Take this for just my out look...I know that tires are to be replaced when they are 6 to 7 years old...but if my tires don't show any sign of wear or cracking I will only replaced the front tires at that time...the rear tires are dual's & if one of them blows out I still have the other one to get to a safe stop...but if a front tire blows out you maybe headed for the ditch...reason for my way of thinking is 48 years of being a truck driver with no wrecks...and I am not selling tires for a living...