You should always get four new tires, especially if the tires you are replacing are worn. The difference in tread depth could cause uneven wear and other ride problems. Especially with 4-wheel drive vehicles, all tires should be the same size, tread depth, tread pattern and brand.
〉 Answered on Feb 17th, 2010 by Denise Koeth, Managing Editor at Tire Review Magazine
Yes being 4 Wheel Drive does make a difference. We recommend replacing all 4 tires and here is why. The overall diameters of the tires must be the same. If they are not the vehicle interprets it as two tires spinning at a different rate and thinks two tires are slipping. It can also damage the transmission/transfer case/4 wheel drive unit. Replacing all 4, although costly up front, is a solid investment. I encourage you to make sure the new tires meet or exceed the load/performance rating of the tires that originally came on the vehicle.
〉 Answered on Feb 11th, 2010 by Julie Scroggins, Vice President, CFO at Waukegan Tire and Supply Company Inc.