Originally Posted by
elemental
I knew this was an issue with discs, but I have yet to find good evidence that increased rotor size increases the forces involved.
EDIT: Previously I wrote here something that, at better inspection (had a shower and made a static diagram in my head) turned out to be false.
So: the forces acting on the fork exerted by the axle are the same, regardless of the radius of the rotor.
The problem is in the curvature of the circumference, which in the case of a larger rotor, is longer, and potentially increases the likelihood of the axle dropping out from the dropouts.