Tire Blowout Causes and Warning Signs to Watch

What causes a tire blowout?

A tire blowout is a sudden, explosive loss of air pressure caused by a structural failure in the tire. The most common underlying causes are underinflation, overloading, impact damage, and age-related deterioration. These conditions weaken the tire's internal structure, allowing heat to build up and causing the rubber and cords to separate.

Under Federal Motor Vehicle Safety Standard No. 139, which covers new radial tires for light vehicles, tread separation is defined as pulling away of the tread from the tire carcass, and sidewall separation is the parting of rubber from the cord material. These failures are often the final step before a blowout.

Understanding the basic anatomy of a tire helps you recognize risks. The tire consists of a tread that contacts the road, belts that provide strength, a carcass of cords that holds the shape, and an innerliner that contains the air. Each layer must stay bonded. When heat or damage breaks that bond, pressure can push the tread outward, causing a sudden failure. Check your tire construction types to know what is inside your tire.

Underinflation and overloading

Underinflation is one of the leading causes of blowouts. When tire pressure drops, the sidewall flexes more, generating heat that can break down the rubber and cause separation. Federal regulations require tire pressure monitoring systems on vehicles under 10,000 pounds to warn drivers when pressure falls 25 percent below the manufacturer's recommended cold inflation pressure. Pay attention to that warning light.

Overloading stresses the tire beyond its load rating, which also creates excessive heat. FMVSS No. 110 requires that the sum of the load ratings of the tires on an axle be at least equal to the axle's gross axle weight rating. Never exceed the maximum load rating printed on the sidewall, and consult the vehicle's placard for the correct pressure. Learn more about tire pressure basics and tire load index ratings.

Heat is the enemy of tires. Underinflation and overloading both increase flexing and friction, raising the internal temperature. Over time, this heat accelerates the breakdown of the rubber and the adhesion of the belts. Always check your tire pressure when the tires are cold, and never reduce pressure in an attempt to improve fuel economy. Keeping the recommended pressure also improves fuel efficiency; the U.S. Department of Energy reports that underinflated tires can lower gas mileage by about 0.2 percent for every 1 psi drop.

Mechanical damage: cuts, punctures, and impacts

Potholes, curbs, and road debris can damage the tire's internal structure even when the outside looks fine. A hard impact can break the belts or cause a bulge on the sidewall, which is a sign that the carcass has been weakened. Punctures in the tread can be repaired, but sidewall damage is not repairable and the tire must be replaced.

Inspect your tires after hitting a pothole or curb. A bulge or bubble in the sidewall is an immediate warning that the tire may blow out. Also check for cuts and scrapes that expose cord. See our guide on tire sidewall bulges.

Punctures from nails or screws can damage the belts, even if the tire holds air at first. If you notice a slow leak or find a foreign object embedded in the tread, have the tire inspected by a professional. Many punctures can be repaired in the tread area, but the tire must be removed from the wheel and inspected from the inside. Never plug a tire yourself if the puncture is near the sidewall or larger than a quarter inch.

Age and deterioration

Tires age even when they are not used. Heat, ozone, and UV light cause the rubber to dry out and crack. Dry rot, which appears as small cracks on the sidewall or in the tread grooves, can lead to tread separation. The DOT code on the sidewall tells you the week and year of manufacture; many manufacturers recommend replacing tires after six years, regardless of tread depth.

Retreaded passenger tires must meet the same structural requirements as new tires under FMVSS No. 117, but the casing must be free of exposed cords. Check retreads carefully for any sign of damage. For more on tire age, see tire age and dry rot and tire DOT date codes.

Environmental exposure accelerates aging. Parking in direct sunlight, extreme heat, or in areas with high ozone levels can shorten a tire's life. If your tires are more than six years old, have them inspected annually even if they look fine. The rubber compounds degrade over time, making the tire more susceptible to impact damage and separation.

Warning signs to watch for

Any of these signs suggests the tire structure is compromised. Do not drive on a tire with a visible bulge or deep cracks; have it inspected and replaced if necessary.

Vibration at highway speed often indicates a separated belt or an out-of-round tire. A squirming or pulling sensation can also signal a damaged sidewall. If the vibration persists after balancing and rotation, have the tire evaluated for internal damage.

• Vibration or wobbling at highway speeds, especially if it gets worse.
• A bulge or bubble on the sidewall.
• Cracks in the sidewall or between tread blocks.
• Tread wear indicators touching the road surface (1/16 inch remaining).
• TPMS warning light or frequent pressure loss.
• Uneven wear patterns, such as shoulder wear or cupping.
• Visible cord or fabric in cuts or abrasions.

How to prevent a blowout

Check tire pressure at least once a month and before long trips. Use the pressure listed on the vehicle's placard, not the maximum printed on the sidewall. Properly inflated tires also improve fuel economy; underinflated tires can reduce gas mileage by about 0.2% for every 1 psi drop.

Inspect tires for cuts, bulges, and foreign objects. Rotate tires according to the vehicle manufacturer's schedule, and replace them when tread depth is low or they show signs of age. See how to check tire pressure and tire treadwear indicators.

When buying new tires, choose ones that match your vehicle's load rating and speed rating. See our roundups for all-season tires, summer tires, winter tires, or all-terrain tires.

Also consider the age of the tire when you buy it. Look for a DOT code that is recent, and avoid tires that have been stored for years. Even new tires can be old if they have sat on a shelf. The date is your best indicator of freshness.

What to do during a blowout

Stay calm, keep a firm grip on the steering wheel, and do not slam on the brakes. Gradually ease off the accelerator and let the vehicle slow down. Once you are at a safe speed, steer to the shoulder and stop. Turn on your hazard lights and call for assistance.

Never suddenly brake or jerk the wheel, as that can cause a loss of control. Keep the wheel steady and maintain your lane until the speed drops below 25 mph. Then gently pull off the road.

After the vehicle is stopped, exit carefully and set up warning triangles. Do not attempt to change the tire on a live highway if you are not in a safe location. Call for roadside assistance and wait in a safe spot.

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Questions

What is the most common cause of tire blowouts?

Underinflation is a leading cause. Low pressure causes excessive flexing and heat, which can lead to tread separation over time. Overloading has a similar effect, so always keep the tires at the recommended pressure and avoid exceeding the load rating.

Can a tire blowout without warning?

Often there are early signs like vibration, bulges, or cracks. Regular inspection helps catch them before a blowout. A sudden impact from a large pothole can cause immediate failure, but audible or tactile cues are more common.

How often should I check my tire pressure?

At least once a month and before long trips. Use the pressure on the vehicle placard. Also check the spare tire, since it can lose pressure over time. And remember to check when the tires are cold for the most accurate reading.

Are sidewall bulges repairable?

No. A bulge indicates internal damage to the sidewall cords, and the tire should be replaced immediately. Driving on a bulging tire risks a blowout, so you should switch to a spare or call for assistance.

How long do tires last?

It varies by tread life and age. Many manufacturers recommend replacing tires after six years regardless of tread depth. Check the DOT code for the tire's age, and have them inspected annually if they are older.