Hi, Welcome to the forum...
I'm guessing that your wheels are BBS "RA's" I run 10mm spacers all round with no problems, I did try doubling up on the rears to 20mm but found that outer tire walls scrubbed lightly when 4 up, and getting over speed bumps etc, so reverted to the 10mm set up, which gives a nice subtle look...
I run 185 60 14 Dunlops on standard 16v springs, and have no clearance problems with the 10mm spacers.
Thom