I am waiting to hear back from biketiresdirect on this, but it's weird: I mounted both tires (Schwalbe Winter Marathons) and gave 'em a spin, and they wobble, side to side, up and down. Not a lot, but enough to make me wonder if I got a bum set. I deflated them and checked the tubes; no problem there. Is this normal or should I make them do an exchange?