Hi what are the standard chrome rims like ?

Is it worth changing to an 18 " Rear for better tyre choice ?

any advice Cheers

The standard rims are strong, best thing to say about them. The quality of the chrome is crap, they rust.

Opinion seems devided about 18" rims for the rear. Tyre choice is good enough in europe, are you going somewhere where that may not be the case? 18" used to be mandatory for Africa, but that seems to be changing.