The disks are meant to have no run out (wobble). But real life isn't so nice. As long as the actual run out isn't so much that the disk rubs on the pads then all is still well. But the width between disk pads varies due to caliper design, pad wear and quality of piston manufacturing (many pads mount off square on low end calipers, turn the fixed one in or out and watch the pad "orbit" a bit). So the actual allowable run out also varies. For small run outs that are not too "tight" a truing fork works well with some practice. Andy.