How To Weight Your Car and Caravan To Make Sure You’re Compliant

Travelling overweight is one of the fastest ways to turn your big lap dream into a nightmare. Hefty fines, insurance issues, and dangerous handling are just the start. Yet many travellers hit the road without ever properly weighing their setup.

Getting an accurate weight isn’t just about compliance. It’s about safety, legal protection, and peace of mind. The process might seem daunting, but it’s simpler than you think when you know the right steps.

Here’s exactly how to weigh your car and caravan properly, understand what the numbers mean, and ensure you’re road-legal before you leave home.

1. Understand the Key Weight Limits

Before you drive onto any weighbridge, you need to know what numbers matter. Your compliance depends on five critical weight limits, and exceeding any one of them makes you illegal.

Gross Vehicle Mass (GVM) is your car’s maximum legal weight when loaded. This includes passengers, luggage, fuel, water, and your towball weight. Check your car’s compliance plate or manual for this number.

Gross Trailer Mass (GTM) is your caravan’s maximum legal weight when hitched and ready to travel. This is the weight on the caravan’s wheels only, not including what’s pressing down on your towball.

Gross Combined Mass (GCM) is the maximum legal weight of your entire setup: car plus caravan together. This is often the most restrictive limit and catches many travellers off guard.

Axle limits apply to each individual axle on both your car and caravan. These are often forgotten but just as legally binding as the total weights.

Towball capacity is how much downward force your towbar can handle. This isn’t just about the towbar itself but also your car’s rear axle capacity.

2. Find a Suitable Weighbridge

Not all weighbridges suit caravan weighing. You need one that can accommodate your combined length and provide separate readings for different parts of your setup.

Public weighbridges at waste transfer stations work well for basic total weight checks. They’re usually $10-15 per weigh and can handle long combinations. However, they often can’t separate your car from caravan weight or provide individual axle readings.

Truck stops with weighbridges offer better facilities. Many can separate your weights and some have segmented scales for individual axle measurements. Expect to pay $20-30 per session.

Caravan dealerships sometimes offer weighing services using portable wheel scales. This gives you the most detailed breakdown but may cost $50-100. The advantage is getting expert interpretation of your results.

Call ahead to confirm they can handle your setup length and ask about their weighing capabilities. A 30-metre combined length needs a weighbridge that’s at least 20 metres long to get accurate readings.

3. Prepare Your Setup for Weighing

Accurate weighing requires your setup to be loaded exactly as you’ll travel. This means everything you’d normally carry, positioned where you’d normally keep it.

Fill your fuel tank completely. A half-empty tank can throw your readings off by 40-60kg, which might push you over a weight limit you thought you were safely under.

Load all water tanks to your normal travelling level. Many people travel with full tanks, but if you typically run with tanks at 50% or empty them for weight reasons, weigh accordingly.

Include all passengers who’ll be travelling. Their combined weight affects both your GVM and weight distribution. If family members can’t attend the weighing, add 75kg per adult and 35kg per child to your final readings.

Pack your normal gear in its usual positions. Random placement can affect weight distribution and give you false confidence about your loading. Your mountain bikes, generator, and camping chairs should be exactly where you’d put them for travel.

Check tyre pressures and ensure they match your normal travelling pressures. Under-inflated tyres can affect weighbridge readings by several kilograms per wheel.

4. Weigh Your Car and Caravan Separately

Start by weighing your loaded car without the caravan attached. Drive onto the weighbridge with just your car, ensuring all wheels are on the platform but no part extends beyond the edges.

Record this weight as your loaded car weight. Compare it against your car’s GVM to see how much margin you have. This number becomes crucial when you factor in towball weight later.

Next, weigh your loaded caravan with the jockey wheel down and unhitched. Position the caravan so all wheels are on the weighbridge platform. Some weighbridges can’t accommodate caravan length alone, so you might need to include the jockey wheel.

This gives you the caravan’s total weight including the mass that would normally press on your towball. Note this number but don’t compare it directly to GTM yet since GTM excludes towball weight.

If the weighbridge operator can provide individual axle weights for your caravan during this weigh, request them. Uneven axle loading is common and can cause handling problems even when total weight is legal.

5. Weigh the Combined Setup

Hitch your caravan and drive the entire combination onto the weighbridge. Ensure both car and caravan wheels are on the platform and the outfit is sitting level as it would on the road.

This combined weight must not exceed your GCM limit. For many setups, GCM is the most restrictive limit and determines how much gear you can actually carry.

The combined weight should equal your separate car weight plus your separate caravan weight. If there’s a significant difference (more than 20-30kg), something’s wrong with one of your measurements or your setup has shifted.

If the weighbridge can provide separate front and rear axle weights for your car while hitched, request these. The rear axle weight will be higher than when unhitched due to towball weight transfer.

Some advanced weighbridges can tell you the towball weight directly by comparing your car’s rear axle weight hitched versus unhitched. If this service is available, use it for the most accurate towball measurement.

6. Check Individual Axle Weights

Individual axle compliance is often overlooked but equally important. Each axle on your car and caravan has a maximum weight rating that can’t be exceeded regardless of total weight.

Your car’s front axle weight should be similar hitched and unhitched. The rear axle will increase by roughly your towball weight when the caravan is attached. Both must stay within their individual limits.

Caravan axle weights should be reasonably balanced unless your van is specifically designed with different ratings per axle. A 200kg difference between axles suggests poor loading and potential handling problems.

If axle weights aren’t available from the weighbridge, you can estimate towball weight by subtracting your unhitched car weight from your hitched car weight. This difference mostly appears on the rear axle.

For twin-axle caravans, individual axle weights help identify loading problems. Heavy items placed too far forward or back create imbalances that affect tyre wear and road handling.

7. Calculate Your Compliance Margins

Now comes the crucial step: determining exactly how compliant you are and how much loading margin remains for future trips.

GVM compliance: Add your car’s weight plus towball weight, then compare to GVM. Your towball weight is roughly the difference between hitched and unhitched car weights.

GTM compliance: Your caravan’s GTM is its wheel weight only. Subtract estimated towball weight from your unhitched caravan total to get wheel weight, then compare to GTM limit.

GCM compliance: Your combined weight must not exceed GCM. This is often your most restrictive limit, especially with heavy caravans and loaded cars.

Axle compliance: Check that no individual axle exceeds its rating. Car rear axle gets loaded by towball weight, while caravan axles should be reasonably balanced.

Calculate your margins for each limit. If you’re within 100kg of any limit, consider that essentially at capacity since gear loads vary between trips and weighbridge accuracy has tolerances.

Common Weighing Mistakes to Avoid

Most weighing errors come from inconsistent setup or misunderstanding what the numbers mean. These mistakes can leave you thinking you’re compliant when you’re not.

Weighing with different fuel levels is the biggest error. A full tank versus half-empty can change your total weight by 60kg or more. Always weigh with tanks as you’ll travel.

Forgetting passenger weights catches families regularly. Four people add 250-300kg to your setup. If they’re not present during weighing, add their weights to your calculations.

Misunderstanding GTM confuses many people. GTM is wheel weight only, not total caravan weight. You must subtract towball weight from total caravan weight to get the number that counts against GTM.

Ignoring axle limits while focusing only on total weights. You can be under GVM, GTM, and GCM but still illegal if an individual axle is overloaded.

Accepting borderline compliance as safe. Weighbridge accuracy, fuel consumption, and variable loading mean you need meaningful margins, not just technical compliance.

Not checking multiple loading scenarios leads to problems later. Your setup might be legal as weighed but overweight with full water tanks or when carrying extra gear for extended stays.