Tips on knowing your vehicle and trailer limits compared to your actual weights.

Not only is overloading your vehicle illegal but it’s also unsafe. When you carry more weight than the vehicle is equipped to handle, it forces the engine, suspension, axles and brakes to work harder than designed. This compromises the longevity of the vehicle and ultimately your safety on the road.

Use the below post to navigate through the technical jargon, find tips on checking your weight and use Ironman 4x4 products to ensure a smooth ride.

To skip to a specific section, click the below links:

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Sometimes it's best explained in a video.

Watch Robert Pepper, Automotive Journalist, explain what a GVM upgrade is and why you need them?


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The Technical Jargon Explained

There’s a lot of technical jargon thrown around when talking about vehicle and towing weights. We get that it can be confusing and sometimes seem all too hard, so we’ve tried to simplify it for you below.

Tare Weight

The tare weight is the total weight of your vehicle when it has left the manufacturer. This generally doesn’t include any after sales accessories you have chosen to add to your vehicle. If you have additions added to your vehicle at the time of purchase it is good to check what is and isn’t included in your tare weight.

Vehicle Payload

The payload is the allowable amount of weight you can put in your vehicle. Sometimes this is provided by the manufacturer, but it is simple to work out by subtracting the kerb weight from the gross vehicle mass.

Hot tip: always keep in mind that your payload needs to include fuel, larger tyres and any passengers onboard at that time.

Axle Limits

The axles, suspension and shocks in your vehicle are designed to comfortably carry a specific amount and percentage of weight across your vehicle. The vehicle manufacturer sets a maximum weight that each axle can carry based on the OEM specification suspension. This can be upgraded with a GVM upgrade.

Gross Vehicle Mass (GVM) 

The gross vehicle mass, commonly known as the GVM, is the maximum amount of weight you can carry in your vehicle. This includes any passengers, fuel, vehicle accessories and luggage. If you are towing, this weight also includes your trailer ball weight. It is set by the vehicle manufacturer but like the axle limits can be upgraded with a GVM upgrade.

Vehicle Tow Capacity

Any tow vehicle has a maximum towing capacity set by the vehicle manufacturer. This includes the maximum tow weight and the trailer ball weight permittable.

Tow bar Tow Capacity

 Each tow bar has its own maximum tow capacity. Sometimes this can be different to the maximum vehicle tow capacity. 

If the tow bar is rated higher than the vehicle, the maximum tow capacity of the vehicle is the Vehicle Tow Capacity.

If the tow bar is rated lower than the vehicle, the maximum tow capacity is the Tow Bar Tow Capacity.

Hot tip: All Ironman 4x4 Rear Tow Bars are rated to the maximum set by the vehicle manufacturer.

Trailer Ball Weight

The trailer ball weight is the weight under the coupling of your trailer, creating a downward force on the tow bar. The vehicle, tow bar and trailer can have maximum trailer ball weight ratings. The lowest rating of the three is the maximum Trailer Ball Weight for your set up.

Trailer Tare Weight 

The trailer tare weight is the weight of the trailer when it has left the manufacturer. Note that in terms of camper trailers and caravans, if you have had additional accessories added, these may not be included in the tare weight and may contribute to your Trailer Payload. Check with your dealer at the time of purchase.

Trailer Payload

The payload is the allowable amount of weight you can put in your trailer. Sometimes this is provided by the manufacturer, but it is simple to work out by subtracting the tare weight from the gross trailer mass.

Hot tip: Remember your payload will include any accessories, luggage, fuel, water and load you add to the trailer.

Gross Trailer Mass (GTM)

The Gross Trailer Mass is the maximum trailer weight imposed on the trailer’s axle and chassis when coupled to the tow vehicle. This weight does not include the trailer ball mass.

Aggregate Trailer Mass (ATM)

The Aggregate Trailer Mass is the maximum trailer weight, when the trailer is not coupled to the tow vehicle. This means it combines the GTM and Trailer Ball Weight to provide the total trailer weight.

