When both shoulders of a tyre wear down while the centre holds up better, the cause is the opposite of centre wear: under-inflation. It is the more dangerous of the two pressure faults, and just as easy to fix once spotted.
What's happening
At the correct pressure a tyre sits flat across its width. With too little air, the tyre flattens and collapses slightly in the middle, so the two shoulders press hardest on the road and the centre lifts. The edges then wear faster than the middle, producing the both-edges pattern, the mirror image of the centre wear that over-inflation causes.
Why it's the dangerous one
Under-inflation is worse than over-inflation because a soft tyre flexes and builds heat:
- Heat build-up, which in the worst case leads to a blowout
- More fuel used, from higher rolling resistance
- Vague handling and longer braking
- Both edges wearing out early
That heat risk is why a persistently soft tyre is not just a wear issue but a safety one, particularly at motorway speeds.
The fix
As with centre wear, the cure is correct pressure:
- Find the recommended pressure on the door-pillar placard or in the handbook
- Set the tyres cold with an accurate gauge
- Check monthly and before long trips, per correct tyre pressure
A slow leak can cause under-inflation even with good habits, so a tyre that keeps going soft despite being reset points to a separate fault worth chasing down. A tyre already worn to the limit on the edges needs replacing, with the pressure corrected so the new one lasts.
Telling the patterns apart
The three pressure-and-alignment patterns are quickly separated:
- Both edges worn, under-inflation
- Centre worn, over-inflation
- One edge worn, alignment or camber
A glance across the tread width tells you which conversation to have.
From the workshop: both shoulders going is under-inflation, and it's the one I'd nag people about. A soft tyre gets hot, and hot tyres let go. You'll feel it in the fuel bill too. Thirty seconds with a gauge once a month saves the tyre and a lot worse.
Sources and accuracy. This reflects standard wear diagnosis at the time of writing. The correct pressure for a specific car is given on its placard. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What causes both edges of a tyre to wear?+
Under-inflation. Too little pressure lets the tyre flatten so the two shoulders carry the load while the centre lifts slightly, wearing both edges faster than the middle. It is the mirror image of the centre wear caused by over-inflation.
Is under-inflation dangerous?+
Yes, more so than over-inflation. A soft tyre builds heat as it flexes, which can lead to a blowout, and it uses more fuel and handles vaguely. The wear on both edges is a warning sign that should not be ignored.
How do I tell under-inflation wear from alignment wear?+
Under-inflation wears both edges of the tyre roughly equally; alignment or camber wears just one edge, inner or outer. If both shoulders are going while the centre holds up, it is pressure; if only one, it is alignment.
Does under-inflation affect fuel economy?+
Yes. A soft tyre has more rolling resistance, so the engine works harder and uses more fuel. Keeping tyres at the correct pressure is one of the simplest ways to protect both economy and tyre life.