Getting the Pressure Right

With only a few exceptions, most new 4WDs are fitted with tyres designed for every day driving with little consideration for extensive use offroad, a weighed down vehicle or those that tow heavy rigs. Regardless of whether you take advantage of fitting better tyres, one thing that’s important is the regular management of their pressures.

Quality 4WD tyres are designed for a variety of demanding Australian roads which can dish out some harsh punishment. These may include touring where they may contend with long hours on searing hot highways, wet roads, rough corrugations, loose surfaces, rocks and mud etc. 

Regardless of the conditions I point my 4WD towards, it’s always my goal to maximise traction as well as minimise the chance of damage to tyres and the environment. Adjusting tyre pressures in adverse conditions has multiple rewards compared to driving at normal road pressures, such as lengthening the tyre’s footprint thus increasing traction, reducing the chance of tyre damage as they mould over sharper obstacles, softening the ride over rough tracks and minimising damage to tracks. Remember to adjust the speed as you adjust tyre pressures.

All vehicles have a recommended tyre pressure stated on the tyre placard normally located inside the driver’s door or pillar. Of course, these figures are recommenced for stock tyres for everyday road use. It’s worth noting these placards may have options dependant on the number of passengers or amount of loaded cargo, hence why even a stock 4WD requires tyre pressure vigilance day to day. These placard numbers are my suggested base line but adjusting tyre pressures for differing roads does comes down to trial and error. 

Just a couple of psi can determine if the 4WD struggles negotiating the path ahead or sails through with ease. So don’t be afraid to experiment with pressures to find what works best for your circumstances.

WHAT YOU NEED

When it comes to tyre pressures, I adjust for the different terrain, so allow me to suggest a few additions for your kit to ensure you get the most out of your tyres. After all, you want them to perform. 

The first essential item I carry is a good, clear tyre pressure gauge. 

I prefer the analogue style, using psi standard but that’s a personal thing. These can be found for around $15–20, or a bit more, and I have two on board as they’re quite fragile.

Next, of course is a means to adjust the tyres to the required pressures. Nowadays there are devices that not only assist in deflating the tyres but others that also assist in inflating them back to road pressures in a timely and, some would say, easier manner.

TO DEFLATE ONLY

In the old days (though it can still be relevant today), one used a stick lying around to push in the tyre valve until each tyre reached the required pressure, (others kept a nail in the glove box for such duties as it tended not to break). 

I carry an inexpensive valve changing tool with spare valves that does the job too. Whilst these work and cost next to nothing, they’re tedious and slow with continual checking of pressures with a separate tyre gauge. 

Next to consider are automatic tyre deflators like those manufactured by Staun being an old stalwart. They’re made of brass and I’ve seen them sell for well under $80. They come as a set of four pieces with a 6–30psi range which should do for most 4WDers. I believe they have versions to accommodate other differing pressure ranges too. Staun are also Australian-made, a rarity for 4WD accessories. 

Staun deflators screw onto each tyre valve and expel air to a predefined setting, then automatically stop. They are simple and work well as you can quickly deflate four tyres at a time whilst you make a cup of tea. As mentioned, they’re set to a specific pressure, however you can change the pre-set settings by making adjustments.

A similar concept to Staun are the American made Trailhead Tyre Deflators, which have been around for over 25 years and supplied via TJM outlets and online. I’ve seen them sell for under $75. What differentiates these from Staun is the aluminium body and internal adjuster rather than an external locking ring, which makes it nigh impossible to accidentally change the setting if they get knocked around. 

They come with an Allen key adjuster and a bonus pencil-style pressure gauge. The package includes a gauge chart for recommending pressures for different tyre sizes and vehicle weight, which I found fascinating, though it was set on Imperial standards.

The Trailheads take on a similar approach to Staun but with an easier method to adjust their pre-set settings. The Trailheads are set at 12psi default and, to choose a different pre-set pressure, simply use the supplied Allen key. Turning the spring-loaded valve a full turn results in a 1.5psi change — clockwise to increase, anti-clockwise to decrease the pressure setting. They were quite accurate.

Neither Staun or Trailheads are the best solution if you require varying pressures for ongoing varying conditions, though it’s still doable. Excellent, if for instance you regularly hit the sand and you pre-set them to pressures like 18psi. They weigh little and take up little space with their ‘leather’ style cases plus they need little effort to use. 

Next, there are tyre deflators with the convenience of built-in pressure gauges, though needing a few more steps to function. They’re popular, easily sourced for around $40–80, and are quick to deflate one tyre at a time. It works by temporarily disengaging the tyre’s valve, allowing a large volume of air to escape when you pull back on the slide. Once again, like the stick method, they require you to continually check the pressure by sliding the casing and repeating till you reach your required pressures. 

I still have an analogue-style ARB E-Z tyre deflator and had been using it successfully for many years. I did however notice the gauge has never been as accurate, showing two psi above true psi. Recently I managed to source a TJM version to see if there were any discernible differences in performance or function. Not really, though the TJM has a longer hose, an easier to read digital gauge plus bonus valve removal tool and spare valves.

The beauty of units like ARB and TJM deflators is the ability to make easy settings without referring to a separate gauge if conditions change or if you prefer different pressures front to back or your trailer. However, every couple of months, the ARB (and I suspect TJM’s will) occasionally required a squirt of machine oil which smoothed out its operation, but this resulted in greasy stains on exposed hands. They both come with a tough satchel for easy storage.

THE TEST RESULTS

I set a speed test to see how long they’d take to deflate four tyres from 36psi to 16psi. The valve changing tool took 2.55m per tyre so 11.6m for four tyres, including checking with a gauge several times. ARB took 2.06m per tyre but nearly 10 min for all four, including moving from one to the next. The TJM deflator was actually a little slower by about 20 seconds overall, however the digital read was temperamental when it came to consistency over four tyres. The Staun took 3.22m to do all four (not bad) while the Trailheads took just under four minutes. 

All devices came within an acceptable one to two psi range from true.

Disclaimer: The test undertaken was not a scientific one, so results could alter dependant on tyre sizes, speed of operator and environmental influences!

THE FINAL PIECE IN MANAGING TYRE PRESSURES

I usually go straight to 16psi for most of my offroading, so the Staun or Trailheads are my go-to deflator as they’re easy and quick.

Even though you can deflate any tyre with not much more than a twig, you’ll still need a quality air compressor to pump them back up. Try to avoid cheap compressors, as they run out of puff and will struggle to reinflate your mate’s tyres too. 

Normally I’d automatically suggest sticking with big brand names as they’re normally more reliable in pumping up multiple tyres, but I have used some not so famous units that perform admirably, so best ask around to see what others have to say.

For convenience, an air compressor can be hard wired to your 4WD (like I have) making it easy and ready when you are, though most are optioned with a bag for portability. 

Finally, ignoring having the right pressures can result in poor ride, traction, and tyre wear or even tyre failure, especially when travelling at speed or on tricky terrain. It’s important to get the tyres back to normal pressures once you’re on a hard surface.