Why get your Vehicle and/or Combination Weighed…

15 May

The Critical Importance of Weighing Your Car, Caravan, Trailer, Boat, Motorhome, or 4WD

Ok, let’s take it back to basics… and that is, why get your setup weighed?

Whether you're towing a caravan across the country, launching a boat for a weekend trip, or loading up your 4WD for an off-grid adventure, understanding your vehicle's weight—and how it’s distributed—is essential. It’s not just about compliance with road regulations; it’s about safety, vehicle performance, and protecting your investment.

Overloaded and improperly balanced vehicles are one of the leading causes of road accidents involving recreational vehicles and tow setups. Yet many drivers remain unaware of just how easy it is to exceed a legal or safe limit.

This article explains the technical side of vehicle and trailer weights, why it's critical to weigh your full setup, and how mobile weighing services provide detailed data such as individual axle loads and load distribution to help you stay within the legal and safe operating envelope.

Understanding the Key Weight Terms

To properly assess your vehicle or towing combination, you need to understand several technical weight terms. These aren't just theoretical—they’re regulated figures with legal and engineering significance.

Tare Weight: The unladen weight of a vehicle or trailer as delivered from the manufacturer. It excludes payload such as water, fuel, luggage, or passengers.
Gross Vehicle Mass (GVM): The maximum allowable weight of the vehicle when fully loaded, including passengers, fuel, accessories, and cargo.
Gross Trailer Mass (GTM): The total weight of the trailer on its wheels when hitched to the tow vehicle.
Aggregate Trailer Mass (ATM): The maximum allowable total weight of the trailer when it is not coupled to a vehicle (i.e., includes the tow ball load).
Gross Combination Mass (GCM): The maximum allowable combined mass of the vehicle and trailer when loaded to their respective GVM and ATM limits.
Tow Ball Mass (TBM): The downward force the trailer exerts on the tow hitch. Incorrect TBM can cause instability, poor handling, and suspension strain.
Payload: The difference between GVM and Tare weight. This is the total weight of everything you add to the vehicle—gear, accessories, passengers, etc.

Axle Weights: The Often Overlooked Metric

Even if your vehicle is under its GVM, you may still be overloading an axle—a serious safety and mechanical issue. Axle limits are specified by the manufacturer and can vary between the front and rear axles.

For example:

Rear axles on 4WDs and other vehicles are commonly overloaded due to dual battery systems, fridges, drawer setups, and full cargo areas. But the main reason is that when there is a tow ball added, the weight on the rear axle is severely increase due to the Leverage Effect (read below).
Caravans with uneven loading (e.g., water tanks or toolboxes on one side) can exceed one side’s suspension or axle rating, causing tyre wear, instability, or even axle damage.

Mobile weighing services use four or more precision pads to measure:

Individual wheel weights
Left vs right distribution
Front and rear axle loads
Tow ball download

This level of detail goes far beyond what static weighbridges offer, allowing for targeted load redistribution and pinpointing unsafe or illegal configurations before you hit the road.

Leverage Effect & How it can affect axles on your vehicle and caravan GTM and Tow Ball

The leverage effect plays a significant role in how weight is distributed across your vehicle’s axles and your caravan’s chassis. When a caravan is hitched to a tow vehicle, the tow ball weight (TBM) acts like a lever, applying downward force behind the rear axle. This creates a fulcrum effect, shifting weight from the front axle to the rear axle of the tow vehicle. Even a moderate TBM—say, 250–350 kg—can cause the rear axle to exceed its rated capacity by up to 160% or even more, while simultaneously reducing load on the front axle by 60% or sometimes more, which can degrade steering responsiveness and braking efficiency. On the caravan side, the leverage created by how cargo is loaded in front or behind the axle group directly affects the GTM (Gross Trailer Mass). If heavy gear is stored too far forward (in toolboxes or front water tanks), the tow ball mass increases, elevating both the TBM and the load transferred onto the rear of the tow vehicle. Conversely, weight placed too far back may reduce TBM but increase sway risk. Understanding and managing the leverage effect is essential to achieving balanced axle loads and safe towing dynamics.

LEVERAGE EFFECT CAN BE BEST UNDERSTOOD ON YOUR SETUP BY BEING WEIGHED BY A PROFESSIONAL MOBILE WEIGHING SERVICE

Why Accurate Weighing Matters

1. Legal Compliance

In Australia, and many other countries, driving a vehicle that exceeds GVM, ATM, or GCM is illegal. It may:

Result in fines
Invalidate your insurance
Lead to a defect notice or vehicle grounding

Some states conduct roadside compliance checks targeting caravans and trailers, especially during peak holiday periods. If you're found to exceed your legal weight limits—or your axle limits—you may be ordered off the road immediately.

2. Vehicle Safety and Control

An overloaded or imbalanced setup affects:

Braking distance: Overweight vehicles can increase braking distances significantly.
Suspension performance: Load beyond spec leads to sagging, bottoming out, and shock absorber fatigue.
Stability and sway: Incorrect ball weight or uneven side-to-side load distribution is a leading cause of trailer sway and vehicle instability.

3. Protecting Your Investment

Your tow vehicle or motorhome is a significant investment. Overloading accelerates wear and tear, particularly on:

Tyres (overheating, blowouts)
Transmission (especially automatics under towing strain)
Bearings and axles (particularly for off-road trailers)
Braking systems (increased heat and premature wear)

Additionally, many aftermarket additions—roof racks, awnings, water tanks, bull bars, and winches—add up quickly. Without weighing, it's impossible to know their full impact on your GVM or axle loads.

Why Mobile Weighing Services Are the Gold Standard

Unlike traditional public weighbridges, mobile weighing services bring the equipment to your location and provide a full breakdown of your vehicle’s weight profile. They are increasingly used by:

Caravan and RV owners
Fleet managers
Boat trailer operators
4WD enthusiasts preparing for remote travel

Mobile weighing typically includes:

Total GVM and ATM
Tow ball mass
Individual axle loads
Left/right side balance
GCM check
Compliance report with recommendations

This precise data enables owners to make informed decisions about:

What to remove or reposition
How to pack more evenly
Whether a GVM upgrade is needed
If their towing setup is legally and mechanically sound

Real-World Example: A 4WD & Caravan Combo

Let’s say you have:

A 4WD with a GVM of 3,200 kg and GCM of 6,000 kg
A caravan with an ATM of 2,800 kg

After loading up for a trip, you weigh your setup:

4WD weighs 3,100 kg – under GVM ✅
Caravan ATM = 2,750 kg – under limit ✅
GCM = 5,850 kg – under GCM ✅

But the mobile weighing service reveals:

Rear axle on the 4WD is 1,950 kg, but the axle limit is 1,850 kg ❌
Tow ball mass is 320 kg, affecting steering and front axle load
Left side of caravan is 200 kg heavier than the right

Even though all the major figures appear within limits, you’re still operating illegally and unsafely—and wouldn’t know it without axle-by-axle weighing.

Final Thoughts

If you travel with a caravan, boat, trailer, motorhome, or fully loaded 4WD, a comprehensive understanding of your weight profile is non-negotiable. It's not enough to "guesstimate" or rely on manufacturer figures—every setup is different, and every kilogram counts.

Mobile weighing services provide a level of insight and precision that static weighbridges simply can’t offer. They are a small investment for peace of mind, compliance, and—most importantly—safety.

So before your next big trip, take the time to weigh everything properly. You'll drive away more confident, more compliant, and better prepared for the road ahead.