I will strongly second that opinion - if you get the 18" wheels you should also get dedicated winter tires. Actually, I feel that all car owners should have dedicated winter tires. Modern vehicles use many technological advances for handling, traction, and safety (and the XC90 is tops in this respect!) but all of these abilities are limited by the stickiness of your four contact patches. Always use the best tires available for your conditions. Approximately $1,500 for winter tires and nice wheels is a drop in the bucket in relation to the $45,000 cost of the car.