How the system works... The important parts in the system are the hub axle with serrated locknuts, the quick release skewer with serrations on the faces of the skewer, and the fork dropouts. The serrations on the axle dig into the inside faces of the dropouts. They are harder than the dropout material, so they cut grooves for themselves. This prevents movement of the axle, either up or down. Forks are springy, and the grooves cut by the locknuts are quite shallow, so without help the serrations will slide out of their grooves. So the quick release skewer pulls the two dropouts hard onto the axle. The skewer is only in tension - there is no shear force at all on the skewer. Under static conditions, this is all that would be needed. But in the real world, a bicycle is subjected to a lot of vibration - a simple skewer would quickly loosen up. So the skewer has serrations which also bite into the dropouts, to stop it unscrewing. These serrations are only resisting the vibration - they have nothing directly to do with holding the wheel in. So is James Annan’s theory correct? The following is my opinion... His initial analysis is correct, the force diagrams and calculations he details are accurate, and as someone with a degree in Physics, I have no problem with that part of his theory. I am less sure about the consequences of the basic maths. These are my reservations: In Annan’s analysis, the two forks legs are assumed to be independent - the force from the disc brake is assumed to only act on the left dropout. I do not believe that this is correct in practice. Imagine what happens if the axle starts to come out on one side only. First, the disc rotor will have to be deflected - this requires quite a bit of force. Then the skewer will also need to be stretched by an amount proportional to the displacement of the axle. Thirdly, the axle cannot move far before the rim of the wheel contacts the inside of the fork leg - in most case I tested, it is not possible to remove the axle on the left side only.
So, basically, the force generated must be enough to overcome the strength of the serrations on both sides of the fork, not just the left side. The lack of documented cases. I have talked to a number of technical people at various manufacturers, and they have never seen this problem with their products. Yes, they could be covering up - but these were off-the-record discussions with non-lawyers so I do not think so.
The only recorded case was Annan’s own. This occurred with a custom-made tandem on it’s first outing. The rider weight of a tandem is double that of a solo bike, and the maximum braking force is more than doubled (it is harder to lift the back wheel). The forks in question were rigid steel forks of a particularly thin construction - forks I would not use on a tandem without a disc brake, let alone with. But all this is theoretical. I believe that there is a possibility of a problem with some combinations of components. Unlike James Annan, I do not believe that there is a fatal design flaw with all combinations of disc brake, fork and quick release. Go to the Experiment page for details of the practical tests I performed. | 
