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Please tell me the reason in reference of thermodynamics that why pressure in a car tyre increases during driving.

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when we drive , the frictional force between the tires and the road increases the temperature of the air inside the tire.

According to Gay-Lussac's Law,

p ∝ T ; [When volume is constant]

so the increase in temperature also increases tire pressure.

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  • $\begingroup$ But I suppose rubber is non conducting. Atleast not that easily $\endgroup$ – Shashaank Feb 25 '17 at 20:03
  • $\begingroup$ you're right. It takes a real long drive to get changes in pressure in tire. $\endgroup$ – gUUBI Feb 25 '17 at 20:07
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    $\begingroup$ Not that long. 15 to 30 minutes does it. I see it every day, have automatic pressure gauge I see electronically. It may not be proportional to the heat because non conducting for a while, but still easily detectable. Bigger changes from winter to summer $\endgroup$ – Bob Bee Feb 26 '17 at 6:01
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The tyre does heat up, but not because of friction: the tyre does not slide along the road and the friction between tyre and road therefore does no work.

What does happen is that the tyre is not perfectly circular. It is squashed by the weight of the vehicle. As the vehicle moves, the part of the tyre that was squashed moves towards the back of the vehicle, up away from the road, and recovers its shape; and the part of the tyre that was towards the front rolls down to the road surface and is squashed in its turn.

This constant flexing of the rubber is what makes it hot. (In racing cars the tyres are often designed to be slippery and useless when cold, becoming stickier as they get hot).

The hot rubber warms the air inside the tyre. As other answers have said, given a constant volume, this results in an increase in pressure.

If you had steel wheels instead of rubber ones, they would flex much, much less and get much, much less hot.

You can try the "flexing = heat" experiment yourself by taking a nice thick piece of copper wire and bending it back and forth until it breaks. If you immediately touch one of the broken ends you will burn yourself quite nicely.

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During the motion of wheel friction force acts between tyre and wheel which cause the loss energy in form of heat and this heat increases the temperature and kinetic energy of gas molecules increases hence the pressure increase

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When we drive our vehicle, the tyre pressure gets increased by the road. Inside the tyre, the air gets heated up and thus causes expanding of the tyre, due to the high pressure force created by the friction.

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    $\begingroup$ Hi Yui. I've removed the pictures from your answer as I wasn't sure what they contributed. $\endgroup$ – John Rennie Jun 7 at 6:28
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The more you run, the more heated the tire would be. Seen a pressure cooker haven't you? the gas molecules expand (start to move in a larger area). Thus needing a larger are, the pressure increases. This often leads to loss of air because the pressure is high and some amount of air has to escape or else the tire will burst. That is exactly why it is also said, fill lesser air in the tire during summers.

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    $\begingroup$ Your answer goes in the right direction, but there are a few obvious spelling/wording mistakes that you may wish to correct in order to avoid misunderstanding. $\endgroup$ – flaudemus Feb 23 at 20:00

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