I've ran 12mm and 15mm I my M6 for the past two years with zero issues. I've recently changed wheels and tyres and now run smaller spacers. Ever since I changed I've had a wheel wobble between 62 and 74 mph. I took the car back to National Tyres who immediately blamed the spacers but when I pointed out I'd ran them in the past without issue and asked about how a wider wheel with a bigger offset would effect balancing they didn't have an answer. I'm not convinced the bloke even knew what offset was. They said the wheel and tyre were perfectly balanced according to "the machine" but the issue is still there. Is the tyre fitter just a bit ****, or will the spacer be having an effect?