A tyre is built from layers of rubber, fabric and steel cords. The cords carry the load and hold air pressure in. If a cord layer breaks, air pushes into the sidewall rubber and forms a visible lump. It can look like a golf ball under the surface, or a slightly raised oval, and sometimes only shows when the tyre is under load.
What causes a sidewall bulge
- Pothole or kerb impact. A hard hit can pinch the tyre between the road and the wheel rim and snap internal cords. Our blog covers pothole tyre damage.
- Driving on low pressure. A soft tyre flexes more, which stresses the sidewall.
- Impact with debris. Hitting an object at speed can damage the casing without puncturing the tread.
- Age and wear. Old tyres with cracking rubber are less able to resist damage.
- Overloading. Carrying more than the tyre load rating allows adds heat and strain.
Damage does not always show immediately. A bulge can appear days after an impact, which is why it is worth inspecting your tyres after any hard knock.
Why it is unsafe to drive on
The weakened section can burst without warning, particularly at higher speeds or when the tyre heats up. That is the kind of sudden failure described in our motorway blowout guide. A tyre with a bulge fails the legal safety standard, and there is no repair for it. Driving on a tyre with a visible sidewall bulge risks both your safety and a penalty if it is spotted.
Do not try to deflate it, pierce it or push it back in. The only fix is replacement.
Checking your tyres for bulges
- Park on level ground and inspect each tyre all the way around, including the inner sidewall facing the engine bay or the car underside.
- Run a gloved hand slowly along the sidewall to feel any raised area or dent.
- Look for sidewall cuts, deep scuffs, cracking or exposed cord.
- Compare each tyre with its pair. A bulge or a depression in the same place on both sides can show impact damage.
- If you find anything, stop driving the car and arrange replacement.
Also read how to judge general wear in how to know when tyres need replacing.
How a mobile fitter helps
If you find a bulge at home or at work, the safest option is not to drive the car. A mobile technician can attend, remove the damaged tyre, inspect the wheel for bends and fit a new tyre. Our emergency tyre fitting page describes the service, and mobile tyre fitting covers planned replacements. We can also check the other tyres, the valve and the TPMS sensor. See TPMS and valve replacement.
When a tyre is replaced, consider the matching tyre on the same axle. If it is well worn, a pair keeps grip and braking consistent. Our size guide helps you find the correct size from the sidewall.
We cover many towns, including London, Manchester, Glasgow and Bristol. Call now for a quote on 0800 772 0355 or book now.
Other sidewall damage to watch for
- Cuts or gouges reaching the fabric.
- Cracking that goes deep rather than fine surface lines.
- Rubber peeling or separating.
- A dent or flat spot that does not clear after driving.
- Vibration that appears after hitting something.
Any of these merits inspection by a professional. A tyre may still hold air while being unsafe.
Preventing sidewall damage
Keep pressures at the recommended figure, slow down for potholes and speed humps, avoid scraping kerbs when parking, and have tyres checked if you hit something hard. Look at tyres at least once a month in good light.
What a technician checks when replacing a damaged tyre
A bulge usually comes from an impact, so the wheel deserves as much attention as the tyre. The technician checks the rim lip for bends, cracks and gouges, looks for leaks at the bead seat and examines the valve. A bent rim can cause vibration and repeated pressure loss, and a cracked alloy is unsafe. If damage is found, they will explain options before any further work.
It is also wise to compare the age of the tyres. The date code on the sidewall (four digits showing week and year) tells you when the tyre was made. Tyres more than about ten years old are generally best replaced regardless of the tread, since rubber hardens and weakens with age.
Frequently Asked Questions
Can a tyre bulge be repaired?
No. A bulge means internal damage and the tyre must be replaced.
Can I drive a short distance with a bulge?
It is not safe. The tyre can fail without warning. Arrange replacement before driving.
How do I know if it is a bulge or normal tyre shape?
A bulge is a localised raised area, unlike the even curve of the tyre. If unsure, have a technician look.
Can you replace it at my home?
Yes, in most cases. Call now for a quote on 0800 772 0355.
Related Help
Need help with your tyres now?
Call now for a quote, or book now online. Phone 0800 772 0355.