Tyre Pressure Basics | Why And When To Deflate Your Tyres

Article from: REDARC Electronics

Andrew and Peta Murray from Top Wire Traveller travel all over Australia in their truck camper. They travel over all types of terrain, from smooth freeways to the roughest desert tracks. Here they share what they’ve learnt from many years of off-road driving.

Tyre Pressure Basics – Why and when to deflate your tyres

Tyre pressures are a never-ending source of debate and opinion. Some people deflate their tyres to suit every different road surface and condition, while others refuse to adjust their tyre pressures… ever!

We’re somewhere in between. Generally we run just two sets of tyre pressures, one for on-road (tar) and another for off-road (not tar!).

And we air down further only if the situation calls for it.

So, what’s a good guide? And why do you even need to deflate your tyres? We’ll answer the second question first, then we’ll give you a tyre pressure guide for varying situations.

Why you should deflate your tyres off-road

Imagine a fully inflated balloon. You touch it with a toothpick, and it pops instantly. Now try popping a partially inflated balloon with a toothpick. It’s actually quite difficult!

The same basic principles apply to your 4WD tyres.

Say you’re punting down the Tanami Track, with your tyres inflated to road pressure. You drive over a sharp mulga stick. Chances are, it will spear straight through your tyre.

If you’d have let some air out of the tyres, they might have been pliable enough to flex over the mulga stick. Just like the partially inflated balloon and toothpick we talked about earlier.

Flat tyre or blowout averted!

And this is why you need to deflate your tyres off-road. Less pressure allows the tyres to flex more.

Not only this, you’ll get a better ride over rough surfaces like corrugations and rocks. In turn, you won’t be shaking your vehicle to pieces as much.

The other thing worth mentioning here is road speed.

We never travel over 80km/h on dirt roads. One reason is because you never know what ugly washouts or holes are around the corner.

The second reason is tyre damage. Imagine firing an arrow from a crossbow at your tyre. By the way, we don’t recommend this! The arrow will go straight through it. Now try throwing the arrow at the tyre. It’ll simply bounce off.

Now imagine firing a sharp stone at your tyre out of a gun, at 100 or even 120km/h. Chances are it’ll pierce the tyre. Will it pierce the tyre at 80km/h? Maybe, maybe not.

But at least there’s a better chance it won’t pierce the tyre at the lower speed.

If you then combine both lower tyre pressures and lower speeds, you significantly reduce the likelihood of getting a flat tyre or blowout.

An invaluable resource

Since we’re talking tyre pressures, there’s a secret resource available that most people don’t know about.

Contact the manufacturer of your tyre and ask them what pressures they recommend. They’re the experts about your brand of tyre. Most are more than happy for you to contact them… after all, blown tyres are bad for business!

We did this with the Toyo tyres on our truck. They were really helpful.

They should ask you two questions:

  1. What size and model tyre do you have? The size is written on the tyre and will be something like 285/70R/17. The model will likely be A/T (all-terrain) or M/T (mud terrain). Or it could be a name imprinted on the tyre. For example, our truck tyres are Toyo Hyparadial.
  2. What’s the weight on your front tyres and rear tyres? This is easy to find out. Take your vehicle to your nearest weigh bridge and ask them to weigh it. Easy! Go here for a full list of public weigh bridges in Australia.

How do you get in touch with your tyre manufacturer? The easiest way is to find them on Facebook, then send a Messenger message. The other way is through their Contact Us page on their website.

Ask your tyre manufacturer for a set of pressures for on road and off-road driving.

Now, let’s look at some broad guidelines you can follow for your 4WD.

A guide to correct tyre pressures

These are a broad guide only and depend somewhat on how much weight your vehicle’s carrying, tyre size and type. As we said earlier, contact your tyre manufacturer for the best information.

Having said that, here’s a few guidelines you can follow. These are based on a 4WD loaded for a trip away.

The 5psi rule

Tyre pressures are always quoted as “cold” pressures. The tyre heats up as you drive, and pressure increases as the air inside the tyre heats up.

