I need to know if 18x8.5 with 42mm offset and 225x40x18 tires would ride good or if I would run into issues.

 

Might be a little tight on the inside ... a 225 tire is setup for a 7.5 wheel...are you trying to have a wheel wider then the tire?. The 8,5 will set inboard a half inch further then stock, SS anyways. Are you lowered?'' If so then you will have rubbing issues when turned. I rub occasionally with the stockers.