Rear wheel alignment

[andyb]

So how good are the marks on the swingarm for alignment, and is there a better way?

[NBs996]

Assuming the sprocket's on straight, what I do is get a flat rod of some sort and put it flat against the sprocket under the chain. If the rod lines up with the chain then the wheel's straight.
I think you can buy a tool that's designed for the same thing but haven't a clue where from!