BLOW HARD

THE INS AND OUTS OF THE UPS AND DOWNS OF TYRES – A GUIDE TO TYRE-INFLATION METHODS.

WORDS AND PHOTOS DAN EVERETT

SINGLE PISTON THE tried and tested option is the venerable single piston compressor. They’ve been the go-to option for airing up tyres since there were tyres to air up, and they still pack a hell of a punch when it comes to bang for buck. We roped in a Flomax item from Ironman 4x4 and it’s the perfect example of what you want in a single piston unit. Despite being super affordable it’s still a quality item with a warranty and bunch of safety devices included. Its diminutive size also means you’re able to throw them in and out of different 4x4s without needing a fridge trolley to swap them over. They’re dirt cheap, too, at a hair over $150. That small size isn’t without its drawbacks though. At 72L/pm flowrates it’ll take twice as long to air up tyres as the more expensive options, and, without plumbing in an elaborate air-tank setup, running air tools is a distant thought; although, the included attachments means it’ll tick the box for air mattresses and inflatable toys.

TYRES are the foundation of everything we do as four-wheel drivers – whether they’re pumped up to road pressures for long stretches of black top, dropped down to smooth-out corrugations on outback tracks, or running single-digit pressures for huge footprints and ample grip in rocks and sandy terrain. The problem is, while airing down to the appropriate pressures is as easy as unscrewing the valve, airing back up is a completely different ball game.

For years it’s been a simple, albeit slow, affair: a 12V compressor rattling around in a canvas bag in the back of your 4x4, a couple of gator clamps onto your battery, and, after a 20min wait and a seemingly endless bone-rattling drone, you might be good to go.

These days we’re spoilt for choice. There’s everything from your traditional single piston offerings, right up to complete onboard air systems and everything in-between. Each offering has its own unique set of pros and (occasional) cons thrown in for good mix. From lightweight portable offerings to powerhouses that’ll run a workshop full of air tools, the options are almost endless; in fact, endless is literally one of the options.

To help get you on the straight and narrow of compressed air, we’re shining the spotlights at some of the most versatile air systems money can buy.

TWIN PISTON STEPPING up into a twin piston compressor completely changes the ball game, in more ways than one. They typically step up a size compared to single piston compressors, allowing them to pump out two to three times the litres per minute of their smaller siblings. It means pump-up times can be halved, or you can pump up multiple 4x4s without needing to set-up camp for the day. The increased flow rate also means you’re stepping into air-tool territory. While air tools are seen as somewhat extreme for general touring duties, they can be used for anything from changing a spare tyre to winding down the legs of a camper trailer. Of course, it’s not all sunshine and roses. The extra work translates into extra heat and extra current draw, and the compressor itself can get red-hot. Some items are protected in hard cases, like this set-up, but others you’ll need to stack carefully if you’re throwing it into the back of your four-wheel drive. The ARB unit draws a huge 68.6amp through twin fuses, so you’ll need the engine running while you pump up. The extra size and weight increase is something to consider as well, especially if you’re in a SWB 4x4 or regularly packed to the hilt.

INDUSTRIAL UNITS IF YOU’RE the kind of off-roader who beats their chest and quotes Tim Taylor un-ironically, you might be enticed to roll out the golden credit card and get swiping. Industrial air systems, like the Oasis, may not be the most practical, but it’s also the only compressor we’ve found that’s exciting to look at. Sure, the cons are numerous – they cost more than a boat-full of Shanghai’s finest opium, and at 30kg, portability falls somewhere between outhouse and marble statue – but flick that switch and it all becomes worth it. Essentially an engine-driven compressor with a beefed-up winch motor, the result is a massive 400L/pm flow rate and 100 per cent duty cycle. It’s enough to inflate a 33-inch muddie in around a minute flat, or run a ½-inch rattle gun continuously without a tank. Alright, it might be overkill for your typical tourer, but for remote travellers or service trucks where performance and reliability are key the pros are worth the cons.

WHAT IT ALL MEANS 01 FLOW RATE Maximum pressure is the absolute highest pressure the compressor can pump into a tyre, typically they’re all in the triple-digit figures, so are almost irrelevant for 4x4 use. Flow rate is far more important and tells us how much air the compressor can pump. A compressor than can flow 200L/pm (litres per minute) will pump up a tyre twice as fast as one at 100L/pm. This can also be measured in Cubic Feet per Minute, or CFM. 02 DUTY CYCLE Duty Cycle is used to describe two things: how long the compressor can run, and how long it needs to rest. Different companies use different methods, but you can roughly compare them. Percentage means how much cool-down time it needs in an hour of operation. So 50 per cent duty cycle is 30 minutes on, 30 minutes off. Others are measured in time – where the manufacturer states 40 minutes, it’s implied it’ll need to rest for 20 minutes. 03 MAX CURRENT DRAW While average current draw lets you know how much power something will chew, maximum current draw is far more useful for knowing how strong your electrical system needs to be to deal with the stresses. It factors in the peaks in consumption you’ll find pushing against higher pressures, dealing with heat, or the large start-up loads. The higher the max current draw, the more load it’ll put on your four-wheel drive’s electrical system.

ENGINE-DRIVEN OFTEN known as an endless-air set-up, engine-driven compressors aren’t new but are few and far between in the 4x4 world. Much like a typical compressor, they’re a piston inside a cylinder; although, instead of a 12V motor the size of a coke can turning it, you’ve got a 200hp turbo-diesel donk. Mounted to the engine, then driven by a belt, the result is an endless supply of compressed air. As long as the engine is turning, the compressor can be too. Home-brew options aren’t unusual and typically use a modified AC compressor. It’s a slightly janky method that’ll require external oiling (the AC fluid usually does this job) and then an oil/air separator to not pump the tyres with oil. Aftermarket options with mounting kits offer simpler installation and safer oiling methods. You need the engine running; although, at 200+L/pm, any 12V compressor that could come close would need the engine, too. Factor in a few internal air-lines and you’ll have an onboard air system that’ll do just about anything you need it to.

DIVE TANKS SO everyone knows you need the pressure of compressed air to pump up your tyres, but no-one said you had to compress it yourself. A popular option in the USA, compressed air tanks are known for their rugged simplicity: there’s very little to go wrong, no load on your engine or electrical system, no need for elaborate hose systems and, they’re easily interchangeable between vehicles. They’re also capable of pushing out a simply insane 900L/pm thanks to their huge internal pressure. You’d need more than a dozen single pistons in a row to come close. That means there’s plenty of grunt for airing up tyres, powering small air tools or firing oranges at noisy campsites (with a PVC pipe). So why aren’t we all running them? Well, they’re expensive and, when you consider they have a limited supply of air in them, there are ongoing costs of around $30 a pop to get them refilled. You’ll typically get a solid half-dozen trips out of them before you need to start watching the pressure gauge with baited breath, though.