I am going with a set of 225/40/18 tires..
if i buy 18 x 7.5 rims, what is the minimum offset i need without any rubbing?..
if i buy 18 x 8 rims, what is the minimum offset i need?

my car currently has H&R sport spring drop.....

thank you

 

The closer to +55 the better. Absolute minumum would be +45. The lower the offset will yield a higher probability of rubbing.