I've got 18x7 wheels with 215/35/18 tires. The wheels have a +40 offset.

I was going to get 25mm spacers for the rear, but I've heard that the resulting +15 offset will rub and I don't want to roll my fenders.

Is anyone currently running this setup? What about 20mm spacers?

 

i was going to go with the 20mm to but with a 45mm ofset on the rims im now going with 10mm shim and 5mm spacer, but in your case i would go with the 20mm because you have 40mm offset on your rims, and like you said you dont want to roll your fenders