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On opening the cam lever of a 15mm through-axle, I have noticed it is possible to slide the axle out after only two whole turns. When installing the axle, more that two turns results in a cam tension that is too tight, less than two turns then the cam tension is too loose. I am concerned about safety and durability.

Does anyone know the minimum turns that a through axle should have in order to retain the wheel? Otherwise what is the typical number of turns from your experience? The bike in question is a cyclocross (if that makes any difference).

The image shows the threaded hole from the inside of the fork. enter image description here The length of the bolt that goes into this whole matches the outside distance of the fork, however the bolt is tapered at the end so the thread at the very end is not used. The partially threaded hole seems to by typical of thru-axle designs to allow the bolt to pass into the fork for alignment purposes before threading begins. In this case however I believe there is insufficient thread.

This is a new bike and I have concerns over safety and long term durability.

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    Sounds way too little. I know a bolt should have 6 full turns minimum for engagement, but over half of the load is taken by one-two turns of thread material. Can you see any of the bare thread still, either on the Axle, or inside the hole on the fork?
    – Criggie ♦
    Oct 23, 2016 at 19:04
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    A bit of research on the web provides the following rules of thumb for minimum thread engagement for a steel bolt: it should be equal to a distance as the same diameter as the bolt, or at least 5-6 turns. I know this is a hollow bolt, so it might not be the same. However the fork t thread is aluminium, and the commencement of the thread will be graded-in, to in reality, it is not even two full turns of proper thread.
    – Antony
    Oct 24, 2016 at 17:15
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    Simply looks like a manufacturing error. The thread hasn't been cut completely through the hole. I'd take it back to the shop you got it or contact the company.
    – DWGKNZ
    Oct 24, 2016 at 18:43
  • I double checked one at work. It looked similar to the picture, probably the same maker but not necessarily, and possibly with a few more threads. It did have the plain unthreaded part, and had 4.5 turns of engagement.
    – Nathan Knutson
    Oct 25, 2016 at 17:23
  • To all commenters, remember that the axle is operating in shear, not tension. The threads are really just there to keep it in place. Since OP is mentioning cam tension, they have a TA that has a expansion wedge for even more retention power. Although undoubtedly sketchy, as long as you've never experienced the axle loosening on its own, you will be fine. If anything, you'll have faster wheel changes in a race :)
    – MaplePanda
    Jan 9, 2021 at 5:26

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Sounds weird and wrong. Usually you indeed have a lot more thread engagement, I think 5-6 turns or more on the road/cross forks I have my hands on all the time. If there are a lot of threads present on the fork and nothing filling them up, I agree it sounds unsafe.

One easy possibility is that the bike ended up with an axle that isn't a correct match for its fork, and someone either didn't notice or care. To be really right it must be the axle intended to go with the fork in question, and they can require some work to track down, particularly if it's an OEM fork as opposed to a named aftermarket one.

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    Agreed. I have though that a slightly longer bolt would make use of all the thread in the fork but it looks from the photo i would only get about 4 to 5 turns maximum. This is 15mm thru-axle of unknown manufacturer. Anyhow this is a new bike and am considering my options.
    – Antony
    Oct 24, 2016 at 17:19

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