Quick answer
A tyre with a visible bulge, lump or sidewall deformation is likely to fail an MOT because it indicates structural damage.
Do not ignore a bulge. The tyre may be at higher risk of sudden failure, especially at speed or under load.
When a tyre bulge can fail MOT
Sidewall bulge
A lump on the tyre sidewall is a serious defect.
Tread distortion
Uneven bulging in the tread area can also be unsafe.
Cord damage suspected
Bulges often mean internal tyre cords are damaged.
Impact damage
Potholes and kerbs can damage the tyre structure.
Visible cracking nearby
Cracks around the bulge increase concern.
Unsafe condition
Any tyre defect affecting safety can fail.
What causes tyre bulges?
Common causes include hitting potholes, kerbing the tyre, driving with low pressure, age-related weakness or previous impact damage.
A bulge usually cannot be repaired safely. The tyre normally needs replacing.
What to check before your MOT
1. Inspect sidewalls
Check both inner and outer sidewalls where visible.
2. Look for lumps
Run your eyes around the tyre for raised areas.
3. Check after potholes
Impact damage may appear after a hard knock.
4. Check tyre pressure
Incorrect pressure can worsen tyre damage.
5. Inspect tread too
Bulges are not the only tyre MOT issue.
6. Replace unsafe tyres
Do not wait for the MOT if a tyre looks unsafe.
What should you do if you find a tyre bulge?
Replace the tyre as soon as possible. A bulge means the tyre structure may be weakened, and continuing to drive can be risky.
If the bulge is large or the tyre looks badly damaged, avoid driving and arrange assistance.
Related tyre and MOT guides
Frequently asked questions
Will a small tyre bulge fail MOT?
Yes, even a small bulge can be treated as structural damage.
Can a tyre bulge be repaired?
Usually no. Replacement is normally required.
Is a tyre bulge dangerous?
Yes, it can increase the risk of tyre failure.
Can potholes cause bulges?
Yes, pothole impacts are a common cause.
Should I drive to the garage?
Only if safe. Severe bulges may need recovery or mobile tyre fitting.
Best next step?
Replace the tyre before the MOT or further driving.