To Blow or Not to Blow

Everything You Never Thought You’d Need to Know About Tyre Pressure

By Peter Rau

The Ancient Wisdom of the Kalahari

There is a question that gets asked more often in the bush than almost any other. More than “are those lions?” and nearly as often as “whose turn is it to make coffee?” That question is: do I let air out of my tyres?

Many years ago, a wise old Kalahari farmer settled this matter for me once and for all. He looked me in the eye and said: “The heaviest load on any car in the sand, is hard tyres.”

Simple. Profound. Completely true to this day.

Sand and Mud: Go Soft or Go Home

When you’re about to enter a sand track or tackle some dunes, let approximately 50% of the air out of your tyres — down to around 1.5 to 1 bar, depending on how heavily loaded your vehicle is. The lighter the vehicle, the lower you can go. If you’re towing a trailer or caravan, those tyres need to come down too. No point in doing half a job.

What you’re doing is increasing your “footprint” on the sand — spreading the vehicle’s weight over a wider surface area, like the difference between walking on the beach in stilettos versus bare feet. One works. One does not.

In extreme cases you can go very low, but not below 0.6 bar. Below that, things get creative in ways you don’t want.

A few important rules for sand driving:

No sharp turns at very low pressure. Your tyre can “debead” — which is the technical term for it climbing off the rim in protest. This is not a good development.

Do not hit the brakes unless absolutely necessary. Braking in sand doesn’t stop you so much as it builds you a very personal wall of sand directly in front of your wheels. Then you’re stuck. Instead, let the vehicle slow itself down naturally. If you’ve already built yourself a sand wall, reverse a little, get some gentle momentum going, and drive over it. Think of it less as an obstacle and more as a suggestion.

This is not a rally. Drive at a safe, sensible speed in 4-wheel drive high. The sand will humble you regardless — there’s no need to help it along.

Watch your pressure throughout the day. Here’s a sneaky one: you deflate to 1.3 bar in the morning and feel very clever about it. But as the day heats up and you’ve been grinding through long sandy stretches, heat builds inside the tyre and that pressure creeps back up — sometimes close to 2 bar again. Suddenly you’re battling the sand and wondering what went wrong. Check your pressure during the day on long sandy routes. The sand hasn’t changed. Your tyres have.

Once you’re safely back on firm ground, pump everything back up to the manufacturer’s specified pressure. Then check it again the next morning — tyres cool overnight and the pressure will drop a little. It’s not trying to inconvenience you. It’s just physics.

Rocky Terrain: The Overripe Tomato Principle

On rocky terrain, there are two schools of thought regarding tyre pressure. The first school says hard. The second school says soft. I am firmly enrolled in the soft school.

There is a saying that it’s very difficult to cut a soft, overripe tomato with a sharp knife. The same logic applies to tyres on rocks. Run them a little softer and they wrap themselves around the edges of the rocks rather than sitting rigidly on top of them, giving you far better grip and control.

However — and this is important — softer tyres mean the sidewalls sit lower and closer to the rocks. Sidewalls are thinner than the tread. A sharp rock edge will cut through a sidewall the way an iceberg introduced itself to the Titanic. We all know how that ended.

So: drive slowly. Be very aware of exactly where your wheels are at all times. Think about what could harm them. The rule is simple — as slow as possible, but as fast as necessary. Rocky terrain rewards patience and punishes impatience in equal measure.

Gravel Roads: The Forgotten Middle Child

Gravel roads are often treated as though they require no special thought — they’re not sand, they’re not rocks, surely they just look after themselves? They do not.

If your vehicle allows it, select 4-wheel drive high on gravel. You’ll have noticeably more control, particularly when things get loose or corrugated. Deflate your tyres by about 15 to 20%, bringing them down to roughly 2 to 1.5 bar depending on your load.

Drive carefully. Be courteous to other road users — flying rocks and dust clouds are unpleasant gifts to leave for the vehicle behind you. And here is a curious fact that nobody has ever satisfactorily explained: the tyre most likely to get a puncture on a gravel road is the left rear. Not the front. Not the right. The left rear. Every time. Why? Nobody knows. The left rear tyre keeps its own counsel on this matter.

Happy travelling. — Peter Rau