A few days ago, the UK Met Office issued its first ever red warning for extreme heat, and there’s a fair chance that today or tomorrow, temperature records will tumble.
Road travel is likely to be unpleasant, and maybe even dangerous if you get stuck for hours in traffic. In some local authorities, gritters are out spreading sand on roads, in an attempt to stop the tarmac melting. It all sounds like the sort of thing you’d expect in Texas, not here in rainy old Blighty.
So, what does all this mean for your tyres, and should you be worried?
Heatwaves are bad news for tyres
The biggest problem heatwaves pose for your tyres is increased tyre pressure. As the temperature rises, so does the pressure inside your tyre.
We’ve know for a couple of hundred years that the volume of any gas increases in proportion to its temperature (Charles’s Law). That’s because at higher temperatures, the gas molecules are zipping around faster. On average they’re further apart, so the gas takes up more space. However, if you keep the gas confined to the same volume —inside a tyre for example — the gas pressure goes up instead.
Given that tyres are designed to operate within a certain range of pressures, it’s possible that high temperatures can push the tyre beyond its limits, resulting in a catastrophic failure.
Let’s put some numbers on this. Helpfully, Wikipedia provides a cold inflation table which covers a wide range of pressures and temperatures for tyres.
It turns out that a tyre that’s inflated to 30 psi at 20 centigrade will increase to 31.5 psi at 30 C. By 40 C, it hits 33.2 psi.
This may seem a fairly modest increase, but it can be enough to push a tyre from ‘correctly inflated’ to ‘over-inflated’.
Now add hot, sticky tarmac
Increased air temperature isnt the only source of stress your tyres have to deal with in extreme heat. There’s also the road surface. As the tarmac heats up, some of that heat will be transferred to the air in your tyres, further increasing the pressure. The tarmac gets stickier too, which increases friction between the tyre and the road surface. This leads to — you guessed it —higher temperatures and pressures inside the tyre.
So, will your tyres explode?
Whether your tyres fail because of the heat is going to depend on several factors:
- the age of your tyres
- the condition of your tyres
- how long they’re exposed to extreme temperatures
- how inflated they were to begin with
- How long they’ve been at their current pressure
You can see how this works. If your tyres are getting on in age, you’ve left them standing in one position for months, they’ve already been over-inflated for some time and you’ll be driving in high temperatures for many hours andthe risks of a failure start mounting up.
On the other hand, if you’ve got newish tyres in good nick, you’re on a shorter trip and they were correctly inflated to start off with, the risks are much lower.
However, like most things in life, there are no guarantees.
Lowering your risk of tyre failure
The obvious way to lower your risk of a blow-out in very hot weather is to check your tyres’ condition and pressure before a significant journey. If the tyre pressure is above where it should be, you can cautiously let some out so that it’s back in line with manufacturer recommendations. But if you do this, you must remember to check the pressure next time you start out. Otherwise you might end up driving on a dangerously under-inflated tyre.
To answer our earlier question, the current heatwave shouldn’t have you panicking about your tyres. However, you should definitely take some straightforward extra precautions.
The BK Tyres blog covers a wide range of topics related to tyres and driving.