Your "new" tires could be six years old and ready to disintegrate on the highway. Tire rubber dries out after six years, but American companies are allowed to sell expired tires long after they wear out. This 20/20 investigation found that the "new" tires on sale at Sears and Walmart can be up to 12 years old!
If you want to know the age of your tires, all tires bear a Department of Transportation number hidden on the inner wheel wall. At the end of the number is a four-digit sequence that shows the week and year the tire was made. Tires with the notation 3502 were made in the 35th week of 2002. If you only see three digits, get new tires immediately; your tires are from the 90's and are way past their effective lifespan.