How does tyre rotation increase air pressure?

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Discussion Overview

The discussion revolves around the phenomenon of increased air pressure in car tyres at high speeds, exploring the underlying mechanisms, including heat generation due to friction and material properties of the tyre. The scope includes conceptual understanding and technical explanations related to physics and engineering principles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that increased friction between the tyre and road surface at high speeds leads to heat generation, which raises the air temperature and pressure inside the tyre.
  • Another participant clarifies that the term "friction" might be misleading, explaining that the bending of the tyre as it rotates generates heat, which is proportional to the wheel's RPM and thus the car's speed.
  • A follow-up question raises whether the flattened contact area of the tyre is necessary for supporting the car's weight and how the increase in RPM correlates with temperature rise due to the contact area.
  • Another participant compares the heating effect to bending a piece of wire, emphasizing that more frequent bending results in more heat, and notes that under-inflated tyres experience greater heating due to larger differences between the round and flat shapes.

Areas of Agreement / Disagreement

Participants express varying perspectives on the mechanisms of heat generation and its effects on tyre pressure, indicating that multiple competing views remain without a consensus on the precise explanations.

Contextual Notes

Some assumptions about the relationship between tyre pressure, temperature, and material properties are not fully explored, and the discussion does not resolve the complexities of how these factors interact under different conditions.

polka129
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the pressure of air inside a car tyre increases when the car is traveled at HIGH SPEEDS?why is this so?my guess is that at high speeds,the friction between the tyre and road surface increases..so kinetic energy is dissipated as heat energy due to friction.this heat is transfers to the inside of the tyre RADIALLY by conduction and consequently the temperature of air increases thereby increasing its pressure because the volume is constant..

am i correct?.

thanks in advance...
 
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Describing it as "friction" is a bit misleading. There is always a "flattened" area of the tire in contact with the road (because the total contact area, times the air pressure, is what supports the weight of the car.) As the wheel turns, each point of the tire has to bend from "round" to "flattened" and back to "round" again. The material of the tire is not perfectly elastic, and the bending generates heat in the tire material. The same amount of heat is generated in each revolution of the wheel, so heat generated per second is proportional to the wheel RPM, or the car's speed.

Some of the heat generated is conducted through the tire to heat up the air inside, increasing the pressure, and the rest is transferred to the air outside the tire.
 
thank you for your reply sir .quite enlightening.however they stimulate me with some more queries,

"There is always a "flattened" area of the tire in contact with the road (because the total contact area, times the air pressure, is what supports the weight of the car.)"-->does the total flat contact area make it necessary for the contacting area of tyre to be FLAT?

and you mean that as the number of RPM increase the temperature increases because the round section that comes in contact with the road EVERY second increases?
 
Like bending a piece of wire... The more often you bend it, the more heat you get.

An under inflated tyre will also have a larger difference (angle) between round and flat. This creates more heat and is the reason an underinflated tyre has a higher probability of a blow out.
 

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