Gross Trailer Mass (GTM)
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Everything You Need to Know About Gross Trailer Mass (GTM)
In the towing and transportation industries, understanding the specific weight limits of your trailer is vital for safety, performance, and legal compliance. One of the key terms you’ll encounter is Gross Trailer Mass (GTM). This comprehensive guide will explain what GTM is, why it is important, how it is calculated, and the implications of exceeding it.
For the purpose of this article, “Trailer” refers to a caravan, horse float, or any other trailer.
What is Gross Trailer Mass (GTM)?
Gross Trailer Mass (GTM) refers to the maximum allowable weight of a trailer when it is fully loaded, excluding the weight imposed on the tow vehicle’s hitch (Tow Ball Mass – which is included in the Gross Vehicle Mass GVM or Aggregate Trailer Mass ATM calculation). In other words, GTM represents the downwards pressure exerted on the axle/group of the trailer when connected to the tow vehicle, including any cargo, fluids, and additional accessories. When combined with your Gross Vehicle Mass (GVM), this represents your Gross Combined Mass (GCM) calculation.
When assessed by Weigh My Ride, the Tow Ball Mass will be captured at the tow coupling using specialised, purpose built weighing equipment, not at the jockey wheel. This ensures the most accurate measurement.
Importance of Gross Trailer Mass
1. Safety
Adhering to the GTM is crucial for ensuring the safe operation of both the trailer and the towing vehicle. Exceeding the GTM can lead to:
- Reduced braking efficiency and increased stopping distances.
- Poor handling and increased risk of trailer sway.
- Strain on the trailer’s axles, suspension, and tyres.
2. Legal Compliance
Operating a trailer that exceeds its GTM can result in fines, penalties, and legal liabilities. Moreover, in the event of an accident, insurance claims may be denied if the trailer was overloaded.
3. Trailer Longevity
Consistently operating a trailer within its GTM helps maintain the longevity of the trailer. Overloading can cause excessive wear and tear on essential components, leading to more frequent repairs and reduced lifespan.
Components of Gross Trailer Mass
- Tare Mass: The tare mass is the weight of the empty trailer, as it was at the time of manufacturing including any batteries, solar panels etc that formed part of the original build specification. The tare calculation excludes fluids, cargo and additional accessories.
- Payload: Payload refers to the weight of the cargo that the trailer can carry. This includes all fluids, goods, equipment, and additional accessories loaded onto the trailer.
- Axle Load Capacity vs GTM: The trailer GTM is different to the axle/group load capacity. Whilst the axle load capacity will likely be rated higher than the GTM specification, it is very important not to exceed the maximum allowable GTM.
- Tow Ball Mass: The trailer tow ball mass is the downwards mass exerted on the tow vehicle tow ball and is not included when calculating GTM.
Calculating GTM
Calculating GTM involves adding up several components to ensure the total weight does not exceed the manufacturer’s specified limit:
- Determine the Tare Mass: Find the tare mass of your trailer, which is typically listed on the compliance plate or in the manufacturer’s documentation. IMPORTANT NOTE: Tare mass listed on a trailer compliance plate can be different to actual tare weight. It is recommended to have your tare weight validated prior to loading or adding accessories.
- Add the Payload: Include the weight of all fluids, cargo and additional accessories loaded onto the trailer.
- Subtract the Tow Ball Mass: Confirm the trailer tow ball mass (TBM) and exclude this from the calculation.
GTM = Tare Mass + Payload (inc Fluids) – Tow Ball Mass (TBM)
Ensuring Compliance with Gross Trailer Mass
- Regular Weighing: Regularly weighing your trailer ensures it remains within the specified GTM. Services like Weigh My Ride offer professional weighing solutions to provide accurate measurements and peace of mind.
- Proper Loading Techniques: Distribute the load as evenly as possible within the trailer to maintain balance and stability. The target tow ball mass is approximately 10% of the actual ATM. Consider the position and impact of full water tanks as this can have a significant impact on tow ball mass and balance.
- Routine Maintenance: Regular maintenance checks are crucial to ensure all components of the trailer and towing vehicle are in good working order. This includes inspecting tyres, brakes, suspension, and couplings. It is common for couplings and tow balls/pins to come loose over time or not be tightened to the correct torque setting upon installation. This requires a special torque wrench – not a traditional shifter or alike.
- Adhering to Manufacturer Guidelines: Always follow the manufacturer’s guidelines regarding the maximum load capacities and GTM. These guidelines are based on extensive testing and are designed to ensure safe and efficient towing.
Choosing the Trailer for Your Needs
When selecting a trailer, consider its GTM in relation to your needs:
- Purpose and Usage: Choose a trailer with a GTM that suits the type of cargo you intend to carry. For heavy or bulky loads, ensure the trailer has a higher GTM. Don’t forget to include fluids such as gas, fuel and water in this calculation.
- Future-Proofing: Anticipate any future increases in load requirements (such as a bike rack or additional solar panels/batteries) and select a trailer with a GTM that provides a margin for additional weight.
- Professional Advice: Consult with trailer manufacturers or experts to ensure the chosen trailer meets your specific needs and complies with the specifications of your towing vehicle.
Conclusion
Understanding Gross Trailer Mass (GTM) is essential for anyone involved in towing. Adhering to the specified GTM ensures the safety, performance, and longevity of both the trailer and the towing vehicle. Regular weighing, proper loading techniques, routine maintenance, and compliance with manufacturer guidelines are crucial practices for staying within the GTM limits.
At Weigh My Ride, we provide professional towing assessment and weighing services to help you accurately measure and manage your trailer’s weight, ensuring compliance with GTM regulations. Whether for personal or commercial use, understanding and respecting your trailer’s GTM is key to safe and efficient towing.