i have an 06 yz450f and an 04 zx10r. I tightened up the chain on both bikes the other day. I noticed if i turned the wheel over 180 degrees the chain would get tight then loosen again when i turn it back. It does this on both bikes so i don't think it is not lined up correctly. Any one know why this happens? Seems like the lenght of the chain would stay the same since the tire and sprockets are round.