Someone more knowledgeable than me should answer this, but here is the information provided me by a dealer:
Trad wings (except new plus8) are produced from the same mold, and are cut from the "inside" to suit the body/axle width. The position of the headlights are always the same when measured from the "outside" of the wings and inwards, as well as the space inside for wheels. There may be mechanical limitations to wheel width other than "wing width".
The "tub" is the same for all.
For cars up to 2011 I believe there where tree car widths:
4/4 narrow width
Plus4 medium width
Plus4 Sport widest
Roadster widest
From 2012:
4/4 narrow width
All others widest
Last edited by normog; 15/04/12 06:08 PM.