AudiForums.com - Wheel Spacers and tire size

I have a set of 18x8.5 wheels that have a 245/45 tire, when I test fitted them to my 00 A6 Avant they tire very slightly rubed on the inside suspension due to the large tire (previsouly on an A8). So in order to correct the problem I got a set of 20mm spacers, then after ordering I thought well 20mm might be too much and put the wheel out too far and would hit the fender during suspension compression after hitting a bump. So my question is if I were to take it to one of my local european tuning shops could they somehow test if it will fit (by measuring pehaps) without me having to open my package so I could exchane them for 10 or 15 mm. Or if anyone could give me their opinion about whether you think 20mm would cause a problem, that would be greatly appreciated, thanks!