I need to buy winter wheels and tyres as my s3 and me are in Oslo this winter. My current rim size is the factory supplied 18"x7.5j ET54. Can someone tell me what range of offset I can get away with? e.g. would a ET35 fit or can I go no lower than ET45 for example?. I'm planning on buying secondhand (as there are loads for sale here) and clearly this is important. Also can I go smaller than 18" rim i.e. 17" or even 16"?