Where the Rubber Meets the Road

Words by Scott Brady. Photographs by Chris Collard. Words by Scott Brady. Photographs by Chris Collard.

During the last few years, we’ve forged a great relationship with the folks at Overland Journal − a USbased but internationally recognised off-road publication. Recently, the team at Overland Journal conducted an in-depth comparison test of several all-terrain tyres; the feature was published in their Summer 2014 issue, but they graciously offered us the same review. Go to www.overlandjournal.com to find out more.

In nearly three circumnavigations of the globe and hundreds of thousands of overland miles, I have never had a puncture − not a single tyre flattened by rock, stick, screw, or nail. This is not to say I have not experienced a flat or two, but it has usually been in sand dunes (a lost bead) while running very low air pressure. This does not necessarily merit bragging rights, as I have been entirely bemused by my luck. However, is it luck, or have variables contributed to my good fortune? There are critical factors that influence a tyre’s puncture-resistance and tractive performance. For this comprehensive review, we will expose the side-by-side results of seven leading all-terrains.

TYRE PERFORMANCE FOR OVERLAND TRAVEL
While reliability is arguably the greatest consideration for an adventure driver, I would submit that performance shares an equally critical role. During earlier travels, my thoughts were drawn towards how my equipment would hold up. However, those concerns have since been partially replaced with a focus on how the gear will perform. This applies not only to my vehicle and various modifications, but also to my tyres. They must be durable, reliable, and work really well when things go sideways.

From a romantic viewpoint, overland travel is a series of endless, remote, dirt roads. However, we all know that long sections of tar and graded gravel separate us from those majestic backcountry photo opportunities. For example, a trek to Nordkapp, Norway, would be nearly all tar, but odds are good that it would be snowy or wet tar. For this reason, an all-terrain is typically the best option for transcontinental travel.

All-terrain tread-designs offer reasonable performance for many scenarios, and are very effective for those long transit stages on tar. Evaluating a tyre’s performance is multifaceted and complex, with aesthetics rarely far from the bottom of things to consider. A puncture is typically no more than a minor inconvenience, but rounding a corner at speed and hitting ice or wet tar could be a trip-ending event. Performance influences safety, and this evaluation focuses on how effective a tyre is when we need it most.

TREAD DESIGN
All-terrain tyre development has gone through a renaissance in recent years. The use of computer-aided design (CAD), finite element analysis (FEA), and advanced rubber compounds have resulted in exponential improvements. As a result, it is possible for all-terrains not only to look great, but also to perform effectively on- and off-road. Tread design has a significant influence on traction, with components including lug void space, lug shoulder shape, siping, and lug integrity. Void space primarily assists in the evacuation of mud, snow, and water, and allows the lug face to present a clean biting surface on the next revolution. The shape of the lug and void space contributes to how the tyre holds a line in mud and snow. Interrupted void channels improve slope-holding (lateral slip) for a cambered sidehill and down / uphill in mud and snow, but reduce the effectiveness of water evacuation. The angle of the lug shoulder contributes to stone retention and lug integrity. An angled shoulder will help reduce stone-retention and tearing and chunking of the rubber.

Sipes are thin slits in the face of the lugs. They provide additional biting edges on the contact patch and significantly improve wet surface and snow / ice traction. The effectiveness of these hairline cuts should not be undervalued, as they affect mechanical keying (defined below) as well as increasing traction on other surfaces. However, siping can produce compromises, which include accelerated wear and tear of the rubber. There are pros and cons to siping, but the trade-offs are worth it.

GLOSSARY OF TERMS
Adhesion

Adhesion is realised during the period of contact between the tread and the tractive surface. It is most relevant on dry surfaces, and diminishes rapidly once moisture (as frozen or liquid water) is introduced. A tyre’s rubber compound, which is a cocktail of natural and / or synthetic rubber, carbon black, silica, sulphur, and other agents, has a great influence on adhesion. For example, when driving on Moab’s slickrock, how well a tyre “sticks” to the terrain is a property of adhesion. The same applies onroad, where effective adhesion improves grip while cornering, braking, and accelerating. With racing tyres for roads, such as those used in Formula 1, the focus is on maximising the tyre-totrack adhesion and micro keying.

However, tyre manufacturers have been hard at work perfecting their rubber-carbon-silica formulas, and most currently use a proprietary compound. For example, Falken drew on their years of experience with high-performance racing tyres when they engineered the WildPeak rubber, with impressive results.

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