Ive had my rims for a good 3yrs now, weren't cheap... sold the stocks a long time ago (rims were a bday present)

They told me the law is you can only go one inch lower or higher than what the tyre placard says. As youve probably figured out, it says 16inches

I told him I thought it was legal to go up by 2 inches and he told me only if its its cleared by an engineer

As jono said, the newer models of the cl9 came out with 17 inch rims so therefore 18 inch rims would be no problem

I know its easily cleared... I just want to have a letter (or whatever) saying that its fine for the future (just in case)

Ok fine if I had 20inch Dolce's on my car I'd wear it because youre asking for trouble....but my car is far from anything like that