SIDEWALL PUNCTURE RESISTANCE AND THE 3-PLY MYTH

By George Shramm, CEO of Tyrelife Solutions

For many off-road enthusiasts, the best way to determine an all-terrain’s puncture resistance is to look at the ply rating. In most cases, consumers view 3-ply tyres as the industry benchmark for off-road use. However, in real terms, ply count isn’t as relevant today as it was 20 years ago. Nonetheless, the perception remains, and, as a result, some tyre manufactures have capitalised on the belief by designing a 3-ply tyre that may not be any more puncture resistant than a 2-ply equivalent.

But how’s that possible? Surely a 3-ply tyre must be stronger than a 2-ply?

Well, yes and no, because there’s more to sidewall puncture resistance than just ply count. In most cases, when a tyre is lost to sidewall damage, it’s generally because the tyre was deflated for off-road use. In these instances, the deflated tyre starts to bulge at the sidewall, thereby exposing the tyre to sticks, sharp stones, broken tree stumps, and possible pinching between the wheel rim and a rock face. The more the tyre bulges, the greater the chance of incurring sidewall damage.

Truth be told, no pneumatic tyre is designed to run at extremely low air pressure, because the sidewall is now forced to carry the weight of the vehicle while climbing over sharp obstacles. And therein lies the problem, because as we all know, a deflated tyre offers superior traction off-road – as well as more comfort (particularly over corrugations), less chance of incurring cut and chip damage, and better puncture resistance over the tread-belt area.

The drawback to these benefits is that the more the tyre is deflated, the greater the likelihood of sidewall bulge (made worse if the vehicle is heavily laden), and therefore the higher the risk of losing the tyre to sidewall damage.

That said, tyres which boast a LT (Light Truck) marking on their sidewall, along with a high payload capacity and heavy-duty carcass construction, are far more likely to maintain their sidewall shape, while resisting the effects of bulging under partially deflated conditions. Ultimately, if sidewall exposure (or bulge) is the leading cause of sidewall damage, then higher carcass strength and load capacity (which are associated with that Light Truck rating) are far more relevant to sidewall puncture resistance than the number of ply cords.

On that note, cord quality also plays a leading role in sidewall puncture resistance. In much the same way that clothing fabric can vary in strength and quality, so too does the quality of nylon cords used by various tyre manufacturers. Take the Cooper A/T3 4S, for example. While it has two nylon plies on its sidewall, the cord is notably stronger than typical nylon cords. Likewise, the steel belt inside the A/T3 4S is manufactured from super-tensile steel, rather than high-tensile steel. Take another example, that of the Cooper S/T MAXX and STT PRO products. Both tyres make use of an angled ply that’s laid at an 8-degree angle. This technology is called ArmorTek3, and although that may sound like marketing speak, in essence the benefits are not that different to using ripstop canvas as opposed to a typical nylon fabric. Simply put, the one tears and punctures a whole lot easier than the other.

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