Originally Posted by
nfmisso
A slight tangent: hollow vs solid: there is very little difference in strength of a tube (hollow) vs a solid. The bending strength of a solid axle is proportional to the diameter raised to the fourth power and inversely proportional to the length. For a hollow axle it is the outer diameter raised to the fourth power minus the inner diameter raise to the fourth power.
Lets look at some numbers:
10mm solid axle, the strength is proportional to 10^4 = 10,000
10mm axle with a 5mm hole through it: 10^4 - 5^4 = 9375
less than 7% difference, which is easily made up be a slight alloy or heat treat change.
Woohoo! Numbers!
And for what it's worth: back when I was a bike mechanic (Jurassic period? Cretaceous? So long ago...) I saw many, many broken solid axles. Those were on Schwinn Varsities, so they weren't great material and the bikes were usually abused, so it wasn't uncommon to replace a couple every week. Bikes with QR axles were not as common and treated better, so we didn't replace as many.