How's the tread on your tires? A better question for the sake of saving your life is this: how old are your tires? When tread gets thin, we know to replace our tires, but most people don't know that the age of the tires, even a spare that is in the trunk of the car, is of extreme importance. If you expect when you buy a tire that it should be safe until the tread wears thin, you believe what most consumers are led to believe. But regardless of their tread depth, tires that are more than 6 years old are unsafe.
When I hear about single car wrecks, I usually wonder about the age of the tires. Tires degrade with age. It's easier for tread separation to occur because of reduced adhesion between the belts. Age degradation is invisible, so it sneaks up on people, and it occurs regardless of tread use and wear.
Natural rubber is particularly susceptible to oxidation, one of the factors that causes older tires to weaken. Degradation of a spare in the trunk occurs just as fast as the breakdown occurring in tires touching the road. You can't put that old but fully treaded tire on and drive safely. Tires that you buy have usually been stored for some time in a tire wholesaler's or retailer's warehouse. They might be brand new to you but already mid-age or older in reality.
Remember the danger point. It is 6 years of age on a tire. How can you tell the age of your tires? It's very simple. A 10 to 12 digit code of letters and numbers preceded by DOT is molded onto every tire. It's called the Tire Identification Number. The last four digits tell the age. Forget about all the other letters and numbers that identify the manufacturer, tire size, and manufacturing location. Concentrate on the last 4, because they identify which week and year the tire was built. For example, if those numbers are 5106, the tire was made in week 51 of 2006. It's nearly time to get rid of it for your safety.