I have been working on switching over from my XT V-Brakes to a set of BB7's on the front (right now the rear will follow). After a little bit of tinkering I got the calipers installed and adjusted, took it for a little test spin and everything was great, the pads seemed a little sticky (partially because they were new, partially because I pulled them too hard initially and partially because I didn't have enough air in the new shock and the nose dove) but I was excited to have the new brakes on. The first time I rode them everything was perfect, no issues whatsoever. The second time riding the trails I noticed that when I turned sharply the disc would rub a bit, I think this can be attributed to a little bit of flex in the wheel since I am not exactly a light weight... again this was acceptable. However on my way home from the trail on the road we started picking up a little more speed and the disc really sounded like it was starting to drag. If I quickly squoze the brake lever the sound would go away for 20-30 seconds but then would come back. When I got home I started from scratch and completely refitted the brake, when I spin the wheel on the bike there is no sound at all, but after another pavement test ride once I get moving pretty quick the rotor sounds like it is scraping the pads again, but only when I am going quickly... ( I don't have a computer on my Mountain bike so I don't know the exact speed but I would think it's right around 15-16 mph.) Any ideas on what would cause this at higher speeds (and a straight line) but not lower speeds?
It's caused by lateral flex in the front fork. 185's and 203's are more susceptible to it since they're further from the axle centerline. I have a Gary Fisher that does the same thing. You can sometimes back the pads off a touch more to help eliminate it but didn't totally alleviate it on mine.