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4X4 suspension modification laws; ‘Suspension Manual’ published

BySam PurcellDecember 14, 2016
4 MINUTE READ
4X4 suspension modification laws; ‘Suspension Manual’ published

Duncan Gay, the minister for Roads, Maritime and Freight, has just released the ‘Suspension Manual’ document, which is the new rules for 4X4 suspension modification laws in New South Wales.

Why do you need to know about it? If gives clear and concise guidelines on what’s legal, what’s not, and what needs engineering. We’re crossing our fingers (and toes) that this becomes the basis for a national code of suspension modification laws for all Australian 4WDers.

Navara NP300 TJM bullbar

Suspension lifts are a great way of improving your off-road capability, providing it’s done well.

This story follows on from our recent story about suspension law changes.

You can look at the manual here. Otherwise, read on for the juicy bits:

Minor Modifications

‘Minor modification’s are things that don’t require assessment or engineering before being deemed road legal. In other words, this is what you can do to your 4X4 before things get serious:

  • modifications to the suspension that does not increase or decrease the vehicle’s ride height by more than 50mm.
  • Changes in the diameter of the wheel and tyre combination of up to +/- 7% of the largest size specified by the vehicle manufacturer.
  • Modifications to the ride height up to 75mm that incorporate a maximum change in the suspension of 50mm, and/or an increase in the diameter of the wheel and tyre combination of up to 50mm.
  • Changes in the vehicle’s ride height by up to 50mm by replacing the rear coil springs with air springs fitted to un-modified, original mounting points when used with slow speed air controls in accordance with Appendix B.6.1a
  • Changes in the vehicle’s ride height by up to 50mm by replacing the rear shock absorber assemblies with air adjustment, fitted to un-modified, original mounting points, when used with slow speed air controls in accordance with Appendix B.6.1a.
  • Supplementary air springs that assist the original springs, and are fitted without other
    modifications, such as holes drilled in structural sections of a chassis.

This document of suspension modification laws effectively overrides VSB14, and gives 4WDers more scope for effective suspension modification.

Nissan Patrol suspension modifications

With a 50mm suspension and 50mm tyre increase, you’ll have a 75mm (3″) overall ride height increase.

ENGINEERING

If you’re dead-set on getting an engineer involved in your build, you’ll have to consult one if you:

Increases the vehicle’s ride height between 50mm and 125mm; or of up to 125mm that combined with an increase in the diameter of the wheel and tyre combination of up to 50mm increases the vehicle’s ride height between 75mm and 150mm.

These lawmakers aren’t much chop at writing effective sentences, are they? What they mean is: If you do a suspension lift of over 50mm, you’ll need an engineer. If you do more than a 50mm suspension lift and fit 50mm taller tyres (75mm total lift), you’ll have to get it engineered. Otherwise, you’re in the clear.

So effectively with these new rules, you have more room to play with overall ride height, provided that you use tyre diameter and suspension lift to achieve it. Body lifts are still off the table, as well as wholesale changes to suspension types, or modification of mounts or points.

The document goes to great lengths and pains to recommend people to thoroughly plan and research their modifications to their vehicle, particularly 4WDs destined for off-road tracks. For example, a 75mm lift through 50mm suspension and 25mm tyres will quickly evaporate under the weight of bullbars, winches, extra spares and other associated gear we all love on our 4WDs. So if you want to do an effective suspension lift that is a ‘true’ 75mm overall lift, you will need to look into stiffer and/or longer springs.

An extra note here: taller suspension does not instantly mean better off-road performance. Sure, your vehicle will be higher off the ground, but stiffer springs will reduce articulation and stability over rough terrain, and will put traction in a much shorter supply. Also, your centre of gravity gets worse, affecting your on-road and off-road performance negatively. If you’re keen on improving your off-road capability, static ride height is only one element you need to consider.

It gets a little bit tricky, however. Let’s imagine a big 4WD wagon like a LandCruiser or Patrol. You whack on a bull bar, winch, rear bar and twin tyre carriers. Let’s say, for argument’s sake that’s a total of 220-odd kilograms. You add this into your suspension mods, ensuring you have 75mm total lift with your extra weight. But then, for your daily commute, your remove one or two spare wheels, or you convert your steel winch line into lighter synthetic. You need to be aware that your suspension will effectively increase in height with these changes, and could potentially render it a ‘significant modification’, therefore legally requiring engineering. Like all good laws, this does become a bit of a grey area.

Toyota HiLux suspension modifications.

The trick for suspension modifications is accurately gauging what your vehicles and accessories weigh, and adding it into the equation.

TOLERANCES

I mentioned grey areas before, right? This document calls them ‘Tolerances’, and allows for changes in your height from changes in your tare mass, or slight variations in the modified components. The amount is 15mm, give or take. If you are in that situation of big changes in mass, whether it be full long-range tanks or whatever it might be, that gives you a realistic room to wiggle, which we think is brilliant.

HOW DO I MEASURE MY RIDE HEIGHT?

Good question, and it’s one that’s answered by this significant document. It recommends you measure ‘arch height’ which measures the vehicle’s height via the highest part of the wheel arch. Or, you can measure ‘running clearance’, which is “measuring the distance from the supporting ground to the vehicle’s lowest point excluding unsprung mass. In taking the measurements, the vehicle should be supported on a firm, nominally horizontal surface, with the tyres inflated to the nominated pressure and the vehicle in the unladen state. The arch height or running clearance as measured should be recorded and photographed for future verification.”

Our opinion in this whole thing is that it’s a great step forward for the 4WD modifier. The laws have actually been brought into something of a semblance of real-world usage, making the laws relevant and real. 4WDers now can 100% legally commit to suspension any wheel/tyre changes that don’t make a big different to their safety, braking or handling. Big suspension lifts, body lifts and significant increases in tyre diameter still need engineering, which is still a good idea: road safety is very important, and the door is open for those who want to chase massive increases in off-road capability … it’s just going to cost them a bit more of the folding stuff.

What do you think about these new suspension modification laws? Have your say in the comments section below.