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Staying legal can be difficult and a GVM increase may be needed.

As 4WDs become heavier and the list of ‘essential’ equipment increases, many 4WD owners find that their pride and joy is overweight. There is a way around this situation, but it mightn’t be cheap.


If you check out the true empty weight of a new 4WD you’ll get a shock: modern vehicles are much, much heavier than those of yesteryear. The reasons are simple enough: modern 4WDs are larger and they carry a lot more standard and optional equipment.

Typical new 4WD wagons have a payload rating around half a tonne to 750kg, but that ‘payload’ includes the weight of the people on board, fuel and aftermarket equipment that usually includes a fridge, second battery, roof rack, bar, winch and second spare wheel and tyre. Little wonder that most wagons are overloaded when filled up with food, water and camping and recovery gear.

These days, most wagon owners opt to tow a camper trailer or cross-over van for bush expeditions, because there’s just no way of fitting all their kit on board a solo vehicle.

However, coupling up to a trailer doesn’t necessarily solve the overloading problem and we’re sure you’ve all seen heavily loaded 4WDs towing heavy campers and vans.

Utes are a popular alternative to wagons and have greater payload capacity. Utes make great tow vehicles and are also ideal hosts for the increasing number of slide-on camper models in the marketplace.

It would seem that a nominal payload of one tonne should be more than enough to handle the weight of a slide-on, but we’ve pointed out some of the pitfalls in another story on this site – Ute payloads aren’t what they seem.

The starting point in GVM compliance is knowing the vehicle manufacturer’s overall GVM rating – it’s stamped on the compliance plate – and the individual front and rear axle loads. (Often the sum of the axle weights is greater than the approved GVM.)

If you’re towing you also need to know the maximum permissible trailer weight the vehicle can pull, plus the permissible ball weight. The towbar should be rated for at least these figures and both should be plated on the towbar.

Then you need to know the actual loaded weight of your rig: load your solo vehicle or vehicle plus trailer combination as you plan to use it; top up the fuel and water tanks; stock up the larger; fill the fridge; put the family on board with all their kit and head for the nearest weighbridge.

Be sure to have the whole rig weighed, as well as the individual weights on each axle. If you’re towing, do a separate weight measurement on the towball, using a scale. Scary isn’t it!

Then you need to assess the total load, to see where you can reduce weight, and do the weighing exercise once more.



Pre-registration GVM increase process



Heavy 4WDs are now common enough to make it worthwhile for some aftermarket suspension makers to produce Federal authority-approved, legal GVM increase kits for popular brand-new wagons and utes.

It’s important at the outset to know that some sections of the original new vehicle warranty will be rendered void by a GVM upgrade. Typical warranty rejections by 4WD makers apply to the powertrain, brakes and chassis.

The suspension maker becomes a Second Stage Manufacturer (SSM), certifying the kit of parts that have been tested and shown to equal, or better, the handling and braking performance of the original vehicle.

However, these fitments need to be done to pre-registered new vehicles and the approval ties the owner to the specified suspension components to preserve compliance.

This latter point is important, because you cannot change any of the specified components without negating the GVM upgrade. An example is where a wagon has been granted a pre-rego GVM upgrade, using heavier suspension components to carry a heavy camping and equipment load, and the owner later wants to lighten up the vehicle and tow a camper trailer or caravan.

Federally-approved GVM upgrades apply Australia-wide and pass to a second owner who may live in a different state or territory. Post-registration GVM upgrades may use identical components, but require individual state and territory engineering approval.

The GVM-increased suspension is often found to be too harsh-riding at this lighter weight and the owner is tempted to fit softer-riding components. If this is done the GVM upgrade no longer applies. In some state jurisdictions, an engineer’s certification is required to restore the original GVM.



The testing and validation regime is strict, and very expensive, which is why only the larger after-market suspension makers have invested in it.

We were invited to attend several Tough Dog Suspension GVM upgrade testing sessions, both in their western Sydney laboratory and on test facilities at Sydney’s Eastern Creek Motorsport Park.

