I know some people whos dattos are with a group called VGL and as long as the car is engineered if it has mods they are fine and the prices are reasonable.

One thing I would like to point out for wheel sizes is, like what has been said 2in bigger in diameter and 1 in wider.
But if you have up graded your brakes and its engineered, if you now have stanza brakes this is what the sizing now goes off.
I think that stanzas come with 13 as standard ( might be 14's) but now you can leagally put 15's and as long as the engineer is happy with the brake upgrade this size will pass.
The engineer can even approve bigger if he finds it to be satisfactory.