40mm offset will be 12.5mm closer to the fender. Going wider on the wheels (is stock 18x7?) will also push it closer to both the fender and the shock.
I'm pretty sure stock MS3 wheels are 18x7, so going to an 18x8 +40 will put your tire about an inch closer to the fender. Stick your hand in between your tire and fender. Do you have an inch to spare?