If you’ve driven more than about a mile, friction with the road, flexing of the tire casing and flexing of the tread begins to heat up the air inside the tire.

A very general rule of thumb is that a properly inflated/loaded tire, when up to operating temperature - one hour or more of operation - will typically run about 50 Fahrenheit hotter than the ambient temperature.

Inflation pressure controls the shape of the tire casing. Proper inflation pressure is critical to maintaining proper shape of the tire and proper stress distribution in the tire. This in turn reduces flexing and heat build-up.

The first step as the temperature increases corresponds to the thermal expansion of the air inside the tire, which can lead to a blowout if the structure of the tire is already weakened.

Then, when the tire temperature reaches the initiation of the degradation reactions (pyrolysis and thermo-oxidation), which could be close to 100C, the production of flammable species starts, including gases, which further increase air pressure inside the tire and the risk of blowout.

The final stage takes place when the three critical conditions for an explosion are met, i.e., the auto-ignition temperature and critical concentration of a flammable species, and an oxygen concentration above 5.5%. Such an explosion can occur even after the heat source has been removed, since the chemical reactions involved are highly exothermic. The stopping of the vehicle further increase the risk of explosion since the heated tire is no longer being cooled down by air circulation.

Wants to understand more in details? See below.

Temperature increase may generate three different processes in the tire: air expansion, loss of structural mechanical resistance, and chemical degradation.

1) Air Expansion:
When the temperature inside the tire increases, the pressure inside the tire also increases roughly as below.
- For RV & Truck Tires - Every 10 F = 2 PSI
- For Passenger Car Tires - Every 10 F = 1 PSI

2) Loss of Structural Mechanical resistance:
between 95C and 125C, microstructural changes within vulcanized rubber may create substantial stress relaxation, material softening, permanent set, and creep, which affect the rubber’s mechanical behavior.

3) Thermo-chemical Degradation:
This includes pyrolysis, thermo-oxidation and combustion. All three reactions produce flammable gases.

Pyrolysis takes place in the absence of oxygen under the sole action of heat. Pyrolysis leads to a degradation of the tire’s chemical and mechanical properties, which can occur gradually and whose effects can be cumulative following several overheating events.

Thermo-oxidation takes place when oxygen is present. The signs are practically the same as pyrolysis, except that thermo-oxidation does not occur if inflated with nitrogen. At sufficiently high temperature, oxygen absorption becomes autocatalytic, leading to reaction acceleration.

Pyrolysis starts as low as 185 C. The presence of oxygen in thermo-oxidation reduces temperature it occurs. This temperature is close to the normal service temperature of tire, which is close to 100 C.

In the case of a tire, degradation of the rubber takes place during pyrolysis and thermo-oxidation causing the tire to “age” prematurely.

Those problems could include but not limited to:

1) Overheated brakes

- Locked brakes, excessive braking, defective bearing, etc. can cause the tire temperature to rise dramatically. Check those components if you find temperature in one tire is significantly higher than others.

2) Under-inflation of tires

- Under-inflated tire has bigger footprint and thus has bigger deformation and recovery cycle as tire rotates. More flexing will generate more heat.

3) Overloading or unbalanced loading of vehicles

- Overloading of vehicle can cause the tire to sustain more weight than designed and thus has bigger deformation as tire rotates. This is similar to under-inflation.

- Sometimes a vehicle has an unbalanced load; you may notice that one side of tires may have higher temperature than the other side. Redistribution of the weight will correct it.

4) Mechanical or structural change in the vehicle

- For example, trailer side skirts could limit the air flow around the trailer tire and increase their temperature.

5) Electrical discharges from power lines,
6) Fires,
7) Presence of combustible materials, absorbed fuel or inflammable fluids in the tires.

No. High temperature alarm is fixed to 80C and cannot be user adjusted. This is the level at which tires begin to off gas and true temperature damage begins to occur, it was developed as a result of testing by tire manufacturers. The question you should ask is, why would you want to adjust the temperature warning threshold? Does a customer want to adjust the temperature warning threshold higher so it will not alert the customer until it’s too late to stop the damage to the tire?