Some tyre manufacturers come up wider than others for the same size, just depends on the design... you can fit wider tyres on the Aero.. the measurements can be found on the net somewhere...

You'll need the Rim width from OZ then cross reference against the tyres you wish to use to see if that width can be used. These are published in tables on the tyre manufacturer's web-site.

I think you can fit upto 18' 245's on the OZ rims if you use the Yokohama A048's but go too wide and you end up needing to shave the wheelarch.

Which ever route you take always follow the tyre and wheel manufacturer guidelines. (I know that's a bit obvious, but worth saying anyhow.)