a frame will change in the axle’s length and/or thread pitch. This change does not always coincide with the change of a model year or the release of a new model, so for some bikes, our Axle Finder will ask you if your bike has UDH or not.
It is essential to match the thread pitch your frame is designed for with the thread pitch of your OMM Fit Kit Thru Axle. Failure to do so can result in damage to your bike and may void your manufacturer's warranty.
Bike model variations that include UDH-compatability have been updated in our Fit Kit Finder tool to be designated clearly as the UDH variant.
For example, the Esker Hayduke with UDH is called, "Hayduke UDH" whereas the non-UDH version is simply listed as "Hayduke."
When you are working with our Axle Finder, please be sure to review all available options to ensure you are selecting the correct axle for your bike.
Will UDH get in the way of Fit Kit axles?
Nope!
Fit Kit axles are the best way to attach a rack to your UDH-equipped frame. Our drive side axle end fits through the 8mm broach of the fixing bolt and threads into the shaft of the Fit Kit axle.
You do not have to modify or adjust your derailleur or shifter in any way to use an Old Man Mountain Fit Kit thru-axle. Our Fit Kit thru-axles preserve the quality of your shifting while attaching our racks to one of the strongest points on your bike.
We make sure to account for the extra width that UDH and Transmission add to a frame when recommending our axles.
Just enter your bike information in our Fit Kit Finder and you are good to go!
Tips and Tricks
- UDH and Transmission dropouts are designed to accept axles with M12 x 1.0 thread.
- A great upgrade for any UDH compatible bike is the Robert Axle Project Universal Derailleur Hanger. Installing this all-metal precision machined hanger in conjunction with our high quality axles is a great way to firm up the rear axle interface of your bike – this often improves shifting accuracy and braking performance over the stock axle/hanger!
- If all else fails, please reach out to us via email or our Contact Us form. We are here to help you!