Our reader was washing their car and noticed what looked like cracks in the sidewall of their tyre. They want to know whether this is something they should worry about.

It depends how big the cracks are

Tiny cracks that appear in the tread blocks aren’t anything to worry about. Our reader’s cracks were deeper and longer and featured in the tyre’s side. In this case, it’s a sign that the tyres are coming to the end of their life.

What cracks mean

As tyres age, the chemicals in them start to age too. It’s a bit like they dry out. Deep cracks are a sign that the sidewall and/or tread are starting to separate from the body of the tyre.

It’s worth saying that cracks in tyres can be a particular problem in caravans and motorhomes, for reasons we’ll explain below.

Why are cracks a safety problem?

Cracks in the sidewall can mean that moisture is getting into the tyre’s structure. Beneath the rubber of tyres is a mesh of steel wires. These cords give the tyres their strength and stiffness. Obviously if water gets into these it can cause corrosion which eventually causes the cords to fail. The result? The tyre will suddenly fail or blow out.

What leads to cracks?

Tyres have anti-ageing chemicals in them. These are distributed around the tyre when they’re driven on. The older a tyre gets, the less effective these chemicals become. This results in the outside of the tyre becoming more brittle, which ends up with cracks appearing.

Being stationary can also cause tyres to crack because tyres that aren’t moving aren’t having their anti-ageing chemicals distributed around them. Having the sun shining on them causes problems too.

The tyre absorbs the UV rays in sunlight. This does two things: it causes the tyres to heat up meaning they expand and contract. And the UV rays cause the tyre’s compound to degrade. The result of both these things is cracks in the tyres.

What can you do about it?

Unfortunately, once cracks appear in tyres, it’s too late to do anything about them. You should replace the tyres with cracks in and then try to prevent them forming in the first place. If you have a caravan or motorhome, when it’s laid up over winter, try to protect the tyres from sunlight by covering them. And if you can, rotate the wheels on a monthly basis.

Also, check the age of your tyres. The older they are the more likely they are to have cracks in them. You will find the age on the sidewall. It’s in an embossed box and features four digits which signify the week and the year tyres were built.

Will cracked tyres fail the MOT?

Cracked tyres are one of those weird ones where it’s not actually illegal to have cracked tyres on your car. But if you take your motor for its MOT, it will fail the test if it does have cracks in the tyres.

This is because the MOT is a safety test above everything. Cracks mean the structure of the tyre has been compromised and it could fail at any moment, putting you, your passengers and other road users at risk.

James Foxall

I’ve been writing about cars and motoring for more than 25 years. My career started on a long-departed classic car weekly magazine called AutoClassic. I’ve since pitched up at Autosport, Auto Express, the News of the World, Sunday Times and most recently the Daily Telegraph. When I’m not writing about cars and motoring, I’m probably doing some kind of sport or working in my garden.