Bolt through axles -why ?

[GrumpyGregry]

I find it very hard to believe that the amount of flex in a traditional qr, which must surely be minimal, would result in the tyre rubbing the forks. If this is such a problem how come it doesn't happen on the road ?

I can get the rims on my touring wheels to rub the calliper brake blocks when "honking". My old fixed did the same. DH MTB, fat tire and a large fork stanchion with not much clearance between the two could I think result in tyre fork contract under duress. But the flex ain't coming just from the QR.

 

[GrumpyGregry]

I'll ask Chris Juden what his thoughts are on it and report back.

You should ask the people at SJS, they can rant about it for hours.

 

[swansonj]

(I vaguely remember reading that a hollow axle will be stronger than a solid one because of SCIENCE)

I vaguely remember that the difference isn't so much in it being hollow per se - the material missing is at the centre where it makes only a small contribution to strength. But in a hollow axle with a skewer through it, the axle is in compression, whereas with a solid axle bolted at the ends, it's not. When subjected to forces - like the weight of the rider - there is a bending moment on the axle. With the solid axle, that results in compressive forces on one side but tension on the other side (think bending a wooden ruler). If it's going to fail, it will fail as a result of that tension (think bending a ruler again). With the QR axle, already in compression, the bending moment increases the compression on one side and reduces the compression on the other side, but it never actually goes into tension anywhere. That's why it's stronger.

 

[andrew_s]

My understanding is that through axles happened to help keep the sliding lower leg sections on suspension forks properly aligned. With rigid forks any tyre rub will be due to a combination of poorly adjusted cup & cone bearings and slack spokes rather than to axle flex.

Wheel ejection due to disc brakes does happen. In the case that happened right in front of me, it was an allen key skewer on fresh paint with no lawyer lips, the wheel had never been out of the (new) bike since collection from the maker, and every other bolt on the bike was done up gorilla tight.
Even if a QR is done up properly to start with, if you use a boutique QR with a weak grip it can loosen off in use. There are occasional forum posts asking why the top of the wheel moves sideways under braking.

 

[GrumpyGregry]

My understanding is that through axles happened to help keep the sliding lower leg sections on suspension forks properly aligned. With rigid forks any tyre rub will be due to a combination of poorly adjusted cup & cone bearings and slack spokes rather than to axle flex.

Wheel ejection due to disc brakes does happen. In the case that happened right in front of me, it was an allen key skewer on fresh paint with no lawyer lips, the wheel had never been out of the (new) bike since collection from the maker, and every other bolt on the bike was done up gorilla tight.
Even if a QR is done up properly to start with, if you use a boutique QR with a weak grip it can loosen off in use. There are occasional forum posts asking why the top of the wheel moves sideways under braking.

There's your answer.