Bulge in a tire sidewall: stop driving on it

Stop driving on that tire. A bulge or bubble in the sidewall means the cords inside the tire have broken, the air is now being held by rubber alone, and it can burst without any further warning.

It cannot be repaired. Not by us, not by anyone, at any price. The tire has to be replaced.

What you are actually looking at

The sidewall is not solid rubber. Inside it there are fabric cords running from the bead up and over to the other side, and they are what carry the air pressure and the weight of the car. The rubber is a skin over the top of them.

When a wheel drops hard into a pothole or strikes a kerb, the tire is pinched between the road and the rim for an instant. That pinch can snap a band of those cords. Nothing shows on the outside at the time. The broken section can no longer resist the pressure inside, so over the following days or weeks the rubber pushes outward into a blister, roughly the size of a thumb or an egg.

Tire manufacturers describe a sidewall bulge as damaged cords from a severe impact, often with a visible break in the inner liner. Their instruction, and ours, is replacement.

The impact may have been weeks ago, and people often remember no pothole at all. That is normal, and it does not change the answer.

Telling a real bulge from normal sidewall shape

Not every irregularity means a broken tire, and nobody should be frightened into buying one they do not need.

Normal and harmless: a gentle wave running around the sidewall, most visible in low light, often just above the rim. That is the overlap in the fabric plies showing through, and it has been there since the tire was made. It is smooth, symmetrical, and goes all the way around.

Not normal: a distinct, local dome standing proud of the rubber around it, in one place only. Run your palm across it and you feel it rise and fall. Sight along the sidewall at eye level and it breaks the line.

If you are unsure, compare the same spot on the tire on the other side of the car. Manufacturing waves appear on both. Impact damage appears on one.

Can you drive it anywhere at all?

Treat the car as immobile.

A bulged sidewall is already failing. There is no speed slow enough to make it safe. If it lets go while you are moving, a front tire takes your steering with it and a rear tire takes the back of the car sideways.

If you have a spare, fit it and keep within the limits on the spare's own label. Read how far you can drive on a donut spare first. If you have no spare, flat tire with no spare covers the real options.

Moving the car a few feet on a driveway to give a technician room is fine. Driving to a tire shop is not.

Why a repair is impossible

The repair standard published by the US Tire Manufacturers Association limits repairs to the tread area, to damage no larger than a quarter of an inch, and requires the tire to come off the wheel for an internal inspection, with a plug and a patch as the only correct fix.

A sidewall fails every one of those conditions. The damage is outside the repairable area, it is structural rather than a hole, and the sidewall flexes on every single rotation so no patch would stay bonded to it. Anyone offering to fix a sidewall bulge is selling you something dangerous.

What replacement involves

We come to the car where it is parked, supply the tire matched to your vehicle placard, fit it, balance it and torque the wheel. That is the point of a mobile service here: the car cannot safely be driven to a shop, so the shop comes to it.

Two things worth knowing before you book. First, check the other tires while you are down there, because one pothole often catches two wheels on the same side. Second, check the wheel itself. The same impact that broke the cords can bend the rim, and a bent rim leaks slowly afterwards.

To find the size you need, use find your tire size. To work out whether one tire or more, use how many tires do I need, which matters on all-wheel drive.

Questions people ask

• Can a sidewall bulge be repaired or patched? No. Sidewall damage is outside the repairable area in every industry standard, and the sidewall flexes constantly so no patch will hold. The tire must be replaced.
• How long can I drive on a tire with a sidewall bulge? Treat it as zero. A bulge is a tire already in the process of failing, and it can burst at any speed with no further warning.
• What causes a bulge in a tire sidewall? Almost always an impact: a pothole, a kerb strike, or hitting road debris. The impact pinches the tire against the rim and snaps the internal cords. The bulge appears later.
• Is it covered by warranty? Impact damage is a road hazard, not a manufacturing defect, so it is normally not covered unless the tire brand includes road hazard cover. We tell you before you buy which brands do.
• Should I replace the tire on the other side too? Not automatically. It depends on how much tread the remaining tire has and on the drivetrain. On all-wheel drive the tolerances are tight enough that it often does mean a pair.
• I have a lump but the tire holds air fine. Is it still urgent? Yes. Holding air is not the test. The cords that carry the load are broken and the rubber alone is doing a job it was not designed for.