Equipment Tests > Under the Pump

Issue: February 2007

Words and photos by Robert Pepper

4WD Equipment - Central Tyre Inflation (CTI)
* Armies swear by it
* Around since the '40s
* A 4WDer's dream

Imagine never having to manually inflate and deflate your 4WD's tyre again - welcome to the world of Central Tyre Inflation.

Tyre pressures are a lot like gear ratios. Which gear you select depends on what the vehicle is doing, and that varies from moment to moment. The optimum tyre pressure changes almost as frequently too. At high speeds, heavily loaded, you want high pressures. As soon the road turns to dirt you'll want to drop, and further again for low range work. Then maybe there's an extra-steep hill where you'd want another few psi out, then quickly back in, or a short bitumen transit. Perhaps you're about to hook up a heavy trailer. Or maybe it's silly o'clock in the morning after an extended daytrip and you just want to get home and not stop to air up in the cold rain.

The problem is that tyre pressures aren't easy or quick to change, so we tend to compromise and only change them occasionally. We bounce around in the rough for short distances, or wear out tyres on the bitumen when they're set low because it's too much trouble to air up or down for a short drive in different conditions.

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Now that excuse is out the window with CTI (Central Tyre Inflation), the term used to refer to systems that allow the driver to control tyre pressures from the cab, without stopping. CTI has been around since the 1940s and is widely used by the military and trucking companies that drive on a mix of soft and hard roads. It's also available as an option on large vehicles like Unimogs.

CTI, hasn't really been accessible to 4WDers until now, with kits available from AIR CTI. The setup is pretty simple; you need an air compressor, hoses to each wheel, a tyre pressure gauge where the driver can see it and a control box to inflate or deflate. The only tricky part is getting the air to the tyre. Exactly how that's done depends on the vehicle, but for many applications the wheel is removed, and a base plate added behind with an extension that pokes through the centre of the rim (the rotator). Then it's just a case of joining the rotator to the air hose from the compressor, and to the existing tyre valve. No modifications to the rim are required, and any competent home mechanic could install it. The system also works at full flex and maximum lock, and can maintain air pressure with a smallish puncture.

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