Five common misconceptions when it comes to 4WD tyre pressures.
Myth #1: Skinny tyres are better than wide ones for sand driving.
This is perhaps the easiest one to dispel quickly. Just ask whoever is telling you this to go ride their 10-speed bicycle across soft sand.
I’ve had guys try to rationalise that skinny tyres get longer, while wide tyres get wider. In the real world, they both act almost identically, with each tyre’s contact patch inversely linear with its pressure.
Basically, if you’re starting out with a bigger tyre, when you pressure down, you’re ending up with a bigger tyre. And when it comes to flotation on sand, bigger is better.
Myth #2: Higher pressures are better for mud driving.
You can see where this one comes from: a lot of farmers running narrow split rims on their utes in muddy farm tracks. With low pressures, they lose clearance and get stuck.
Most modern 4WD fitouts (not from the factory) will include some kind of suspension lift, as well as larger diameter tyres, which means that clearance is less of an issue than traction.
And aired down tyres will provide more traction in mud because there is, simply, more surface area, and more surface area means more friction. It’s just physics.
Myth #3: Below 20psi you’ll run your tyres off the bead!
We’ve been lucky enough to experiment with a wide range of tyre sizes and pressures in the field. We’ve also been unlucky enough to find out where the limits lie when it comes to low pressures and losing the bead on rims.
With low profile tyres, airing down below 20 psi can be dangerous, especially when it comes to turning hard, doubly so with the front wheels.
But with offroad tyres (we’re generally running something like 275/65R16 tyres), you can go much lower without high risk.
I’ve personally taken my 100 Series towing across the Simpson Desert at 10psi the whole way with zero issues.
What you have to remember is that psi is pounds per square inch (long live the imperial system!)…and the more square inches you have, the more pressure you have, even at a lower psi.
This is one of the most important, and not terribly intuitive, reasons that we run tyres with larger sidewalls.
Myth #4: Lowering your pressure on gravel roads exposes your sidewalls and is a bad idea.
They say that in every myth or legend is a kernel of truth. Way back in the olden days, before we had modern tyre rubber compounds and radials built for offroad use, this was perhaps true.
Today, I see it more as an educated wager. Lower pressures generally introduce higher temperatures, along with a degree of increased exposure for the sidewalls to stone cuts, etc.
But modern tyres are much more durable than their ancestors, so the sidewall problem isn’t as acute as it once was. And more importantly, tyres are not the most expensive part of your 4WD. They are, and should be in some ways, expendable, a fuse between the world and everything else on the vehicle.
Lower pressures let the tyres become part of the suspension system, reducing wear and tear on the suspension, drive train and every single nut and bolt on the 4WD, nevermind your own nerves and joints.
Yes, you’ll wear them out a little faster, but as they say, it’s not the years it’s the mileage…and if you can reduce the damage to your 4WD from every kilometre, you’re going to save more than the cost of tyres in the long run.
Myth #5: Don’t let your pressures down for rocks, you’ll puncture the sidewall!
Unless you’re driving recklessly (in that case, you probably aren’t reading this), lower pressures actually help your tyres to conform to the rocks you’re driving over.
More than that, it helps you maintain traction. Most sidewall slices I’ve seen have come from tyres slipping or spinning against sharp rocks when they’ve lost traction.