Wow, you know you're fast when you manage to outrun your rear wheel . I've had wheels shift position on me before but I've never had one make it past the brake pads and out of the dropouts. Usually when it happens to me it's because I wasn't paying attention to protruding axle length vs. dropout thickness but, y'know, axles don't really grow spontaneously so I can't really offer any ideas. I can, however, make some cracks about build quality of French bikes if you'd like .