Anybody know how to determine if a disc is warped using the average man's tools / resources? I've only had the GT on the road for a month, and it had a new front disc fitted to the twin-disc front for the RWC, but when I brake and get to the slower end of my speed, not only does the handle pulsate, but I get this rocking back and forth, as though the disc were warped (the rocking is of a rhythm that would equate to one full turn of the wheel, I suspect). It's quite prominent. Alternatively, I'm figuring there might be an air bubble in there, as the discs *look* fine (when lining them up by sight), and so I'll also bleed the brakes, but I'd like to know how to check the disc as well. Could there be any other cause? THe disk are certainly tight and otherwise moving.