Tire Sidewall Cracks: How to Tell If They Are Serious

What are sidewall cracks?

The sidewall is the portion of a tire between the tread and the bead, as defined in federal safety standards. Cracking in this area is any parting within the sidewall rubber that extends to the cord material. The federal standard for new pneumatic radial tires for light vehicles (49 CFR 571.139) explicitly states that a tire must show no visual evidence of cracking before it can be certified for use. This definition is important: a crack that reaches the cords means the structural integrity of the tire is compromised.

Not all cracks are equal. Surface crazing, a network of tiny shallow cracks, can appear as the rubber ages. These may not reach the cords and might be considered cosmetic. However, determining whether a crack is superficial or structural requires careful inspection. The key question is whether you can see fabric or steel cords in the crack. If yes, the tire is unsafe and must be replaced.

• Cracks that expose cords are always serious.
• Deep cracks that look like cuts may also be serious even if cords are not yet visible.
• Sidewall bulges often accompany internal damage and indicate a separate problem.

What causes sidewall cracks?

Sidewall rubber is a blend of compounds that must flex constantly while the tire rolls. Over time, this rubber degrades due to oxidation, ozone exposure, UV radiation, and temperature cycles. The U.S. Tire Manufacturers Association (USTMA) notes that tire manufacturers continuously work to improve durability, but no tire lasts forever. Age is a primary factor: even if the tread looks fine, the sidewall rubber can harden and lose its flexibility, leading to cracks.

Underinflation is another cause. When a tire is run at low pressure, the sidewall flexes more than intended, generating heat and mechanical stress. Over time, this can lead to cracking and even separation. Federal standards for tire pressure monitoring systems (49 CFR 571.138) require a warning when pressure falls 25% below the recommended level, but many drivers ignore the warning. Keeping tires at the vehicle manufacturer's recommended pressure, as indicated on the door placard, reduces sidewall stress.

Other contributors include chemical exposure (such as from tire dressings containing petroleum distillers), prolonged storage without weight on the tire, and simply years of service. The Tire Industry Association (TIA) emphasizes that tire inspection is the first step in safety, and trained technicians look for cracking during routine checks.

How to inspect sidewall cracks

You can perform a basic sidewall inspection with a good light and a little time. Start by cleaning the sidewall with soap and water to remove dirt and dressings, which can hide cracks. Then run your fingers along the sidewall to feel for rough spots or bulges. Use a flashlight to look closely at the area between the tread shoulder and the bead.

Pay special attention to the area where the sidewall meets the tread and near the bead, as these are common locations for cracks. Also check the inner sidewall, though it may require turning the front wheels to see. If you find any crack, probe it gently with a plastic pick or a screwdriver. Do not use a sharp metal object that could damage the tire further. The goal is to see whether the crack has depth that reaches the cord layer.

A more thorough inspection should be done by a professional, especially if you see any cracking at all. The TIA offers technician training and recommends that drivers have tires inspected at least once a month, or before long trips. For detailed guidance on reading sidewall markings and DOT codes, see our learn article on sidewall markings.

When to replace: the serious signs

The clearest sign that a sidewall crack is serious is the appearance of cords. If you see fabric or steel wires in the crack, the tire is structurally unsound and must be replaced before driving. Even if you cannot see cords but the crack is deep enough to insert a tool more than a fraction of an inch, treat it as serious. Federal standards for retreaded tires (49 CFR 571.117) require that a casing show no exposed cords before being retreaded, which underscores how a single crack reaching the cord makes the tire unusable.

Other signs that point to replacement include cracks combined with a bulging sidewall, which may indicate internal belt separation. Cracks that run along the sidewall for several inches, or that appear to be cuts rather than weather cracks, are also ground for replacing the tire. When in doubt, have a professional inspect the tire. If you are replacing one tire, the others may be at similar risk due to age; consider replacing a set. For advice on when to replace tires based on age and wear, see our replacement guidelines.

• Visible cords: replace immediately.
• Crack depth greater than a hairline: professional inspection.
• Bulge or separation near the crack: replace.
• Crack on more than one tire: consider full set replacement.

How to prevent sidewall cracks

The best prevention is proper tire care. Keep tires inflated to the vehicle manufacturer's recommended pressure, not the maximum printed on the sidewall. Underinflation increases sidewall flex and heat buildup, accelerating cracking. Check pressure monthly, and before long trips, using a reliable gauge. Our [tire pressure basics](/learn/tire-pressure-basics/ page has more details.

Avoid harsh cleaning products and petroleum-based tire dressings. Some dressings can accelerate rubber degradation. Also, store tires away from direct sunlight and ozone sources like electric motors. If you have seasonal tires, store them in a cool, dry place out of the sun. Regularly inspect your tires for any signs of aging, and note the manufacture date from the DOT code. Tires older than six years, even with good tread, should be inspected by a professional; many manufacturers recommend replacement after ten years regardless of use. See our tire age and dry rot guide for more on aging.

What to pick for your use

Questions

Can I drive on a tire with small sidewall cracks?

Small, hairline surface cracks may be cosmetic and not an immediate hazard, but they indicate aging. If you are not sure whether the crack reaches the cords, have a professional inspect the tire. Even if shallow, cracks are a sign that the tire is nearing the end of its service life.

How deep does a sidewall crack have to be before it is dangerous?

Any crack that exposes or extends to the cord material is dangerous. A crack that is deep enough to catch a fingernail or a tool should be taken seriously. Federal standards require that a new tire show no cracking, so any crack in a used tire should be evaluated carefully.

What causes sidewall cracks besides aging?

Underinflation is a major cause because it increases sidewall flex and heat. Ozone, UV radiation, and certain chemical tire dressings can also degrade the rubber. Proper tire pressure and avoiding harsh chemicals can reduce the risk.

Are sidewall cracks covered by warranty?

Warranty coverage varies by manufacturer and depends on the cause. Cracks due to aging or environmental exposure are often not covered, while cracks due to a manufacturing defect might be. Check the tire's warranty documentation and contact the manufacturer. The DOT code on the sidewall can help identify the age.

Can sidewall cracks be repaired?

Repairing sidewall cracks is not recommended. Patching or plugging a sidewall is not a recognized repair procedure due to the high flex and stress in that area. If the crack is serious, the tire must be replaced. See our tire repair vs replace article for more details.