Why it’s dangerous to drive with a bulging tyre

Replace any tyre that has a bulging sidewall like this. It is potentially dangerous

Having a bulging tyre - a lump in the side of the tyre - should prompt drivers to take immediate action.

Tyres lead a tough life. They’re subjected to a variety punishments from Britain’s ravaged roads, with potholes, crumbling verges, speed bumps and aggressive kerbs all taking their toll.

The result can see a bulge, typically about the size of the top of an egg, appear. It means the materials within the tough sidewall have been weakened. The next thing that could happen is the bulging tyre suffers a blow out - effectively explodes - and that could possibly lead to a loss of control of the car.

That’s why it’s important to check your car’s tyres on a regular basis. Green Flag technical expert, Nick Reid, has written a helpful guide to inspecting tyres, which covers setting the correct air pressure, checking the tread depth and carrying out a visual inspection.

A bulge can appear on either side of a tyre. Therefore it’s important to look at both the outer and inner sidewalls. Checking the inner sidewall is best done on a level surface, with the engine off, handbrake applied and car left in gear. A torch will help you get a clearer view, but if you have trouble, any local garage or tyre fitter will be happy to help.

What is a tyre sidewall?

The sidewall is made from extra-thick rubber and plies – strong materials that give structure, strength and shape to a tyre - and runs from the bead that seals the tyre against the wheel rim down to the tread. It gives a tyre its lateral stability, so it’s an important element of driving safely.

Potholes damage tyre sidewalls, leading to a bulge

However, with potholes lurking around every corner, tyres face all manner of punishment in the line of service. If a tyre hits a pothole or obstacle, such as a kerb, with sufficient force, then the sidewall’s structural integrity can be damaged and the rubber can separate from the plies. This allows air to escape, causing the egg-shaped bulge in the sidewall.

A bulging tyre will fail the MOT test

Just as a bald tyre would fail an MOT test, so would a bulging tyre sidewall, as it’s considered a serious safety risk. If the tyre were to burst at speed, it could cause the driver to lose control of their vehicle, potentially resulting in an accident.

And bear in mind that a bulging tyre can’t be repaired. So anyone that finds a bulge in one of their car’s tyres should either replace it with a spare wheel, especially if you have a long journey to complete, or have a tyre fitter replace the tyre. Most tyre makers and tyre fitters have a handy online branch finder that lets drivers type in their postcode and locate their nearest fitter.

Very occasionally, a bulging tyre may be a sign of a manufacturing defect, in which case the tyre fitter can return it to the maker and customers may be entitled to a refund or free replacement tyre.

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(For vehicles 10 years & under on our closest equivalent UK cover)