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What is a bulge on a tyre?
A bulge on a tyre is a swelling, usually on the sidewall, caused by the breakage of the internal plies of the casing. Without the support of the plies, at that point the air pressure pushes only the layer of rubber outwards.
You'll recognise it as a rounded or elongated lump, larger or smaller, that wasn't there before. It can appear straight after the impact or some time later.
Why does a bulge form?
A bulge typically forms after an impact: a pothole hit at speed, a kerb struck while manoeuvring, a speed bump, an object in the road. In the impact the sidewall is crushed between the obstacle and the rim and the internal plies can break.
The risk increases when the tyre pressure is too low and with low-profile tyres, which have less rubber between the rim and the obstacle.
Why is a bulge dangerous?
A bulge is dangerous because at that point the tyre no longer has a strong structure: it's held only by the outer rubber. With heat, load and the stresses of driving, the bulge can give way suddenly and the tyre can burst.
A sudden failure, especially at high speed, can make you lose control of the vehicle. That's why a bulge isn't something to "keep an eye on": it needs dealing with straight away. If the tyre has already burst, read tyre blowout.
Can a bulge be repaired?
No, a bulge can't be repaired: the damage affects the tyre's internal structure, not a hole that can be sealed. Neither a repair kit nor a repair by a tyre specialist can restore the broken plies.
The tyre must be replaced. It's good practice to have the rim checked too, as it may have been bent in the impact. Find out more about the general criteria in when can a tyre be repaired.
What should you do if you find a bulge on a tyre?
If you find a bulge, avoid driving and replace the wheel.
- If you notice it while driving, slow down and stop somewhere safe (see how to stay safe).
- If you have a spare wheel or space-saver, fit it in place of the damaged wheel, or get someone to help you.
- Don't use the repair kit: it's no use for this type of damage.
- Have the tyre replaced and the rim checked.
How can you prevent bulges?
Bulges are prevented above all by keeping the correct pressure and approaching obstacles with care.
- Check the pressure regularly, at the values specified by the manufacturer.
- Slow down before potholes, speed bumps, rails and road joints.
- When parking, don't hit or "climb" the kerb with the tyre sidewall.
- After a hard impact, check the tyre sidewalls, in the following days too.
Bulge on a tyre in Milan?
If you find a bulge on a tyre in Milan or the surrounding province and don't want to drive in that condition, SOS Tyre reaches your vehicle in 30 minutes on average, 24/7: we can fit your spare wheel and agree on the phone, depending on size and availability, the supply of a new tyre. Call +39 377 326 0999 or see our wheel change service.
Frequently asked questions
Is a small bulge on the sidewall still dangerous?
Yes. The size of the bulge doesn't indicate how serious the damage is: even a small swelling shows that the internal plies are broken. The tyre can fail without warning, so it must be replaced just like a larger bulge.
Can I drive home with a bulge on the tyre?
It's not advisable. The bulge can give way suddenly, especially at sustained speed or with a loaded vehicle. If you have a spare wheel, fit it; otherwise stay safely where you are and ask for assistance rather than making the journey on the damaged tyre.
Can the bulge appear days after the impact?
Yes, it can happen. The damage to the plies occurs at the moment of impact, but the swelling may only become visible later, with use. That's why after hitting a pothole hard or striking a kerb it's worth checking the sidewalls in the following days too.
What's the difference between a bulge and ripples in the sidewall?
Some tyres can have slight regular ripples on the sidewall, due to the ply joins made during manufacture; these are indentations, not protrusions. A bulge, on the other hand, is a localised outward swelling. If in doubt, have the tyre checked by a technician.
With a bulge, should the rim be checked too?
It's advisable. The impact that broke the tyre's plies may also have bent or cracked the edge of the rim. A damaged rim can cause air leaks or vibrations even with a new tyre, so it should be checked during the replacement.