When Towing a Caravan, Why Is It Important to Know Your Water Weight?
Manufacturers have established weight limits for each caravan and towing vehicle.
To tow legally and safely, you must first understand these weights and then how the water you have on board will affect towing.
First and foremost, here are the important weights and prices to be aware of when purchasing or renting a caravan.
1. Vehicle Towing Capacity
Before going out to look at caravans, you should know how much weight your vehicle can pull. This weight is referred to as towing capacity, and there are two rates:
Braked Towing Capacity
The maximum weight that a vehicle can haul with an independent braking system on the trailer. The trailer's braking system will be connected to your vehicle through a cable.
Unbraked Towing Capacity
The maximum weight that a vehicle can haul without using an independent braking mechanism on the trailer. Because the towing vehicle must absorb the majority of the braking force, this rating is usually substantially lower than the braked towing capacity.
Towing capacity rates can be found in your vehicle's owner's manual, on a label on the driver's side door jamb, or by searching online for the make and model's towing capability.
The total combined weight of the whole towing set-up, including the trailer and its full load (including water), PLUS everyone and everything you intend to convey within the towing vehicle, must not exceed the manufacturer's towing capacity rate. Attempting to haul more than your vehicle's stated towing capability will stress your engine, damage your gearbox and back axle, and endanger you, your passengers, and other road users.
2. Towbar Rating
Once you know your vehicle's towing capability, double-check that the towing hitch installed on it can also carry this maximum weight because towbar maximum towing weights can vary. If your car's towing capacity is 3000kg, but your towbar is only rated for 2500kg, you can only tow up to 2500kg securely. You can only pull 2800kg if the towbar is rated at 3000kg, so your car's towing capacity is just 2800kg.
3. Weights of Towing Vehicles
Kerb Weight: This is the weight of an empty car with a full fuel tank but no passengers, luggage, or installed extras like bull bars or roof racks.
Gross vehicle mass (GVM): This is the sum of the vehicle's kerb weight plus the passengers, luggage, and extras it carries.
Tare weight: This is the dealer-supplied unladen vehicle weight with only 10 litres of petrol in the tank.
Gross combination mass (GCM): The official maximum total weight allowed for both the towing vehicle and the trailer is known as Gross Combined Weight Rating (GCWR) or Combined Vehicle Mass (CVM). It's the sum of the GVM of the vehicle and the Aggregate Trailer Mass. (ATM).
4. Trailer Weights
Tare weight: This is the unladen weight of the trailer or caravan as specified by the dealer. This is the vehicle’s overall weight without any load, such as water in the tanks, gas bottles, personal possessions, or fitted equipment like an awning or air conditioner. ATM (aggregate trailer mass): When uncoupled from a vehicle, the trailer's tare weight plus its maximum payload, including water, gas cylinders, luggage, personal belongings, and accessories, is referred to as gross trailer weight (GTW).
Gross trailer mass (GTM): When a fully loaded trailer is connected to the towing vehicle, the weight it exerts on its own axle will be less than the ATM since some of the trailer's weight will be transmitted to the towing vehicle.
5. Towball Weight
Towball weight, also known as tow ball loading or downward force/weight, is the greatest vertical weight that may be applied to the tow ball without lifting the front wheels of the towing vehicle and limiting its ability to steer and brake correctly. The towing capacity of front-wheel-drive cars is lower than that of rear-wheel-drive and all-wheel-drive vehicles. Towing capacity is also determined by tow ball weight. Even if a trailer is lighter than the stipulated towing capacity, it can exceed the tow ball loading rate if it is too front heavy.
6. Water Weight
We need to look at the water now that we've covered the weights and rates that go into determining the maximum weight your truck, vehicle, or SUV can pull. Knowing how much your caravan weighs with full water tanks is crucial and how onboard water affects towing safety. Most modern caravans include two or more enormous water tanks, with some larger versions having as many as four. These tanks will typically accommodate 60-90 litres and will be used to store fresh, grey, and black water.
You don't need to be a rocket scientist to figure out that one litre of water weighs one kilogram. Therefore water weight can quickly deplete your vehicle's towing capacity.
Also, if your water tanks are near the front of the trailer, they can affect your tow ball loading if the trailer is too front-heavy. Most manufacturers place tanks over or just ahead of the axle or axle group so that any additional mass aids in maintaining the van's forward balance in terms of ball weight.
Full water tanks increase towing comfort and fuel economy by a significant weight and impact ball weight. On the other hand, travelling with empty water tanks is risky, especially if you don't know if you'll be able to fill up at your destination. When travelling to isolated places, you can't afford to be without water. How can you figure out how much water you'll need on the road? When pulling a caravan, is it better to have full, empty, or half-full water tanks? Beyond the weight of water, we must consider the effect of fluid movement on towing sway.
Water Wobbles
Water is an easy-to-move fluid that 'washes' back and forth and side-to-side with the movement of the travelling vehicle. Caravan water tanks are often composed of blow-moulded or roto-moulded plastic with internal baffles to reduce liquid surge when in motion.
If the tank is only partially filled, splashing and rolling the liquid in the cartage tank when stopping, starting, and taking turns can cause dangerous surges within the tank, making control of the trailer uncertain for the driver. When towing, an empty tank won't be a problem, and a full tank, while hefty, will be pretty stable, but half-filled tanks can cause your van to sway due to the force of the water shifting across its axis.
Getting the Right Balance
Before you embark on your next caravan trip, think about how much water you'll need in your tanks based on what you'll be doing and where you'll be going.
Because water is a survival necessity, it's critical to keep adequate supplies on hand when going into remote or isolated regions.
If you know, there will be water access points throughout your journey, or at your stopping spots. However, you may want to travel with empty tanks and fill them up when you arrive. Consider isolating connected tanks so that one is empty and the other is full, rather than having two half-filled tanks while on the road. Before you go, inquire if any of your other campers want to help you fill up on freshwater so you can travel light.
Final Thoughts
Keeping track of your trailer load and water weight is a time-consuming but crucial element of caravan safety. Thankfully, contemporary weighbridges can quickly and efficiently perform all of the towing weight calculations and print off a copy for you to keep on hand.