It is recommended that you replace all four tires. New tires grip the road better than those that have been worn down, so it*s best to keep all the tires on your vehicle at the same tread level. However, if for financial or other reasons you can only replace two, put the two new tires on the rear axle of your car. Never replace only one tire - you should get at least two.
〉 Answered on Apr 6th, 2010 by Denise Koeth, Managing Editor at Tire Review Magazine
Not necessarily. First you should start by having all of your tires inspected. If your tires are at 4/32nds or below I would suggest replacing all 4. If any of your tires are above 4/32nds and not showing signs of irregular wear at inspection and the dealer recommends that you replace less than 4, then it is recommended that you replace them in pairs on the same axle, because your Grand Marquis is 2 wheel drive. If you replace only 2, the newer tires should be installed on the rear axle. This will provide you with better wet grip, less chance of hydroplaning and provide greater vehicle stability. If you have any other questions please let me know.
〉 Answered on Apr 6th, 2010 by Julie Scroggins, Vice President, CFO at Waukegan Tire and Supply Company Inc.