Fundamentals

TYRE PRESSURES FOR 4WDING

Shauno’s tyre pressure trips for mastering driving on the beach, 4WDing in mud & all sorts of terrain! You might be surprised to hear that Shauno’s ultimate off-road mod to save you from getting bogged is NOT a diff lock! Shauno compares 40psi vs 20psi vs 15psi and puts these tyre pressures to the test.

Shauno tyre pressure

You probably think that maybe diff locks, bigger tyres and suspension lifts and reduction gears are the top ways to avoid getting stuck and bogged – but if you are thinking these things, you are wrong. Even a humble little stick can be more important, because we are talking about the importance of your off-road tyre pressures, and just a small twig can let down your tyre pressures and help you get further off road.

Obviously, tyre deflators come in much more sophisticated versions than a stick - like quick deflators and multi-tyre deflators – but a stick will do the trick to get those tyres down to operating levels that allow you to drive tough terrains without getting stuck.

TYRE PRESSURE TEST

We put tyre pressures to an ultimate challenge to scientifically find out what tyre pressures (PSI) should be used in what terrain. We tested a series of 4WDing challenges, from dirt, corrugated ruts, sand, to mud and dirt.

40 vs 20 vs 15 PSI

We figured the best way to demonstrate the difference between road pressures compared to off road tyre pressure is by painting the tread of our tyre at different pressures and lowering it onto a piece of cardboard to visibly see the difference in the tyre footprint.

tyre footprint40psi - Highway Pressures

Breaking down the results here, you would probably be surprised that at 40psi there is not much rubber in contact with the ground – and you would be right! For a tyre this size, that is a very small contact point. This really shows why we put our tyre pressure down and how it makes a huge difference off road.

20psi - Standard 4WD Pressures

At 20psi we can see that there is a lot more rubber in contact with the ground, but in particular, pay attention to the length of the footprint: 210mm vs 170mm. The widths of the tyre at these pressures are similar but the extra length of your tyre’s footprint at 20psi is what gives you a huge advantage while 4WDing.

Imagine dropping your tyre pressures even lower, down to 15psi or even 10psi, this contact point would be even greater in size and give you incredibly more traction offroad.

FOOTPRINT LENGTH

A good way to appreciate what happens to your tyres when you deflate them for 4WDing is to look at an exaggerated example like a tractor. Tractors have a small front tyre and a large rear trye and almost never get bogged. It is not necessarily the width or thickness of a tyre that is important, but more the length of the tread that that is on the ground.

tractor footprintThis rear tyre here always has a huge amount of tread on the ground, therefore giving the tractor lots of traction. The same exaggerated example can be used with excavators and bulldozers with big tracks. The length of their tracks are immense and is why they never get stuck, so clearly the length of your tyres footprint offroad means the more traction you have.

TYRE STRENGTH LONGEVITY

Another thing you need to consider when lowering your tyre pressures for 4WDing is protecting your tyres and ensuring their lifespan.

PSI comparisonWe put a GoPro camera inside this Goodyear Wrangler to see how the tyre reacts at different pressures when driving over a rock. At 40psi there is no indent seen, and at 20psi and 15psi you can clearly see the tyre morphs and moulds itself right over the obstacle.

At 40psi, your tyre does not have a lot of give when driving over rocks and logs. Out in the bush, your tyre needs to form over these obstacles, so it doesn’t break, slash, or pierce the tyre.

tyre mouldingYou can see here just how much more the tyre is able to mould itself around this tree stump at a lower pressure. This lower PSI means more traction, less pressure on your tyre at the point of impact, and less likelihood of the trye being damaged.

If you watch your tyre when you re-inflate them from low pressures, you can see as the trye pressure increases, the amount of tread touching the ground decreases.

BEACH 4WDING

40psi

For demonstration purposes we ran highway pressures of 40psi on the dry, soft sand of Shauno’s local beach to see what happens. Straight away you can feel the vehicle doing its best and working very hard to push you through and stay above the sand.

Pretty quickly Shauno’s big and heavy 200 Series LandCruiser bogs down into the sand while running 40psi.

20psi

We decide to take the pressures down to 20psi while bogged in the sand to see if we can drive straight out. This pressure is normally a good starting point for beach driving.

With no effort, the 4WD was easily able to drive out of the sand bogging by simply deflating the tyres from 40psi down to 20psi.

Another thing to note with the tyre pressures now down to 20psi, the vehicle is driving so much easier and working less hard. Deflating your tyres isn’t just to avoid getting your 4WD stuck, it is also about how much stress your vehicle is put through. Your engine, gearbox, diffs, drivetrain and almost everything else is under less stress because it is much easier for your 4WD to roll over the soft sand in comparison to higher tyre pressures.

dirty 30 sand beach

Ideal Beach Tyre Pressures

During this test with the weight of Shauno’s 200 and the conditions of the beach, we found 20psi to be perfect. This may not be the case all the time as every single beach is different and so is every 4WD. Softer sand or lighter vehicles can create different combinations, needing slight adjustments to your tyre pressures to find the ideal PSI.

