4

Most bolts on bikes are using hex sockets. However, there is at least one exception: the 6 bolts of brake discs, which usually have Torx sockets.

What is the reason for this? Has the Torx socket a significant importance in this area in particular?

Related question: I'm considering replacing these bolts with titanium version (saves 6 grams per wheel, woohoo!), and I can buy them with either hex or Torx sockets (hex would be a bit more convenient as I have hex keys readily available everywhere, on the other hand, the Torx socket is technically better). Can I just pick the socket I prefer, or would you strongly advise for Torx?

  • Refs this related question I just found out: Is there anything special about rotor bolts? – Gras Double May 9 at 3:33
  • There may be warranty and liability issues because the brake was designed like that and it is a safety relevant item. – Carel May 9 at 7:25
  • That related question was me. I haven't had any issues with my stainless socket hex head bolts (though I have had other brake trouble). I've also never needed to remove or tighten a rotor on the road and I have plenty of Torx tools at home – Chris H May 9 at 13:53
  • Because everyone already has Allen keys. – Brian Drummond May 9 at 19:23
10

The magic of lobes allows Torx to handle a given torque value with a shorter bolt head than the alternatives, and some frame/fork designs need the clearance in this area. That's the only reason for it.

Some secondary bolt retention designs won't work with just any bolts, ie Shimano.

| improve this answer | |
  • Could we say that, basically, the Torx socket is here to help preventing the key from ripping off because of the small button heads? – Gras Double May 10 at 1:38
  • 2
    Yes. Or in other words, the M5 Allen option for a similarly low-profile bolt head would be a button head screw with a 3mm Allen fitting. That would be borderline for the ~6Nm torque needed. – Nathan Knutson May 10 at 1:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.