I'm looking at some vauxhall cavalier alloys, and the pcd is 4x100 so fine but the centre bore is 56.5 whereas polo's are 57.0. I know that you can get spigot rings when the bore is larger but what, if anything, can you do when its smaller than a polo?

Do you just get them machined larger at an alloy refurb shop??

machine reore, bout 20-40 a corner

The offset will be quite high as well if its a Vauxhall.