I just purchased a Yuba Spicy Curry Bosch cargo bike with disk brakes and quick release skewers on both wheels. I haven't had any issues with it so far, in fact, I love riding it, but I have read that using disc brakes with a quick release axle can be dangerous, as the braking force can cause the quick release to loosen and the wheel to fall out. It seems crazy to me. Nobody wants to lose their front wheel riding.

Is the risk overstated? Is it something that only happens with badly designed or improperly adjusted QR/disc setups? I check brakes and tire pressure before every time riding, if I just check the QR as well am I going to be fine?

Would it be safer to just replace the quick release on this particular bike with regular nuts?

I just can't imagine it is a common occurrence, but since I ride this bike with my kid as passenger and share it with my wife, I really don't want to leave it to chance. I am curious to hear from anyone familiar with this particular problem of disc brakes, beyond what is stated in the Sheldon Brown article. Thanks!

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    The skewers are actually the thing you should be checking youtube.com/watch?v=qjOfPzWB2_U Not sure if discs can do anything to them though. I thing it is mainly just annoying to have not the disc brakes aligned perfectly due to imperfect skewer alignment or due to not enough stiffness. – Vladimir F Sep 12 at 16:59
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    If the QRs are closed in the correct and intended way, they are as secure as through-axles. Just teach yourself to do it properly. youtube.com/watch?v=Hcq-PwYj3TE – Carel Sep 12 at 17:51

The real problem with quick release skewers on a disc brake bike is that all skewers are not created equally, and some cheaper skewers distributed on QR disc brake bikes were not up for the task (hence recalls).

If you are using rim brakes basically any functional skewer will work, however as pointed out in the linked posts skewers on a disk brake front wheels will experience additional forces associated with braking being applied at the hub, rather than out at the rim (where you have much more favourable leverages and therefore less force required).

If you have a cheap skewer that does not produce sufficient clamping force, then you can get issues. For example, under heavy braking the quick release skewer and wheel may shift in the front drop out. This is usually pretty noticeable (i.e., sudden rotor rubbing or the wheel no longer sitting centered) and could potentially lead to loosening of the skewer over time if material begins to be rubbed away with a back and forth shifting.

This is however easy to test for. Set the front wheel QR as you typically do, take some measurements (visually is often all you need) so you can assess whether any movement occurs, then go for a short ride and try some aggressive stops with the front brake (make sure you know the body positioning for aggressive stops). If your front wheel shifts, then the skewer is supplying an insufficient clamping force for the braking application.

When in doubt internal cam skewers such as Shimano skewers tend to produce the most clamping forces. Whenever I have had issues with a front wheel shifting in the drop out of a QR disc bike, switching to a high quality Shimano Skewer has solved it.

Of course, the industry now provides thru-axle as another mounting option which eliminates this potential issue by directly bolting the axle to the frame. But Quick release can still be used safely given that you take the necessary steps to ensure you have a skewer that can produce the required clamping forces for your braking application.

  • I'd emphasize that internal cam skewers are better because they will produce more clamping force than external cam for the same amount of force that you apply to the lever. We can't see the QRs equipped on the OP's bike, but chances are that they're external cam ones. Those are more common and frequently cheaper than internal cam ones. That said, Shimano do make good and inexpensive internal cam skewers. Some info here; Sheldon Brown's site uses enclosed vs exposed cam, but internal and external seem the more common term. ncbi.nlm.nih.gov/pubmed/26132680 – Weiwen Ng Sep 12 at 21:04
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    +1: The lawyer lugs on most forks these days will prevent the wheel coming off even if it does become very loose. Because of this, the risk of the wheel falling off is overstated. If the OP's bike has lawyer lugs, I would not rush out and buy new QR's unless the axle is moving. (Done up properly this this highly unlikely, even with cheap external cam skewers.) – mattnz Sep 12 at 22:03
  • I think they are external cam judging by photos of different quick release. They seem fine, though the rear is harder to keep an eye on. They have large rotors, which if I understand correctly helps to reduce the downward force. It pays to pay attention to ones bike in any case! Thanks for the facts and insights. – SamArcher Sep 12 at 23:54
  • The rear wheel is less likely to be forced out of the drop-out, mainly because there is much more weight on that axle. And even more so on a cargo bike. – Carel Sep 13 at 6:58
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    @Carel: If the brake caliper is mounted inside the seat/chainstay triangle it should actually push the rear wheel upwards during braking (and the caliper downwards). In any case braking forces on the rear wheel are usually much smaller than on the front wheel. – Michael Sep 13 at 8:05

There was a huge recall of quick release bikes from Trek in 2015 (about 1000000 units in US and Canada). The reason was that the lever could, according open far enough to catch in a disk brake rotor. That could lead and in several cases did lead to serious injuries.

This particular means of failure ca be mitigated by having the lever on the drive side (opposite to the disc).

Loosening of a quick release by disc brakes is described by James Annan. I quote:

There are two main aspects to the failure.

The disk brake generates a massive force largely downwards in the direction of the open fork ends. The friction of a quick release skewer is often not sufficient to stop the axle slipping down in the dropout slot. This is explained in more detail here,

The QR is initially restrained by the retention lip on the fork (assuming it is present), however over time the slipping of the quick release leads it to unscrew, which is described here. Once it has unscrewed enough, it can be forced over the retention lip and the rider will crash.

Modern disc brake bikes tend to be sold with thru axles instead of quick releases.

  • Sheldon Brown passed away in 2008, how did he comment on a 2015 Trek recall? – lanzz Sep 12 at 20:37
  • @Ianzz The maintainers of the site did. But if you mind that source as untrustful, I can replace it... – Vladimir F Sep 12 at 22:14
  • It makes sense that bikes with disc brakes would also be thru axle rather than dropout. It further complicate things, but if you already chose to complicate things with hydraulic disc, why not accept that for safety sake? – SamArcher Sep 12 at 23:57

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