Um bud, THe size difference in the tires will do that. If you are checking to see if you are aligned run a string down both sides and measure the distances from the tires. For example run two strings parallel to each other at 8" apart. Center the bike in between them. Now measure the distance to the tires. Depending on the offset of your tires from the factory they should be the same. Now in some cases they will not ie: my Honda has I believe 3/16 or 1/8 difference in the rear from the front as to where center is. This is not uncommon among manufacurers.