Tires are expensive and buying used tires seem like a good bargain. However, this savings comes at the cost of assuming more risk. While most sensible people will choose tires with the best tread, this alone doesn’t insure against a possible tread separation or a tire blowout. The factors that affect this risk are the tire’s age as well as its history of use (or abuse) by the previous owner. Reasonably good-looking tread is not a solid indicator of the tire’s safety.
Poor Tire Care by the Previous Owner
Without a doubt, bad tread as well as uneven tread on a tire is dangerous because it compromises your car’s braking and handling. Furthermore, certain types of uneven tread wear indicate poor tire maintenance.
However, good tread by itself doesn’t mean that the used tire was not abused by the previous owner. Driving on severely under inflated tires for short periods before significant tread wear occurs will damage the tire’s rubber. For example, driving the length of a driveway on a flat will damage the tire sufficiently to make it unsafe. The astute person will recognize this by a ring of slightly discolored rubber on the sidewall.
When a tire ages, oxidation makes the rubber stiff and causes small cracks to form. Warm temperatures accelerate this process which is why aging tires are a greater problem in the southern states than farther north. Sun exposure as well as poor tire maintenance (especially tire under inflation) also contribute to tire aging. Manufacturers recommend tire replacement after six years, regardless of the mileage on them or the tread wear.
Therefore, a very old tire that has had little use can have perfect tread, look brand new, and yet pose a danger to the motorist that uses it. Cracks in the stiff and brittle rubber get larger and can eventually cause the tread to separate from the steel belts in the tire. Old tires are also vulnerable to blowouts.
How Good Looking Tires Get Old
How do tires get this old without tread wear? Spare tires left in a trunk for years, or left on a shelf in a garage are two possibilities. Some people do very little driving or have a second car that they only use on weekends. These old tires can make their way to a used tire bin at a gas station or tire store. Check the last four digits of the DOT number on the tire’s sidewall. These show the week and year that the tire was made. For example, if the last four digits are 3012, then the tire was manufactured on the 30th week of 2012.