another wheel question just a quick one honest :-)

[mak]

Ok i no this is gonna bore people and maybe even annoy people but i just need a simple answer if there is one, i've now decided to go for 18x8 back and 17x7 front, i wont the rear's to stick out more than the stock 16 inch rims by 20mm and the fronts by 10mm so my question is wot ET do i need so i can get a rim to just fit without spacers and if the et number gets bigger does that throw the wheel into the arch or out. Its bloody hard picking an 18 and 17 inch rim because there's no point looking in a wheel shop or on line at the millions of rims avaliable because the ones you like might not be avalable in that size so i'm thinking i need to give the spec to a wheel company and then they can show me wots avaliable, also wot tyres do i need for those rim sizes.