Own 2011 Boxster 2.9 PDK Gen 2 987 running Cayman 18" 235 front 265 rear tyres and been recommended to get standard size wheels with tyres all round including winter tyres .. Do all Boxster wheels fit - I see adverts not specify other than 986 / 987? how do I know what size offset they should be? I thought standard size if 17" but see tyre widths 205 front and 235 rear. I am only interested in genuine wheels.