is the TIRE fully beaded onto the rim? are you certain the headset is not too tight? is the frame's steering head angle just too steep from the factory? is the rim centered to the fork, and has the wheel's "center" been checked with a centering gauge? is the fork the stock, original one? A shorter than correct fork will steepen the steering angle... the Longer top tube was designed to stabilize the bike, and i;d be suspect that was done to possibly CORRECT/cover up a chance of wobble from a too-steep steering angle... Is the frame possibly TWISTED from an accident, or improper jigging at the factory?

i've seen more than one conti tire with not-good case/tread alignment from the factory, btw... and they tend to run tight on their bead diameters, making full beading tough, if not impossible, on somewhat larger rims... YES, there are variances in rim diameters within 700c rims from various sources, or any other class of rim sizes.......