In developing these kits the business begins with a finite element analysis of the axle components, to ensure the assembly is up to handling the proposed weight increase.



In some cases, Tough Dog testing has shown some possible failure areas that are rectified as part of the GVM upgrade kit. Some kits include replacement suspension parts and wheel studs, in addition to new springs and shock absorbers, but in others the standard componentry stands up OK.

The Toyota 300 Series is a case in point, where most of the standard kit – apart from a modified rear coil spring seat – handles a GVM upgrade to 4139kg. However, in developing the upgrade Tough Dog engineers came up with replacement upper control arms and an adjustable panhard rod that are available for buyers who want additional strength and suspension adjustability.



Dynamic testing involves brake performance to ADR35 standard at the increased weight, including a partial brake failure test and a handbrake-on-incline test.

All new 4WDs have electronic stability control (ESC), so the testing also validates that performance of the ESC isn’t adversely affected by the increased weight and the increased ride height of the Tough Dog GVM-upgrade kits.



Tough Dog dealers are trained in the fitment of GVM-upgrade kits and the company keeps a central record of every pre- and post-rego fitment, with dealer, owner and vehicle details.



Post-registration GVM increase process


Already-registered vehicles can be granted GVM increases, but the process usually involves consulting with an engineer who has been approved by a state or territory authority to advise on, assess and certify vehicle modifications.

After-market suspension makers’ GVM upgrade kits are available for post-original-registration fitments. These companies’ dealers can provide engineering approval contacts to customers.

The principal downsides of post-rego GVM upgrades are the need for engineering certification and the fact that the approval is state or territory base and not transferable to an interstate second buyer, who will have to go through the GVM-upgrade certification process.

At OTA we’ve gone through the GVM increase process, with our Project 75 series ute, as it applied in NSW and while the details may be different in other jurisdictions the principles are the same.

Our vehicle has a wheelbase extension and upgraded suspension and brakes, and was approved for 3.5 tonnes GVM. The process took quite some time, cost around 15 grand in engineering time and hardware, and involved chassis strength analysis and brake performance testing.

The cost is greatly reduced to around five grand if you don’t opt for a chassis stretch and wheelbase extension.



Front and rear axle weight issues


Even with a legitimate GVM increase approval you may still not be out of the woods. The ridiculously heavy ball weights of most Australian-market caravans and imported forward-fold camper trailers place high-load demands on the rear ends of towing vehicles, to the point where even an increased GVM sometimes can’t prevent the rear axle and suspension from being overloaded.

The loaded vehicle, with its van behind, may not exceed the combination’s GCM rating, but it’s possible that the rear axle of the towing vehicle can exceed its individual axle rating. If you’re split-weighed by the authorities you could be axle-weight illegal, even ‘though you’re GCM legal.

It’s a situation heavy truck operators are very familiar with, which is why some carriers – particularly loggers – have on-board weight scales fitted to their prime movers and skeletal log trailers. These strain-gauge or air-bellows-mounted devices show the loaded weight on each axle in real time on a dashboard display in front of the driver.

The most commonly-seen, 4WD-related rear axle towing overload are Toyota’s 200 and 300 Series, coupled to heavy caravans, with high ball weight loading. Almost every such standard-suspension combination is illegally heavy over the rear axle, even with weight distribution bars in action.

The 200 Series’ standard rear axle and suspension assembly is rated at only 1950kg and there are several upgrades available, including Tough Dog’s 2200kg upgrade. In the case of the 300 Series the Tough Dog rear axle weight goes up to 2239kg.

The heaviest-rated solution we’ve seen is JmacX’s fabricated replacement axle that has a load rating of up to 3000kg.

Front axles can also be unwittingly overloaded, by fitting accessories such as a steel ‘roo bar, winch and under bonnet battery. Most popular utes and wagons, fitted with a steel bar and side rails and a large winch, have overloaded front axles.



GVM increase guidelines


There is no margin allowed with GVM: if the vehicle is overweight it’s illegal and can be grounded by state or territory authorities or police. There are heavy fines for this offence and insurance companies have been known to reject claims if vehicles are found to be overweight.

