Don’t drive under pressure

Save lives on the road


There are some basic things we need to understand about a tyre before we go into the technical realities of running tyres in a modern trucking fleet. The tyre is the only connection between the truck and the ground, and the medium which is holding the truck off the ground is, in fact, the air within it. Tyres are a very important component in any trucking operation, coming third behind wages and fuel in terms of costs.

Not only does the tyre hold the truck up from the ground, it is also an important safety feature, keeping the truck in a straight line and enabling it to go around corners safely. It is also vital that it has the correct friction coefficient to stop the truck in an emergency. The air in the tyre also has the effect of reducing vibration and noise from the road entering the truck and improving ride both for the driver and for the freight.

Tyre pressure is a very important factor in the performance any tyre. With the kinds of masses truck tyres are carrying it becomes an even more important factor, truck tyres are bigger and contain more air, so pressures become more critical. Tyre pressure has a direct effect on the tyre’s overall performance, fuel economy and the life of the tyre. When looking at truck tyres, studies have shown that more than 80 per cent of tyre problems are caused by under inflation.

The problem is there are no fixed rules on what is the right tyre pressure for each individual tyre in any particular situation, it depends upon the load the truck is carrying, the speed the truck is travelling at and the conditions of the road itself.

Tyre manufacturers do provide load and pressure tables, but operators will tend to err on the side of caution and run at higher pressures than would be ideal. Also, if tyres are running at too high pressure and not getting checked, they are less likely to be running at less than ideal pressures. Running a tyre at a higher than ideal pressure does cause some problems and can lead to uneven wear in the tyre. Over-pressure tyres get three times the punctures, stone bruises, cuts and uneven wear. They cause damage to suspension, drive line, roads and trucks, thus increasing maintenance costs and break downs.

Checking the pressure

Simply finding out what the correct tyre pressure is can also be an issue. The inflation pressures shown by by most airlines in service stations are wildly inaccurate. Even hand held tyre pressure gauges can be unreliable, especially if not checked regularly.

Just checking all of the tyre pressures on something like a B-double set can be quite a task. Not only are there all of those tyres, but many of them can also be hard to get at, especially the inner tyres on dual tyre axles. It is often a chore which a driver knows they have to do, but quite often feel they don’t have enough time to get the job done properly and don’t do it themselves. If the tyre pressures aren’t checked regularly, the operator can be certain there will be disparity in pressures across the vehicle.

How do you know the what the right pressure is?

Some tyre users can find the correct tyre pressure for their vehicle using the 4psi rule. This entails setting the tyre pressure at a point you think it should be set at and then running the vehicle for 100 km. The pressure needs to be checked again and if the tyre pressure reading is more than 4 psi above the original pressure the starting tyre pressure was too low. If the tyre pressure reading is less than 4 psi above the original tyre pressure, the original tyre pressure was too high. If the tyre increases in pressure by 4 psi, the pressure was just right. Running this experiment a few times should enable you to get the right pressure for your vehicle. If the truck is running on dirt roads then the rule becomes the 6 psi rule.