Gross Combined Mass (GCM)

 The Gross Combined Mass is the maximum allowable weight of the tow vehicle, trailer and load. Often it is assumed that the GVM plus the Vehicle Tow Capacity makes the GCM, however this is not always the case. In many cases, the vehicle manufacturer has set their own GCM that the vehicle can move. Check your vehicle owner’s manual to find the right figure for your vehicle.


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Checking Weights

Weighing your vehicle doesn’t have to be hard. There are many public weighbridges in Australia that allow you to weigh your vehicle and trailer for a small fee. To find an Australian Government weighbridge, click here.

Click the button below to download and use our handy sheets to compare your weights.


Finding your manufacturer set maximums

For your vehicle maximum weights, including your tare weight, axle weights, GVM and GCM, check the owner’s manual supplied with your vehicle. If you cannot locate the weight information, contact the vehicle manufacturer. 

To find your trailer’s maximum weights, you will need to locate the compliance plate of your vehicle. This is commonly found in the front boot of a camper trailer and caravan or on the chassis of a trailer.

Measuring your vehicle weights 

When you arrive at the local weighbridge, measuring your vehicle axle weights and GVM is easy. 

If it is a single deck weighbridge, roll the front axle onto the weighbridge and record the weight, then roll the vehicle forward until only the rear axle is on the deck and record the weight. Simply add the two weights to find your GVM. 

If it is a multi-deck weighbridge, as long as the axles are on each deck, it will record a separate weight for each axle and provide an overall GVM. 

Hot tip: if you are towing, your Trailer Ball Weight needs to be included in your GVM. If you are weighing the vehicle without the trailer attached, remember to add this weight afterwards as it contributes to your total GVM whilst on the road.

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Weighing your trailer, camper trailer or caravan

To obtain the GTM for your trailer, tow your trailer onto the weigh bridge, making sure all axles are on the deck. Ensure the tow vehicle is not touching the decks and record the total trailer weight. 

The trailer ball weight can be measured using a device like a tow ball weight scale or via a mathematical equation:

GVM (with trailer connected) – GVM (without the trailer connected) = Trailer Ball Weight

Tbm Weight

Some methods are more accurate than others and it all comes down to the way you have taken the weight, however, to find your ATM, you will need to measure your trailer ball weight. 

The ATM of your trailer is the total weight of the trailer uncoupled from the vehicle. To find this weight, add the GTM to the trailer ball weight.

Caravan Safety Check Days

If you live in Queensland or Victoria, you can get your vehicle and caravan checked and assessed for free, outside of COVID-19 restrictions. The caravan industries in each state have set up Caravan Safety Day’s to check over the gas, electricity, lengths and weights of your set up. Although events are currently postponed, you can still register for updates on the links below.

For the QLD Safety Checks through Caravanning Queensland, click here.

For VIC Safety Checks through Caravan Industry Victoria, click here.


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Suspension and GVM Upgrades

Although you can move load and weight forward, backwards or even removing the load, let’s face it, you want to carry what you want to carry comfortably and safely without a hassle.

A suspension upgrade is a great way to assist your vehicle to carry your load. Specialised to suit your vehicle and what you want to carry, the suspension kit can be set to carry a more permanent load or a temporary load.

But if you are overweight, a GVM upgrade could be your answer. A GVM upgrade can provide you the additional payload you need to cover what you want to do with your vehicle.

But why?

Every time you add load to the vehicle, whether temporary or permanent, the responsiveness of the Original Equipment (OE) suspension changes. The OE manufacturer designs their suspension kits for comfort above all else and the addition of load can compromise ongoing performance.

Upgrading your suspension to suit what you are doing with your vehicle can improve your ride and safety on the road moreover where weight is concerned it can assist to make you legal again.

Finding a kit to suit you

Suspension and GVM upgrades are designed to be suited to your specific circumstances. This ensures a solution that not only meets your needs but continues to produce outstanding results in the future.

We have range of solutions to fit your 4x4 in the below link. But if you are looking for more specialised advice, speak to the Ironman 4x4 team or your local GVM expert.

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Posted on 25/04/2020