Lorry tyres are inflated to a much higher pressure than car tyres – between 80-110psi vs 27-40psi. When they are inflated, it’s done with the tyre in a cage which protects the person filling it if it blows.
A tyre is likely to blow if it develops a weakness in the sidewall (the thinnest part of the tyre) or it receives an impact that exceeds the pressure the sidewall can cope with (e.g. running up a kerb at speed). It’s not likely to blow due to a nail or screw in the tread, it’s more likely to go flat slowly or, at least, without a big bang. The sidewall could have a weakness due to:
- a manufacturing default
- an impact caused by a pothole
- something rubbing on the tyre
When a lorry tyre blows, it can damage anything in the immediate vicinity – the mudguard, air and brake lines, wheel rim and bodywork. A blowout is different to a delamination. A delamination is where a retreaded tyre comes apart and it can leave large chunks of rubber (or even a whole tyre carcass) lying in the road. As it disintegrates, bits of it fly out behind the lorry as they are thrown due to the rotation of the wheel.
A blowout can still have this kind of degradation and tyre breakup but the driver is much more likely to notice:
- blowouts are noisy – like a gunshot
- blowouts instantly change the feel of the lorry if they are on the front wheels or the drive wheels, whereas slow punctures are gradual
It should be noted that a blowout on a trailer with multiple wheels would be much more difficult to notice, especially if the truck is already noisy and hides the noise of the blowout.
So, you have a tyre that has blown out. What can happen then (but doesn’t always happen) is that the loose bits of the tyre begin flailing around with the rotation of the tyre. Eventually, if the driver doesn’t notice, the stresses and strains on the tyre become too much and it begins to break up, discarding big chunks behind it and eventually significant chunks until there’s not much left of the treaded part on the rim.
As mentioned, if the front tyre deflates it’s easier for the driver to notice because the steering will be much heavier and the lorry will pull towards the direction of the blowout. The driver must stop the truck quickly otherwise the rim could be damaged.
If a drive wheel has a blowout, it will likely be audible to the driver but if there are four wheels on that axle it might not change how the lorry feels to drive.
If a trailer wheel has a blowout and there are four wheels on the axle, it’s less likely the driver will feel it. There is a risk of overloading the tyre on the axle. In harsh cornering, there’s more likelihood of the trailer tipping on the side of the blowout.
Darren has owned several companies in the automotive, advertising and education industries. He has run driving theory educational websites since 2010.