Originally Posted by
dabac
Thru-axle assemblies are rather stupidly designed, since there is nothing providing an actual definite position of the parts. The axle has to be a loose fit in the hub to allow easy, hands-only installation. So the rider end up having to rely on the end caps of the hub being pinched between two parallel surfaces as the sole mechanism keeping the wheel positioned.
What happens is that applying the brake causes a downward force on the axle, and riding causes an upward force on the axle. In the absence of a definite centering feature, a TA that hasn’t been closed with sufficient force will allow the wheel to move (ever so little) up & down, as dictated by how loosely the axle fits in the hub.
One trick that might help is to tighten the TA with the wheel off the ground. That way, the slack is taken out and the wheel is already resting against a definite reference.
Brake forces can’t move it any further, and w/o jostling, there’s far less going on that can cause the axle to unscrew.
Another trick is to just tighten the TA properly and not have any issues. It ain’t rocket science.
I think it is a stretch to call the TA a stupid design due to what happens if it is not properly tightened. It is a whole heck of a lot better than what happens when you don’t tighten a 9mm QR.
The reality out on the road and trail is that TAs do a perfectly good job of keeping the hub exactly where it needs to be, and are actually better than QR at getting disc calipers and rotors to consistently line up after wheel changes.