Tire Underinflation Damage: Heat, Wear, and Possible Failure

What underinflation does to a tire

An underinflated tire does not hold its designed shape. When pressure is too low, the tire's sidewalls flex more as it rolls, and the contact patch changes shape. Instead of the tread sitting flat, the center of the tread lifts slightly, and the shoulders take more of the load. This increased flex generates heat inside the tire, and that heat is the root cause of most underinflation damage.

Heat is the enemy of tire rubber and the internal structure. Federal safety standards define separations and cracking as failures, and they are typically the result of running a tire under conditions it was not designed for. Running a tire at low pressure is one of those conditions. Learn more about tire pressure basics and how heat damages tires.

Heat build-up and its consequences

Every tire flexes as it rolls, and that flexing produces heat. The lower the pressure, the more the tire deflects, and the more heat it generates. Heat weakens the bond between the rubber and the internal cords. Over time, this can lead to ply separation, cord separation, and tread separation. The definitions in Federal Motor Vehicle Safety Standard No. 139 list these separations as failures, which means a tire displaying them is not safe to continue using.

We also know from the U.S. Department of Energy that underinflated tires reduce gas mileage by about 0.2% for every 1 psi drop. That is not directly damage, but it is a sign that the tire is not running efficiently. Proper tire pressure is important for both safety and efficiency.

• Ply separation: rubber compound parting between plies
• Cord separation: cords parting from rubber
• Tread separation: tread pulling away from carcass
• Sidewall separation: sidewall rubber parting from cords
• Innerliner separation: inner layer parting from carcass
• Bead separation: bond break in the bead area
• Cracking: any parting reaching cord material
• Chunking: pieces breaking away

Shoulder wear pattern

When a tire is underinflated, the tread does not make full contact with the road. The center of the tread bows upward, so the outer edges, the shoulders, carry more of the vehicle's weight. This causes the shoulders to wear faster than the center. If you see a tire with the outer edges down to the wear indicators while the center still has tread, underinflation is a likely cause.

Treadwear indicators are required by federal law to show when a tire is worn to 1/16 inch. They are molded into the main grooves. When the tread is flush with those indicators, the tire is legally worn out. But shoulder wear may expose the indicators on the edges first. Learn about shoulder wear causes and how treadwear indicators work.

Structural damage and failure modes

The most serious result of underinflation is structural damage. Heat and flexing can break the bond between rubber and cords, leading to separations. The federal standards define bead separation, tread separation, sidewall separation, ply separation, and innerliner separation as failures. These conditions are not repairable; once a tire separates, it must be replaced.

Other damage includes cracking in the sidewall or tread, chunking (pieces breaking off), and open splices. All of these are listed in the FMVSS definitions as things that disqualify a tire from use. If you notice any of these signs, the tire is unsafe and should be taken out of service.

Detecting underinflation damage

Check your tire pressure monthly with a reliable gauge, and always check when the tires are cold. The correct pressure is on a sticker in the driver's side door jamb, not on the tire sidewall. If your vehicle has a tire pressure monitoring system, it will warn you when pressure is 25% below the recommended level, but that is not a reason to wait. By the time the light comes on, the tire may have already been driven at low pressure for a while.

Look for signs of damage: unusual wear on the shoulders, bulges or blisters on the sidewall, cracks in the rubber, or pieces missing from the tread. These are all visual clues that the tire has suffered from underinflation. Learn how to check tire pressure and what a sidewall bulge means.

When replacement is required

Separations, cracks that reach the cords, bulges, or any sign of structural failure means the tire cannot be repaired and must be replaced. Running a tire that is underinflated may also cause damage that is not visible externally. If you have been driving on a seriously underinflated tire for a long distance, it is wise to have it inspected by a professional before continuing to use it.

Replacing a damaged tire is not optional. The structural integrity of the tire is compromised, and a blowout can occur at any speed. If you need to buy a new tire, use our buying guides to compare options for your vehicle and driving needs. Understand when to replace tires and then look at the best all-season tires for a reliable replacement.

Preventing underinflation damage

The best way to avoid underinflation damage is to maintain the correct pressure. Check pressure at least once a month and before long trips. Use the pressure recommended on the vehicle placard, not the maximum printed on the sidewall. A TPMS can alert you to a drop, but it does not prevent the damage from occurring if you ignore the warning.

If you need new tires, choose them based on your vehicle and driving conditions. Properly inflated tires will last longer and perform better, and they will not suffer the heat and wear that comes from underinflation. Review tire pressure monitoring basics and then browse our car and SUV tire guide for suitable replacement options.

What to pick for your use

Questions

How low is too low for tire pressure?

The tire pressure monitoring system on vehicles must warn you when pressure is 25% below the recommended cold inflation pressure. However, even a few psi below the placard value can increase heat and wear, so it is best to keep tires at the exact recommended pressure.

Can underinflated tires cause a blowout?

Yes. Underinflation generates heat that can lead to ply separation, tread separation, or other structural failures. A tire that has suffered these failures is at high risk of a blowout, especially at highway speeds.

Should I repair or replace a tire with underinflation damage?

Replace it if there is any separation, cracking that reaches cords, bulging, or chunking. These conditions cannot be repaired. If the tire only shows shoulder wear without structural damage, it may be worn out but not necessarily unsafe; however, a professional inspection is recommended.

How often should I check tire pressure?

Check at least once a month and before long trips, when the tires are cold. Also check after any significant temperature change, as pressure drops in cold weather.

Does underinflation affect fuel economy?

Yes. The U.S. Department of Energy reports that gas mileage drops about 0.2% for every 1 psi drop in the average pressure of all tires. Keeping tires properly inflated improves efficiency and helps prevent the damage described in this article.