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It's tire pressure time! At least when looking at the recent new questions.

So here is another question about air pressure.

At driving schools, shops and in the internet you often find this type of images:

enter image description here

  • The left tire has the correct pressure, the entire tread touches the ground.
  • In the middle, air pressure is too low. The car stand on the edges of the tire and if driving too long, the tread will wear on that edges.
  • The right tire has too much pressure and only the middle of the tread touches the ground. Again, driving too long will cause wear in the middle of the tread.

While I agree with the first two points, I wonder a little about the last. I can imagine this for bias tires, but today, we have radial tires on all cars and most other vehicles. These usually have a circumferential steel belt beneath the tread which does not allow much radial expansion. I think a radial tire with too much pressure still looks more like the first one.

So: Is it still the case that over-filled tires show increased wear in the middle, or is more a popular belief from history, where we had more bias tires?

  • Excellent question! – Zaid Jan 8 '16 at 10:14
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    Surely if you think you can wear the edges if under-inflated, then you could wear the middle if over-inflated. I have seen tires worn more in the middle and would put it down to over-inflation. – HandyHowie Jan 8 '16 at 12:20
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The answer is simple: depends. It depends on the manufacturer's choices in how they reinforce the sidewall and how that is tied in to the belts under the tread.

One should not expect an off-road tire (made for off-road use at low pressure and on-road use at nominal pressure), a wide and low ultra-high-performance tire, and a tall, high profile standard passenger tire to exhibit exactly the same properties when under or over inflated.

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