The way to find out if you have set your tyres to the correct pressure for sand is to do Shauno’s “Little Stop Maneuver”. This is where you drive down the beach, you take your foot off the accelerator and your vehicle should come to a rolling stop rather than an abrupt halt. If your 4WD rolls a few metres before you stop, your tyre pressures are perfect. If the vehicle feels as if you’ve put your foot on the brake, then your tyre pressures are too high.

MUD, RUTS & ROCKS

When you find yourself in a situation offroad where you want to drive in mud or over big rocks and ruts – all the technical low-range 4WDing – you want to drop your tyre pressure down. One of the things that you would find if you don’t reduce your tyre pressures, it is going to be a hard and uncomfortable ride, not to mention you are not going to get the traction you need. The hard ride is also going to make it a lot more damaging on your vehicle, so take the time to deflate your tyres.

Shauno typically goes down to around 20psi when driving Sooty on tough 4WD tracks, and potentially lower at times depending on if it is very thick mud.

40psi

We tested an off cambered track with slippery clay and ruts, and Shauno tried to idle up at 40psi to see what would happen. Everything is so much harsher on the drivetrain, and every time he hit an obstacle he would bounce and slide around. Not only was the drive harder and more uncomfortable, Shauno could not idle up the track.

20psi

With essentially half the air out of the tyres, we reattempted to idle up this obstacle. With ease and comfort, Shauno was able to smoothly idle Sooty up the track with no issues.

HOW LOW IS TOO LOW?

Many people worry when letting their tyre pressures down with standard rims that they will roll a tyre off a rim. This is definitely a possibility when you let your tyres down too low, so the question is – how low is too low?

We strongly believe that you are not going to pop a tyre off the rim if you drive in a straight line without any erratic movement. So, if you are stuck on the beach and you really need to let your tyre pressure down, and you’re still stuck at 15psi, let them down further.

Shauno has let his PSI down to below 10 on standard rims when stuck in sand, and by driving in a straight line, he was able to get out with his tyres and rims intact.

But, if you are going to do some crazy, full on driving up rock steps – with turns and a fair bit of right foot – then driving on those sorts of pressure without bead lock rims run a real risk of having a tyre come off the rim. Don’t be too shy about rolling a tyre off the rim by letting out a bit of pressure, because if you drive normally, it shouldn’t happen.

CORRUGATIONS

40psi

First thing you notice driving over corrugations with 40psi, even in comfortable 4WDs like Shauno’s 200, the vehicle does shake and bounce around a heck of a lot – even at only 60km/h. You can hear and feel how rough this is on your 4WD when running highway tyre pressures.

20psi

With a quick deflation of the tyres down to 20psi, the difference is instant as it is much quieter and more comfortable in the cabin, and definitely more refined. As your tyres are the first part of your suspensions, the lower pressures dampen the feel of the corrugated road.

Not only is the shaking dampened for comforts sake, the chassis, driveline, and components of your 4WD like your tray have the impact and shakes softened too. When running highway pressure on dirt roads and corrugations for long stretches, your vehicle will literally shake itself to pieces.

Ideal Pressures for Corrugations

For Shauno, considering the size and weight of his 200, running tyre pressures around 26-28psi is the sweet spot. The vehicle handles and corners well while still reducing the shaking, especially when hitting rough corrugations.

ON ROAD TEST

Under Inflated Tyres

Lots of people have done it, gone out 4WDing and then snuck out into town or even driven home without putting your tyre pressures back up to highway PSI. The problem is that incorrect tyre pressures is the leading cause of bad tyre wear.

While you are driving with a low tyre pressure, your tyre expands and contacts hundreds of times per minute. This movement causes friction, and all that friction causes heat. This heats up the rubber and the steel belts within your tyre, slowly degrading your tyre over time.

  under inflation wearBreaking this down: the more deflated your tyre means the more give they have, allowing for more movement, which means more friction and heat generated, and the more heat results in faster wear and degrading of your tyres.

Over Inflated Tyres

It is also dangerous to have your tyres over inflated. The more pressure in your tyres results in less rubber in contact with the road, meaning the middle wears out too fast and you won’t have enough grip.

Correct Pressures

It may be annoying having to pump your tyres back up, but it is definitely the best thing to do. Stop for 5 minutes to hook up your air compressor, have a stretch, and thank yourself for giving your tyres a few extra months of life.

WHAT HAS THIS TEST TAUGHT US

If this test has taught us anything, it would be that altering your tyre pressures is going to make a huge difference while 4WDing – not just the performance of how far you can go without getting bogged or stuck, but also how it will protect your tyres as well as your 4WD.

The fundamentals remain the same, it doesn’t matter what terrain you are driving on, you really need to adjust your tyre pressures accordingly. You will find out for yourself the adjustments that suit your vehicle on whatever terrain it may be, that will make your 4WD more capable and that much more comfortable, getting yourself further off road.

For us, this is our number 1 modification for any 4WD because not only is it free, but it so easy – heck, even using a little stick from the side of the road can make your 4WD more capable in the matter of minutes!