An excellent guide to whether you’re running the right pressures is the “5psi rule”. Note this really only applies to on-road or smooth gravel roads.

Check your tyres when they’re cold and again when they’re hot (after driving on them for ½ hour or so). If the difference between cold and hot tyre pressures is around 5psi, then you’re running the right pressures.

If it’s less than 5psi, the pressures are probably too high. If more than 5psi then your pressures are too low. Add or remove 5psi at a time and check again. Repeat until the difference between hot and cold pressures is around 5psi.

Now, here’s a few starting points for some of the conditions you might encounter in your 4WD.

Starting points for different conditions

Most of the time, you’ll only need to use the “On Road” and “Off Road (High Range)” pressures listed here. Keep the others in mind for when you get stuck in a nasty situation.


On Road:

  • Tar or smooth gravel.
  • 38 – 42psi.

Off Road (High Range):

  • Rough, stony or corrugated dirt.
  • Driving in High Range.
  • 28 – 30psi.

Off Road (Low Range):

  • Mountainous fire trails or really rough tracks.
  • Driving in Low Range.
  • 20 – 28psi.

Sand:

  • Depends on how soft the sand is.
  • Start at around 25psi and reduce by 5psi at a time until your vehicle stops digging in.
  • You can go down as far as 15psi or even 10psi if you’re badly stuck. But be really careful. At these low pressures you can easily roll the tyre off the rim. Re-inflate as soon as you can.

Mud:

  • Depends on how thick the mud is.
  • If it’s thin and watery, leave your tyres at 28 – 30psi.
  • If it’s really thick and sticky, you might have to go as low as 18 – 20psi.

In summary

Knowing what pressures to run your tyres on and off-road should be simple… one pressure on-road and another for off-road. Unfortunately there’s plenty of misinformation floating about, both online and in the real world.

Keep it simple. Slow down on gravel and deflate your tyres once off the tar. And enjoy your off-road adventure!

You can follow Andrew and Peta’s outback travel adventures via their website and on FacebookTwitterPinterest and YouTube.

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Comments 7

  1. Something not mentioned in the article and is actually quite common is a tyre with high pressure on a dirt road with occasional stones can fracture the bond between tread and the steel belts, causing tread separation. Found out the hard way on rail access roads over many years.

    1. yes same with low pressure on Gibb last year ,had to lend spares to get travelers out of trouble due to slicing of bulging walls,Just done the Plenty expert was told 60psi by locals [had BT50 dual cab with extended tray & tow bar ,spares on rear & all weight packed to the back]towing MDC 17 dual axle long tow bar]did 2 tyres in 100k of dirt,also busted his sissor jack trying to lift ute & caravan without unhitching or at least using jockey wheel to assist.Only had 60k to go to next station ,but you saw the spares he had put on & none in reserve,hope he made it without inconveiniencing any other poor buggers,His wife the expert could not be told to reduce pressures or turn around & try to get new tyres[I had never seen the brand before] & a jack,I thought the old fella was going to have a heart attack as he was grossly over weight & unfit. If not for my son travelling with us in convoy he may have had a long stay on the side of the road.

  2. I’ve heard of the 5psi rule before, (it was 4psi when I heard it but close enough). I run 7.50R16 on my (lightly loaded) Troopy. I can get 10psi of difference between hot and cold temps. (I run aTPMS system). So theoretically I should be increasing the pressures. I’m already running 65 in the back and 60 in the front.

  3. We came up the Canning from South to North in June towing a Mark II T-Van. Ran 15psi front, 18psi rear on the Amarok and 15psi on the van. No punctures and didn’t get stuck on any of the dunes despite the prophets of doom going South telling us we would – including the two owners of the 79 Series who were running 38psi.

    Got passed by an Okka when we were camped at Slate Range and bumped into him at Parry Creek a few weeks later – he said he owed us an apology as he thought we were chopping the track up but realized once he was ahead of us that we were doing the opposite due to the low pressures we were running.

