Originally Posted by 28HopUp
I guess I should chime in!
I have had zero problems with the Volvo XC90 wheels 16x7". Here is the thread I made about them:
New Volvo wheels for my 2012 SE Hatch
The Volvo hub bore IS slightly larger, but the 5x108 lug pattern allows the wheels to be centered once the lug nuts are properly secured. I have had no issues with vibration. But here's the caveot - this car is a commuter vehicle only and isn't driven agressively at all. So I am not putting undo strain on the wheel lugs (IMO) through normal driving. If I was autocrossing the car, then I would use wheels with the correct bore size so the wheel hub bares the corrnering load force.
In terms of determining wheel options, offset is very important, along with bore size (you cannot use a non-factory wheel with a bore size smaller than that on a Focus). But another consideration is maintaining sufficient clearance around your brake calipers. Stock OEM brakes are not massive, but you need to ensure that the spokes of the new wheel will clear the calipers (in most cases you'll be fine I think, but it's still something to consider).
In talking with a professional wheel / tire shop -- and the principal who I consider to be a pretty decent source of accurate info -- he said go out of your way to stay with the stock ET value. He had had direct experience, decreasing the ET value (i.e. decreasing the back-set) on his shop vehicle. It went from tracking really well, to a circumstance of very poor steering.