Anyone handy with offset calculations?

[Snorkel]

Looking at replacing my standard alloys on the 5.5 for some 18's.

Not sure what the standard alloys specs are but presumably someone on here knows?

Wheels I'm looking at are:

Front - 18x8.5 ET30
Rear - 18x10 ET25

Does anyone know if these are appropriate dimensions for a 5.5, and what sort of tyre sizes should I be looking at?

Cheeeeeeers!