The subject of tyre deflation is surprisingly contentious; folks seldom agree on figures, and in some cases I’ve even heard 4×4 training academies arguing that you shouldn’t do it! But before we get into that, here are the top 4 reasons why you should:
3) THE ENVIRONMENT
4) SPORTS BRAS
Let me explain…
DO OR DIE:
Admittedly, that heading’s a bit dramatic; but (before you roll your eyes) here’s the formula: Deflation = Traction = Control = Safety = Not Dying. Pure science. To be clear – and here’s where some confusion creeps in – we’re not looking to increase the bulge / width of the tyre, but rather to stretch out the tread length.
Another contentious issue is the subject of air pressure, and knowing what the best figure is for each terrain type. But that’s like me telling you how many beers you can drink before your face hits the floor. (It all depends on how big you are, and what your tolerance level may be….) Likewise, the pressure all depends on how heavy your vehicle is, what your driving skills are, and what size and type of tyre you use.
For example: An LT tyre will require more deflation than an OE fitted all-terrain. Bigger tyres will also need more deflation (because they’re made with more rubber), and similarly, a 3-ply tyre will need more deflation than a 2-ply tyre. In other words: what one tyre does at 1.3 bar is completely different to what another tyre will do at the same pressure.
This matter is further complicated by the infinitely vast number of terrain types available; sand alone can vary in texture, granule size, depth, moisture, temperature, and more. However, the point to remember is that a deflated tyre dramatically improves off-road traction, performance, and control. As far as I’m concerned, that’s reason enough always to do it; everything after this point is simply a bonus.
Not long ago, a well-known 4×4 publication in Australia (4WD Action) conducted a puncture-resistance test. They hoped to evaluate the difference between tyre types (their construction), as well as the relationship between air pressure and puncture resistance.
Their test was conducted using three types of tyre: a stock HT tyre, a Cooper AT3, and the Cooper S/T Maxx − an incredibly tough all-terrain that’s used on production-class rally cars, but also commonly used by avid off-roaders.
Their test involved driving each tyre (fitted to a Hilux 4×4) over a steel spike. They recorded how many times the tyre could roll over the spike before it was punctured. However, they also performed this test at varying tyre pressures. Here are the results of that test:
As you can see, the factory-fitted HT tyre didn’t do very well, even when deflated to 1.4 bar. More important, however, is the incredible result of what a true off-road tyre can do when deflated. The S/T Maxx shouldered 24 rollovers (at 1.0 bar) before a puncture occurred. Meaning: the S/T Maxx was 12 times more puncture resistant than the (un-deflated) stock HT tyre! If you’re still wondering if you should replace your HTs for a set of bonafide off-road tyres, perhaps this info will help.
Unfortunately, not everyone’s concern, but the fact is that a deflated tyre is far less harmful to the environment. The benefits are twofold: One, a deflated tyre offers more traction, which means that it’s far less likely to spin and cause damage to the trail. Two, a deflated tyre is able to mould itself to the contours of the terrain. And what’s more, a deflated tyre has more contact with the terrain, and this in turn reduces the forces on the terrain per square centimetre.
An obscure point, but one that refers to the increased comfort a deflated tyre provides off-road. Needless to say, the weight of your vehicle is carried by the air in your tyres, and the more air you let out, the greater the weight transfer (as well as movement and flex) to the tyre itself. The upside to this is that the tyre provides an extra “suspension” effect and increased ride comfort to your 4×4 off-road. (It also reduces the level of vibration through your vehicle, and therefore, the chances of picking up a rattle or squeak.)
The downside, is that the air is no longer carrying the bulk of the vehicle’s weight, and more stress (along with potential damage) is being transferred to the tyre − which is why so many tyre manufacturers are dead-against ANY degree of tyre deflation. Some dedicated off-road brands (such as Cooper) are more accepting of the need, but their concern is directed more towards extreme under-inflation, or, driving a deflated tyre at speed.
SO WHAT IS THE RIGHT PRESSURE?
Unfortunately, there’s no straightforward answer to this question, as no two vehicles are alike; also, there are terrain variations to consider, and the fact that tyre construction vastly varies from one manufacturer to the next. The table below offers a rough guide to deflation percentages, but (in the end) it’s really a dark art that every off-roader must master, a process of trial and error that starts and ends with each track.
By Grant Spolander