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Updated: Apr 29, 2020

Cooper ST Maxx / SA Adventure

In June we spoke about All-Terrains (Thick & Thin), and focused on a crucial fact about Passenger and LT tyres. Essentially, the story highlighted the strength and rubber differences between the two tyre types – despite the fact that the tyres are identical in every other way.

This month, we’re looking at sidewall ratings, and the longstanding myth that ply count is the be-all and end-all of tyre durability.

There’s no contesting that a 3-ply sidewall will be stronger than a 2-ply sidewall – provided the two tyres are precisely the same in every other way. Unfortunately, because of age-old misconceptions and misleading marketing, off-road tyre buyers have been led to believe that the only aspect worth considering is the number of plies across the sidewall. In the process, a fundamental feature of tyre design has fallen by the wayside: the BULK.

Perhaps the best way to explain this is to think of steel versus kevlar. Sure, the latter is incredibly strong for its weight, but there’s a reason why armoured vehicles are made from hot-rolled, thick steel… and the same applies to tyre design. Although ply ratings are important, an equally vital consideration can be found in basic tyre construction, rubber density and overall thickness.

Take the Cooper Discoverer S/T Maxx as an example; this particular tyre features a 3-ply sidewall rating, along with ArmorTek3 technology. (More about this in a later article). More importantly, the Maxx boasts a phenomenally robust sidewall construction. In fact, it’s unquestionably the toughest off-road commercial tyre that Cooper has ever built.

This leads us to the burning question: how do you know if a tyre is robustly (thickly) constructed? Well, in the case of our off-road and LT tyre range, you’ll find a Load Range Letter written on the tyre’s sidewall. This alphabetical symbol equates tyre thickness to a comparable ply rating. For example, the letter “E” written on the side of a 265 / 65 / R17 S/T Maxx tyre, suggests that the comparable sidewall rating would equate to a 10 ply. In most cases, our off-road tyres are either a C (6-ply), D (8-ply), or E (10-ply) rating.

Alternatively, if you’re looking for a more anecdotal approach to gauging a tyre’s carcass construction, the easy way to do it is: simply pick the tyre up and feel its weight. Coming back to our Cooper S/T Maxx example; if you compare the weight of this tyre against a close competitor and well-known off-road tyre brand, you’ll find that, size for size, (using a 31x10.5x15 as an example) the Maxx weighs in at 22.7kg, while a leading competitor tops the scale at 20.7kg. (10% more rubber for the S/T Maxx)

So if you’re in the market for a new set of tyres, and you specifically want durability to feature high on the list of qualities, excuse the pun, and “weigh up” your options.

Click here for more information on the S/T Maxx.

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