I bought the 18" premium wheels with the car to upgrade the appearance.
Yesterday while traveling from Chicago to Bloomington, Ind I had a blowout that could not be repaired due to hitting some metal debris on the road.
Try finding an 18" tire!Not one tire dealer including Volvo dealers had one in stock! I had to have Tirerack. com ship one Fed Ex to me in Bloomington to get one at significant expense. Now I'm getting a full size spare since I travel a lot on the roads. Just an FYI for anyone with the 18"wheels you will be SOL on the road gimping around on the mini-spare.
Move to Europe - we have the tires ;-) )