Before considering how heat affects tyres, it’s worth noting how heat affects people. Most people can stay in a 70 degree sauna for five minutes. Staying in a 70 degree sauna for five hours would be deadly. The impact of heat builds up over time. So the longer a vehicle is on the road, the greater the effect of heat on the tyres.
That’s one reason fleet management is such a challenge in the Middle East; vehicles must spend prolonged periods on the road, in some of the world’s hottest temperatures. This could bring extreme changes to the tyres.
For every one degree change in temperature, tyre pressure changes by 0.19 PSI. Hot weather increases tyre pressure and puts tyres at risk of over inflation. This is especially true when the tyres are inflated early in the morning, when the outside temperature is much lower than in the middle of the afternoon.
Direct sunlight also influences tyre pressure, sometimes making up to a 15% difference in pressure. Black tyres absorb heat and this is passed onto the air inside. Not all your tyres are exposed to the sun. Those on the inside of a dual tyre set up won’t expand, yet those on the outside probably will. Studies on budget tyres have shown that their air pressure increases around 1 PSI for every five minutes spent in direct sunlight.
A tyre flexes when it rotates. This creates friction between molecules in the tyres, which is converted to heat. Heat is also generated through the friction between a tyre and the road. This isn’t a challenge in normal daily temperatures. However, increase the on-road temperature and this heat generation presents serious problems.
The tyres can quickly build pressure and overheat, leading to blowouts. If it’s hot enough to fry an egg on the bonnet of a truck, then the heat could make your tyres explode. Blistering is another common problem caused due to excessive heat generation in the tyres.
Pressure changes and heat generation create uneven resistance from the tyre. Rather than rolling evenly, the tyres start to develop bulges and imperfections. This isn’t immediately dangerous. However, tyres that are unable to dissipate heat will slowly show signs of uneven wear. This reduces the lifespan of a tyre and impacts on the safety of the vehicle.
Friction and heat generation must be overcome in order for any tyre to rotate. Every extra degree in heat increases the rolling resistance. That means you must use more fuel to keep the vehicle moving forward. You won’t notice the difference in a recreational vehicle on a short drive. But for a fleet of heavy duty vehicles spending all day on the road? The increased rolling resistance can mean spending hundreds of thousands more on fuel over a year.