If your vehicle weighs-in heavy you may be able to have it assessed by an engineer for a GVM upgrade, but don’t even think about it unless the brakes and axles are in top condition and there’s no rust or damage anywhere in the body or chassis.

As a rough guide, an increase of around 10 percent may be possible through suspension upgrades. An approved engineer will check the maker’s axle weights and any modifications made to the vehicle, before specifying upgraded springs and dampers.

With the engineer’s time and new hardware the cost could be more than four grand.

alan bradley ute gvm increase If a brake upgrade is required there’s more hardware cost and the braking system may need to pass a fade and performance test. More money.

If the needed GVM increase exceeeds 10 percent the engineer may suggest an axle swap, or a wheelbase increase with an additional rear axle and that’s a much more expensive exercise. As a rule, it’s best to consult a specialised vehicle modifier for such tasks.

In some cases a GVM increase is needed to handle the ball weight of a camper trailer or caravan. Key points an engineer will examine are the axle, brake and suspension capacities and the strength of the drawbar and chassis.

It’s important to note that every GVM upgrade is conditional on maintaining the approved configuration, specifically spring and shock absorber type and model number.

Any deviation from the approved components would need to be engineer-approved.



No automatic GCM increase


Most people assume that after a GVM increase the vehicle’s trailer towing rating remains the same, but that’s not the case since June 1, 2018.

Before that date some GVM modifiers plated the vehicle with an increase in its GCM (Gross Combination Mass, or the weight on all the vehicle and trailer tyres when loaded with people, fuel and freight, and coupled together).

This grey area of the law has been clarified and any GVM increase does not increase the original vehicle manufacturer’s GCM figure, which the legislation says cannot be increased.

For example, consider a ute with a standard GVM of three tonnes and a manufacturer’s GCM rating of 6.5 tonnes. Its manufacturer’s trailer towing capacity is 3.5 tonnes. If this ute gets a legal GVM upgrade to 3.3 tonnes, its GCM remains at 6.5 tonnes.  If the ute is loaded to its new 3.3 tonnes GVM it can legally pull a trailer weighing only 3.2 tonnes.

However, our research indicates that engineering work and approval may allow GCM increases in some instances. We know that NSW engineer, John Wilson, who did the approval on our OTA 75 Series’ GVM increase, has conducted tests for a GCM upgrade for the Toyota 200 Series.

He tested a 200 with a four-tonnes-ATM caravan, to measure its repeatable startability on a 23-degree incline and its gradeability at 80km/h on a one-percent highway grade.

Contact John Wilson if you wish to modify your 200 Series for up to four tonnes trailer capacity, along with GVM increase to 3.9 tonnes, for a total engineer-approved GCM of 7.9 tonnes.

John Wilson’s web address is vehicleengineering.com.au.



Another case study


A regular Victorian OTA website visitor went through a GVM upgrade exercise on his 2006 ex-Telstra cab/chassis, leaf-sprung Patrol, in 2013. The factory GVM was 3400kg.

After fitting it out for long-term remote area travel and, subsequently, going through a weight reduction exercise, he found the weight in full touring mode was still 3700kg, and he felt unable to shed that 300kg without significantly affecting the integrity of the fit-out.

The answer was a GVM upgrade using the 3900kg Lovells GVM-upgrade kit normally reserved for new, unregistered vehicles that have three-litre engines, not the 2006 4.2TDi. Consequently, the vehicle had to be engineer-approved and fortunately an engineer familiar with the Lovells GVM-upgrade kit was on hand to do the job. 

Brake proportioning was altered and static handbrake and dynamic wheel-brake tests had to be passed. Although the factory brakes passed the tests the front discs and pads were later upgraded.

The cost of engineering was $1200 above the cost of the kit, for a total layout of $5200.

OTA thinks this was the first retro-fit Lovells kit approval in Victoria, so there was no certainty that it would all go through; making it a nail-biting exercise until the blue plate was placed on the firewall.

Our thanks to Alan Bradley and Ian Lock, the AAAA, Tough Dog and engineers John Wilson and Mario Larocca in the production of this article.




























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