I had 17 inch wheels, 7 inch width and 45mm offset covered in 215/40 rubber on the front with standard Bilsteins and it was very close to the strut but it did NOT touch.
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Rears had pleanty of clearance with 235/40 rubber over 8x17inch rims on 45mm offset.
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If you are putting rims on that are 1/2 inch wider then you would have to move the offset 7mm
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(half of half an inch) to be on the safe side and retain the gap between wheel and strut, therefore a 38mm offset would be correct but I would be cautious of the tyre rubber overhanging the rims.
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