Sorry I think the differece is about 2-3mm(not 5-6mm). Actually this is just my assumption but I'm sure the difference exists. Also I agree with you to say that unbalance could result from other elements like saddle tilt and other things. I didn't know that there are bikes which have the unbalanced rear center. Could somebody let me know which difference is acceptable for fine ride? I think that will help when buying new bike someday. Lesson learned anyway..