Ciao Matteo
I have 17x8 with 225 45's et35 and have no rubbing issues at all.
This size is almost identical to your 18x8 225 40 et35.
Many people on the FRS project tire calculator site claim that it will fit fine too. You can look for yourself here
http://www.frsproject.com/tire_size.php
Also, on the wheel fitment thread
http://www.ft86club.com/forums/showthread.php?t=11393
There is a chart with all of the fitments. 18x8 ET35 is listed as "perfect fitment"
Here is a thread with the exact same size wheels + tires
http://www.ft86club.com/forums/showthread.php?t=11393