Most 4WDs used for commercial purposes spend the majority of their life on sealed roads with occasional use in rocks, mud, dirt or sandy terrain. Ideally a different type of tyre would be used in each of these situations but practicality dictates that one type of tyre is used to cover all, and where required driving style is adjusted to compensate.
If you look at a tyre where is meets the road, you will notice a flat area where the tyre is deformed. During driving, the flat section of tyre is constantly moving and, as this occurs, heat is generated. If too much heat builds up, the tyre can be damaged and blow out. The lower the tyre pressure, the wider the flat deformed area. The picture below shows the deformation area of an all-terrain tyre inflated to 16 psi at rest on bitumen.
All-terrain tyre with 16 psi pressure showing deformation.
The deformation area can clearly be seen at this pressure. At 16 psi on bitumen road surface, the steering would feel sluggish, there would be obvious tyre noise and most certainly there would be heat build up beyond the tyres normal operating temperature when driving at normal speeds.
Maintaining correct tyre pressure
It is important to maintain the correct tyre pressure for the particular road surface, load and speed. We recommend pressure up to 40 psi when driving on bitumen roads. Pressure this high will reduce the deformation area and generate less heat, which in turn means less rolling resistance, reduced fuel consumption, and less chance of tyre blow out. The downside to high tyre pressure is an increased risk of puncture and an assessment of the road surface should be made before deciding on pressures.
During off road use, it is preferable to have as much contact with the driving surface as practical without compromising the tyre side wall or seal between the tyre and the rim. Lower pressures allow the tyre to mould to the terrain, absorb shocks, maintain traction and reduce the chance of sharp objects causing a puncture. We recommend pressure as low as 24 psi for driving on rocky and muddy surfaces and 18 psi for driving on sand. It is important to make sure the tyre side wall is not compromised when using lower pressures. The picture below shows an all-terrain tyre side wall showing signs of bulge at 16 psi. This effect is magnified when moving over rocks, logs and other uneven surfaces.
All-terrain tyre with 16 psi pressure showing bulge.
Adjusting tyre pressure for driving in mud.
Vista Hire fits your 4WD rental vehicle with tyres suitable for your purpose
Our experience from assessing the wear and damage to tyres after covering millions of kilometres in all sorts of terrain, gives us confidence in the choice of tyres we fit to our rental 4WDs. We fit as standard, all-terrain, 10 ply tyres with reinforced side walls that are recommended for use of 70% on road and sand versus 30% on dirt and mud. If you have a specific requirement or intend to spend an extended amount of time in a particular terrain type, we can advise and fit your rental vehicle with tyres suitable for your purpose. Contact us for more information.