    Also went up to the tip of Francoise Perrone National Park with the van in tow – very impressed that Parks WA provides a tyre air down/air up facility at the start of the 40km very sandy track, as does the council at Coral Bay!

    Did the Savannah Way and the Gibb last year and the Gibb again this year, along with many tracks worse than the Gibb (public section of the Tom Price Railway Road for one) running 24psi, 28psi and 24psi on the van.

    Have done two tyres in the last 40 years – both in the early days before I adjusted tyre pressures to suit the conditions.

    Lucky I guess but we’ve done 12,000k on the dirt so far this trip and all good – perhaps the Old Eyre Highway will change it for us as we head East the day after tomorrow!

    And as for those who refuse to lower their tyre pressures in sand – please don’t ask me for a tug because I will politely decline.

    I have run as low as 10psi (getting onto the beach at 48 Mile with the van the Coorong) and not had to get the Maxtrax out or had a tyre come off a rim…

  4. Here is one for the experts to chew over. I have a HDJ100. I have run 40 psi for nearly 300 000kms in the vehicle on bitumen at all speeds and all loads up to GVM, and I have gotten excellent even wear out of the BFG’s LT tyres over that time. I recently purchased a high quality TPMS which displays very accurate pressures at all times (Loran) to travel out to the BRB. The pressures up to GVM increase about 4-5 psi up to 110 km/hr, on bitumen so I figure 40 is a good cold pressure for the vehicle. We recently purchased a 18′ Bushtracker and loaded up weighed 3300 kg. About 280kg of that was on the tower. NOW while towing the van with the Landcruiser at 80-90 kph at GVM including the tow bar weight I started with 45 in the rear and 42 in the front. The fronts went to about 48 once warm, however the rear went to 55 (so under inflated right?). The next day I adjusted the rears to 50 and left the front the same. Same conditions and the rears went to 60 once warm, fronts went to about 48. (so rear still under inflated right?) I checked the sidewall and the max. pressure is 70psi, for these tyres. Expecting perhaps another 10 psi increase, I again inflated the rears but only to 58 cold. Rear pressures increased to about 68 psi. and I noticed the sidewall bulge was less than the front when warm, so I decreased the rear pressures to 48 psi cold and just accepted the 10 psi increase as the sidewall bulge once warm looked about the same as the fronts????? I asked numerous people why the pressure increase was so dramatic and then looked at lots of shrugging shoulders?? I believe it is just the load on the rear tyres pushing from the drive train pushing through those tyre carcasses pulling approx 6.5 tonne load along? I reduced the rear pressures to 45 for the leg across the gravel corrugated road from Windorah to Birdsville and they still increased to about 55 even at about 60 – 80 kph.

  5. Weight definitely needs to be taken into consideration with tyre pressures. More weight will put more rubber in contact with the ground when dropping pressure. Instead of just aiming for a pressure it can be good practise to check ur footprint and adjust accordingly to balance ur ride.

  6. Like yourself, I contacted the manufacturer (Toyo) and obtained the correct tyre pressures to run based on the weight of the vehicle and the tyre used. I have a good handle on the weight of the vehicle at any time, and any change is generally on the rear axle.

    With this information in hand I run pressures according to the calculated pressure.

    This article is a bit of fresh air compared to the usual tyre pressure discussion, which usually has people quoting a “one pressure fits all, without any reference to the weight carried by the tyre.

    The difference I apply for on/off-road use as suggested by the technical area at Toyo is 8psi.

    The only time I deviate from this is when I am in sand, or if I loose traction.

    I have monitored tyre use over many thousand’s of KLMs (160,000 in current vehicle) and I can say I have lost more tyres due to under-inflation, mostly induced by heat from too much flex, or staking in the sidewalls – a great incentive to run the “correct pressures” based on the manufacturer’s guidelines, especially since I’m the bloke that pays for the tyres…

    Great article!

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