zaro

How to calculate GCM?

Published in Vehicle Weights & Measures 3 mins read

The Gross Combination Mass (GCM) is accurately calculated by adding the Gross Vehicle Mass (GVM) of the truck to the Gross Trailer Mass (GTM) of the trailer being towed.

Understanding Gross Combination Mass (GCM)

The Gross Combination Mass (GCM) represents the maximum total weight allowed for a loaded towing vehicle (such as a truck or car) and its attached loaded trailer or trailers. This vital measurement ensures that the combined weight does not exceed the vehicle manufacturer's design limitations, which is crucial for safety and preventing damage to the vehicles and infrastructure.

The Simple GCM Calculation Formula

Calculating GCM is straightforward and follows a simple additive formula:

GCM = Gross Vehicle Mass (GVM) + Gross Trailer Mass (GTM)

Let's break down the components involved in this calculation:

  • Gross Vehicle Mass (GVM): This is the maximum loaded weight of the towing vehicle itself. It includes the vehicle's empty weight, fuel, occupants, and any cargo carried within the vehicle. For a truck, this is the maximum permissible loaded weight of the truck on its own.
    • Learn more about Gross Vehicle Mass (GVM).
  • Gross Trailer Mass (GTM): This refers to the maximum permissible weight that can be supported by the trailer's axles when it's fully loaded and coupled to a towing vehicle. It includes the trailer's empty weight and its cargo, but does not include the portion of the weight that rests on the tow ball (which contributes to the towing vehicle's GVM).
    • Find detailed information on Gross Trailer Mass (GTM).

Practical Example of GCM Calculation

To illustrate the calculation, consider a typical scenario directly from vehicle specifications:

Imagine you have:

  • A truck with a GVM of 5000 kg. This represents the maximum weight the truck itself, when fully loaded with its own cargo and passengers, is allowed to be.
  • A trailer being towed with a GTM of 3000 kg. This is the maximum weight the trailer, fully loaded, exerts on its own axles.

To find the GCM for this combination:

GCM = GVM of Truck + GTM of Trailer
GCM = 5000 kg + 3000 kg
GCM = 8000 kg

This calculation indicates that the total combined weight of this truck and its loaded trailer must not exceed 8000 kg to operate safely and legally.

Quick Reference Table: Key Weight Terms

Term Definition Example (Calculated or Capacity)
Gross Combination Mass (GCM) The maximum total loaded weight of a towing vehicle and its attached trailer(s). 8000 kg
Gross Vehicle Mass (GVM) The maximum loaded weight of the towing vehicle itself (truck, car, etc.). 5000 kg
Gross Trailer Mass (GTM) The maximum loaded weight supported by the trailer's axles when coupled to a towing vehicle. 3000 kg

Why Knowing Your GCM Matters

Understanding and adhering to GCM limits is paramount for several reasons:

  • Enhanced Safety: Operating within GCM limits ensures optimal braking performance, stable handling, and prevents excessive strain on tires and vehicle components, reducing the risk of accidents.
  • Legal Compliance: Exceeding specified GCM limits is illegal in most jurisdictions, potentially leading to substantial fines, loss of insurance coverage, and even vehicle impoundment.
  • Vehicle Longevity: Respecting GCM limits prevents undue stress on the vehicle's engine, transmission, braking system, and suspension, which significantly contributes to extending its operational lifespan.

Always consult your vehicle and trailer manufacturer's specifications, along with local traffic regulations, to ascertain the precise GCM limits applicable to your specific towing setup. Reputable sources, such as official government transport departments or established automotive associations, can provide comprehensive guidance.