Tyre sidewall cracks: ageing, damage, and when it is unsafe

Small, shallow cracks on a tyre sidewall are usually a sign of age. Rubber hardens and splits on the surface after years of sun, heat and ozone, much as an old rubber band does. Michelin treats such cracks as a warning that the tyre is nearing the end of its life and that it is time to plan a replacement, not as an emergency. Exposed cords, cuts that reach the casing and any bulge are different: those tyres should come off the car now, and deep cracks need a professional’s eye. Indian rules say a tyre with any of its casing fabric exposed is not in a sound condition, and a tyre in that state should not be on a public road.

What causes tyre sidewall cracking

Age and weather. Rubber degrades over time through heat cycles, ultraviolet light and ozone, and Michelin notes that much of this happens in ways that are not visible on the surface. Cracks are the visible part, and Michelin links them to both age and exposure to sun and ozone.

Sun while parked. MRF’s warranty specifically excludes damage to tyres exposed to direct sunlight for long periods while fitted to a stationary vehicle, a sign that tyre makers treat a car left standing in the sun as a real cause of damage.

Tyre shine and harsh cleaners. Michelin says that chemicals used to make tyres shine can strip out the protective agents in the rubber and expose the sidewall to cracking sooner. It specifically advises against cleaning sidewalls with products containing silicone.

Low use. A spare tyre or a second car that is rarely driven still ages. Michelin’s age guidance applies to spares as much as to tyres on the road.

Cracks, cuts and bulges: telling them apart

Michelin groups sidewall damage into three kinds, and they call for different responses.

Cracks from ageing are many, fine and spread around the tyre. They are a sign of age rather than a single event.

Cuts come from sharp stones, kerbs or debris and are usually a single gash. A shallow cut may not be an immediate danger, but if it is deep it may have damaged the carcass ply, the layer of cords under the rubber that contains the air. Then the tyre can lose pressure suddenly and cannot be repaired. Michelin’s point is that a non-expert cannot judge the depth reliably, so any cut deserves a professional look.

Bulges look like a bubble on the sidewall. They mean the carcass behind the rubber has already been broken, usually by a pothole or kerb. A bulged tyre is unsafe at any speed; our guide to tyre bulges explains why.

One thing that is not damage: Michelin notes that slight ripples or dips in the sidewall of a radial tyre are normal where the internal plies overlap. A shallow, even indentation is not a bulge.

When is a cracked tyre unsafe to drive?

Replace the tyre if any of these apply:

• You can see fabric or cords. Rule 94 of the Central Motor Vehicles Rules says a tyre is not in good and sound condition if any of the fabric of its casing is exposed through wear or an unvulcanised cut.
• There is swelling. The same rule treats signs of failure such as local deformation or swelling as unsound.
• The tyre is ten years old. Michelin recommends replacing any tyre, spare included, ten years after its date of manufacture, whatever it looks like.

Have it inspected by a professional soon if any of these apply:

• The cracks look deep, or are spreading. Michelin’s point about cuts applies here too: only someone trained can judge how deep damage goes.
• The tyre is more than five years old. Michelin recommends a professional inspection at least once a year from that point.
• The car has started to vibrate or pull, especially after hitting something. Michelin notes damage can be on the inner sidewall, out of sight.

If the cracks are fine and limited to the surface, the tyre may have life left, but it is ageing. Look up its manufacture date with our tyre age checker, and read our guide to tyre age and expiry dates.

Can sidewall cracks be repaired?

No. Michelin is clear that a punctured or cut sidewall cannot be repaired, because a repair cannot give back the flexing that the sidewall must do on every turn of the wheel. Tread punctures can be mended; sidewall damage cannot. And since Michelin warns that shine chemicals strip the rubber’s protective agents, products sold to make a sidewall look new are best avoided.

Does the warranty cover sidewall cracking?

Generally not, unless the inspection finds a manufacturing defect. Warranties cover faults in materials and workmanship. Cracking from age, sun exposure or chemicals is treated as wear or misuse; MRF’s policy names prolonged sun exposure on a parked vehicle as an exclusion. If cracks appear on a tyre that is only a year or two old and has been looked after, it is reasonable to ask the dealer to have it inspected. Our tyre warranty guide explains the process.

How to slow sidewall cracking

• Keep the tyres at the pressure on your car’s placard. Michelin lists correct pressure first in its advice on sidewall care.
• Park in shade or under cover where you can, especially if the car stands for days at a time.
• Clean tyres with water rather than chemical or silicone shine products.
• Look at all four sidewalls, and the spare, every few weeks. Turn the steering to full lock to see the inner face of the front tyres.
• Note the manufacture date when you buy, so you know when the five-year inspections and the ten-year limit fall.