Load Ratings… Explained

Get A Load Of This – Load Ratings Explained


Infographic explaining Gross Combinations Mass, Gross Vehicle Mass, and Payload.


Understanding Load Ratings for Your Vehicle’s Roof Rack

When it comes to using roof racks on your vehicle, there are two key factors that you must carefully consider. The first being the manufacturer’s maximum Roof Loading Capacity rating, often referred to as the Gross Combined Mass (GCM). The second is the load specifications provided by the roof rack or bar manufacturer.

Vehicle Manufacturer’s Roof Loading Capacity (GCM)

Your vehicle’s GCM defines the maximum weight your roof can bear, encompassing both the roof rack itself and everything you intend to carry on it. To find your vehicle’s specific GCM, you have a few options:

  • Consult your owner’s manual.
  • Contact your vehicle manufacturer directly.
  • Check a trusted source like Redbook, where you can search for your vehicle and find GCM details in the Dimensions section.

It’s important to note that GCM ratings can vary significantly among different vehicle models. For example, most 4WDs can handle up to 100kg, with a few exceptions rated at 150kg. Very few reach a capacity as high as 200kg, such as the 200 series Landcruiser.

Exceeding your vehicle’s GCM is a big no-no. It can lead to adverse effects such as increased fuel consumption and compromised payload capacity. It can even potentially cause damage to your vehicle’s axle, thus, void your insurance. So, always stick to the manufacturer’s specifications to stay safe and efficient.

Roof Rack Load Capacity

In addition to your vehicle’s GCM, you must consider the load specifications provided by the manufacturer of your roof rack or bars. These specifications can differ for on-road and off-road conditions, with off-road ratings typically being 50-75% of the rated on-road capacity. (Off-road here includes any non-sealed surfaces like gravel or sand).


LOAD RATING Calculators (By Roof Rack Manufacturer)

Some important points you should keep in mind


Warning: Never, under any circumstances, exceed the manufacturer’s specifications for your roof rack.

Doing so can result in property damage, personal injury, or worse.


Insurance Matters: Regardless of your insurance provider, any modifications to your vehicle, including roof racks, must comply with relevant roadworthy regulations. Failure to comply can lead to legal trouble and potentially void or reduce your insurance coverage.

Top-Heavy Dangers: A lower weight on your roof is better for vehicle stability due to a lower center of gravity. Overloading your roof rack can strain your vehicle and lead to chassis, suspension, and driveline issues. It can also cause increased fuel consumption. Roof racks are ideal for storing lightweight, bulky items.

Spread the Load: Better-quality roof racks distribute weight safely, both on and off-road. Gutter-mounted systems spread the weight along the entire length of the gutter, reducing the risk of a bent chassis, especially for dual cabs.

Keep it Low Profile: Installing your roof racks as close to your vehicle’s roof as possible has multiple benefits. It reduces wind drag, improves fuel economy, lowers the center of gravity, and allows for easier parking and clearance under low obstacles like trees.

Static vs. Dynamic Weight: Consider whether the load on your roof rack is static or dynamic. Dynamic ratings come into play when you’re navigating unsealed roads. Always stay within your vehicle’s Gross Vehicle Mass (GVM), payload, GCM, and towing capacity limits to avoid damage, accidents, and insurance issues.

Axle Ratings: Balance the weight in your vehicle. Avoid overloading the rear, which can strain the chassis. This is especially important for dual cabs with heavy canopies or tow balls.

Estimate the Weight: Make a list of everything in your vehicle and estimate their weights. Check your owner’s manual or a resource like Redbook for your vehicle’s GVM, payload, and GCM. Don’t forget to account for accessories and holders attached to your roof rack or tray. If you’re concerned about nearing the limits, visit a local weigh station for a precise measurement.


Term Definition
4WD Four-wheel drive, also called 4×4 (“four by four”) or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels .
Ball Weight Sometimes known as Drawbar weight, Ball Weight is the weight at the hitch. Most vans have a Ball Weight which is measured while the van is empty (tare weight), some vans even provide a maximum ball weight. GTM – Also known as Gross Trailer Mass.
GCM GCM stands for Gross Combination Mass, and is the maximum weight your vehicle (& everything in it) and what you are towing can be.
GVM GVM stands for Gross Vehicle Mass, and refers to the maximum weight your vehicle can be at any given time. It is the combination of your Tare Mass and Pay load
GTM Gross Trailer Mass (GTM) is the maximum mass recommended by the manufacturer of your fully loaded caravan when it is hitched to your tow vehicle. The GTM of the caravan is transmitted to the ground by only the caravan tyres and excludes the mass distributed to the towing vehicle through the coupling.
On-Road On-Road refers to the load rating of a vehicle when traveling on a sealed road.
Off-Road Off-Road load rating refers to a vehicle traveling on an unsealed road that does not contain a surface protection layer.
Pay Load Your pay load is the amount of weight you can add to a standard vehicle before it becomes illegal. Anything that is necessary for the operation of the vehicle is part of the tare mass, and anything above this is part of your pay load.

This includes the weight of your passengers, the tow ball weight of a trailer (if you are towing) and all of your accessories and luggage. This is a very important piece of knowledge for those who own a 4WD.

Tare Weight Tare weight refers to the unladen weight of your vehicle, with only parts that are necessary for operation of the vehicle. It does not include any aftermarket accessories.

NOTE: Some car manufacturers do not include the aircon & fuel in the Tare calculation.

Towing Capacity Every vehicle comes with a set towing capacity. Anything you tow must be under this weight. Be sure you factor into account whether the trailer has brakes or not!