Hubcentric Rings

[Burnes]

How can I find out the outer diameter of my aftermarket wheels?
Where can I find out on the internet?

Thanks.

[Tobeit]

Call the shop you bought them from. If your shop does not know, look if someone like tirerack, discounttiredirect etc have the same brand and call their tech support.
.....or simply measure it.

[touringcamry]

You could get a set of calipers and measure it.