I'm planning on running 225's for autocross, since the 205's stock on the Volvo are just plain too skinny. For that I need a 7" wheel, instead of the stock 6.5". So I have these picked out: 4 New 15x7 5x108 Voxx MG3 Silver Wheels Rims | eBay

Now my question is, would it be better to run the +20 offset or the +38 offset type of these wheels, since anything larger than a 205 rubs, but since they're for autocross only, I don't mind. The stock Volvo 850 offset is +43. I was thinking I should go with the +25 because it will push the wheel and tire out further, and hopefully eliminate some rubbing.

 

You should roll the fender lips both front and back to keep them from cutting into your sidewalls. It's likely the speed and sharp directional changes will put your sidewalls in danger

You might want to try that question on wheel offset on Volvospeed too.