Check rear axle to swing arm pivot distance - both sides http://www.youtube.com/watch?v=4Dw2RZlUoUY No broken / bent / loose spokes? Rims in good condition? Wheels were trued? Tires not cupped? Tires / wheels balanced? Caliper aligned to the rotor? (not dragging) Wheel and swing arm bearings with out side play? Front forks straight? Fork internals and oil the same on both sides? Front forks in the triple trees the same distance per each side? Triple tree bearings adjusted? Fork brace in place? No loose fasteners? Use a string and tape to check alignment of the front and rear tires / wheels. Loop the string around the tires below the axles and fasten in place with tape. Look down the left edge - then the right edge. The string should look the same from side to side. Pulling a frame straight takes real effort with long pipes, wood shims, chains, extra people, trial and error, and real patience.