In the manufacturing process, the tread compound is possibly the most variable, gets a lot of attention from the compound scientists, and is fine-tuned to the application of the product. Mud- and all-terrain tyres that deliver excellent traction, for example, cannot be expected to deliver the tread mileage of a tyre engineered to operate only on paved surfaces.
The tread is just one of the 7-11 compounds that make up a tyre, with each one applicable to a specific task − from holding together the various layers of nylon and polyester, to encasing the bead wires, or ensuring that the sidewall has a specific flexing characteristic. Each compound, in turn, may contain 10-14 ingredients, including various types of rubber (of which up to 60% will be synthetic and produced from petroleum-derived hydrocarbons, while the remaining 40% is derived from the latex tapped from rubber trees).
A key component of most compounds is 25-30% carbon black, used since 1915 to provide a tenfold improvement in the wear-resistance of rubber, to impart the characteristic colour of tyres, and to protect against cracking which comes from exposure to ultraviolet light. Fillers are also vital: a modern development being the use of silica or silica dioxide, used to improve tear resistance. This so-called “coupled silica” is better able to mix with other polymers in the compounds, and enables the forming of tread compounds that are flexible, yet offer low rolling-resistance and good wet-weather performance as they are less prone to heat build-up.
It is worth noting that the road-oriented tyres which have strong levels of performance in the wet, use more silica than carbon black in the compound. Only a few of the higher-end quality 4×4 products offer silica in the compound as this is an expensive additive, but one which will certainly improve your driving experience on- and off-road.
For 4x4ers, another important aspect to consider is the tread depth. Obviously, the greater the tread depth, the longer the tyre is likely to last. On new 4×4 tyres, the tread depths can vary by as much as 60%. You get what you pay for. In off-road situations, a deeper tread pattern will also increase a tyre’s traction, puncture-resistance and durability.
When purchasing your next 4×4 tyre, look at how the tread pattern runs up the sidewall. The more it does, the better. This additional layer is designed to further protect the vulnerable sidewall, and gives greater traction on uneven, rocky or muddy surfaces.
As with all things, the converse is that the more rugged, aggressive tread pattern which is great for mud clearance, grip and traction while off road, is likely to be more noisy on tar, as the deep voids in the pattern create wind disturbance at speed.
In order to get the best from your tyres, particularly when using AT or aggressive MT tyres, they need maintenance. Balancing, rotation and wheel alignment is recommended every 8000km – or more frequently, on a heavier tyre. Regular tyre maintenance of this sort will assist in early identification and corrective action on irregular tyre-wear patterns.
Under-inflation and overloading are still the two major factors in early tyre-failure, so one must check pressures regularly. If you’ve deflated your tyres for the terrain, always re-inflate them as soon as you are on a harder road surface. Under-inflated tyres build up heat more quickly at high speed, and rubber separation caused by overheating will occur. Irreparable damage could be caused, and, as this is happening inside the tyre, you may not be aware of the danger.
By Johann ‘Tyres’ Viljoen, 1st Alignment Centre