Why Blowouts Happen—and How to Avoid Them

Underinflation

Underinflation is the easiest way to kill a tire. After all, air is what allows a tire to carry the weight of a vehicle and its cargo. Without proper air pressure, the internal components of the tire—fabric, steel, rubber, and composites—flex beyond their designed limits. What happens is much like bending a length of wire: Manipulate the metal long and far enough and it will overheat and snap. Try it with an old-style wire clothes hanger. (Warning: The failure point will be skin-burning hot.) Without proper air pressure, the tire’s internal pieces will overflex, weaken, and, eventually, fail.

Proper pressure for tires on recently produced cars can be found on the driver’s side door jamb. It’s true that the Tire Pressure Monitoring System (TPMS) has been mandatory on all cars, pickups, and sport-utility vehicles since 2007, but that system does not issue an alert until a tire is significantly underinflated. A responsible driver still has to check tire pressure by hand or have someone such as a tire dealer do it for him.

If you drive any distance with a radically underinflated tire, have a professional demount the tire from the wheel and inspect its inside for any damage the low pressure might have caused. The definition of “radically underinflated” for your tire and vehicle combination can be found on your tiremaker’s website: If the pressure drops much below 20 psi, the extra-cautious will want to have their tire inspected by a pro.

Overloading

Overloading a vehicle can also fatally damage a tire. Just because your pickup’s bed will accept a full load of free mulch from the recycling center doesn’t mean your tires can carry the weight, especially if they’re underinflated. When pulling a heavy-laden trailer with your SUV, your 350-pound brother-in-law might have to find another ride.

To be sure about all this, you’ll have to find your vehicle’s Gross Vehicular Weight Rating (it’s on the same placard as the recommended tire pressure) and do the math. Those who haul extra-heavy loads can increase a tire’s weight-carrying capacity by raising pressure to the “maximum load,” indicated by the”maximum pressure” number found on a tire sidewall. The number molded into the tire tells the maximum weight the tire can carry if the tire is inflated to that maximum pressure.

Potholes

Another way to fatally injure a tire, especially with today’s ultralow-profile rubber, is to slam into pothole, driveway lip, or other road hazard. The impact pinches the tire’s internals between wheel and obstacle. If the hit is hard enough, it can cut or fray the internals. Sometimes the pothole will cut all the way through fabric and rubber, and the tire will die right there. Other times the damage won’t show up for months. Which brings us to:

The Slow Death

Commonly a tire suffers the damage that will cause its death long before it fails. Sometime people forget to check their tire pressure—maybe the minivan was hovering just above the TPMS warning threshold when the high school football team’s offensive linemen hopped in. Perhaps a driver doesn’t realize he or she has a slow leak (or procrastinates about it) and motors 20 miles before getting a repair. Every now and then, a teen driver forgets to mention that encounter with the pothole.

Any of these can accelerate a tire’s death. Perhaps months later, when the vehicle is loaded with the entire family and rolling toward a vacation destination, the combination of the heavy load, ambient temperatures in the 90s F, and highway speed limits stresses the tire beyond its limits. The previously damaged tire can take no more and fails.