About CNC derailleur hangers

1. What is a derailleur hanger on a bike?

The main purpose of the replacement derailleur hanger of the bicycle, strange as it may sound, is to break at the right moment. This small structural element acts as a safety device when the load on the rear derailleur exceeds the allowable (bicycle fall, foreign objects hit the transmission elements, tightening the rear derailleur in the spokes of the wheel, etc.) taking the brunt of it. In order for the “rooster” on the bike to “correctly” break, its construction almost always provides for special weakening elements, stress concentrators, ledges, thinning, or holes. In addition, bicycle manufacturers, with rare exceptions, make derailleur hangers of light and brittle silumin (foundry aluminum alloy with a high content of silicon).

2. Why do we mill roosters from 2024 T4 duralumin?

It would seem, why reinvent the wheel. Everything works this way. Blow → break → replace and go again. However, it is not always the blow or when the bike falls, the derailleur hanger breaks immediately. With a relatively small load, it can bend a little, breaking only the correct operation of the transmission. There is a great temptation to simply fix the bracket and exploit it further. So in the case of regular silumin hangers, this editing cannot be done in any way. A bent derailleur hanger is also subject to mandatory replacement, as well as a broken one. Silumin alloy is not deformable, but foundry. In the case of deformation, internal stresses and cracks occur in it, which may not be visible to the naked eye. Thus, having corrected the silumin derailleur hanger, even if it did not break while editing, you get a time bomb near the rear wheel, which can “jerk” at any moment. The hanger can break even from simply rolling off the curb.

Our workshop mills derailleur hangers for a bicycle made of structural aluminum alloy 2024 T4. This is a “deformable” material that is rolled or pressed during production. This method of machining gives it special properties. Now it can take on significant cyclic deforming loads (repeated bends and shocks) without breaking. That is why 2024 alloys are used as structural materials in moving mechanisms, including aviation. Our CNC milled rear derailleur hanger will break down just like the silumin one in the event of a serious accident, since it also provides for stress concentrators and weakening elements. But if our “rooster” is just bent, it can be safely corrected by improvised means or a special tool and continue to operate the bike. We have a unique case in practice - 7 edits of our milled hanger on a road bike after repeated falls and blockages in races. Thus, the hanger milled from the alloy 2024T4 acquires new qualities that will prolong its life. In addition, the milled “rooster” is more rigid and resilient with lateral loads, which reduces vibrations in motion and improves the accuracy of the rear derailleur and the entire transmission of the bicycle.

Фрезерование велосипедных петухов

Milling the party of derailleur hanger #230 in the workshop Velofrezer

3. Design features of our derailleur hangers

We do not make exact copies of cast cocks for the bicycle, and we make the products of the best quality. Our hangers are manufactured using our own unique technology and include some design and technological changes based on many years of experience in the production and operation of bicycle rear derailleur hangers in various conditions. These innovations significantly improve the properties of the bracket in comparison with regular products:

  • A special gap between the outline of the frame's dropout and the thickened part of the “rooster”, which excludes the “lever effect”, crushing the frame material when the hanger breaks.
  • The lack of sharp edges, cutting off the frame material in case of significant deformation of the bracket - milled chamfers are provided around the perimeter of the “bike rooster”.
  • Lead of threading height in holes (minimum number of threads) to the requirements of ISO and GOST.
  • The elimination of some other technological features required in the manufacture of parts by casting from soft alloys, but unnecessary and even harmful when milling products from wrought alloys.

Due to the changes made, our “cycling roosters” have less weight with greater rigidity (resistance to bending). And in the event of an accident, they are destroyed (play the role of a fuse) at points without critical contact with the bicycle frame.

Правильно сломавшийся велосипедный петух

A properly made bicycle rooster breaks without damaging the frame and retaining the rear derailleur. Derailleur hanger #195 of our production after an accident in the race.


Considering that a rear derailleur hanger can break at any time (including far from home or a workshop) you should always have a spare "rooster" for your frame or a universal hanger suitable for most bicycle frames in your bike kit. Therefore, in our workshop, when purchasing 2 or more derailleur hangers, there is a 10% discount on the order value (the discount is charged automatically when placing an order in the cart).
Workshop "Velofrezer"