If you’re thinking about buying a caravan then one of the first questions you should ask is: how much weight can you legally tow?
Even though the answer isn’t a single number, there is a simple explanation: Your towing vehicle has four (4) separate weight limits that you need to take into consideration. These are:
1. Towing capacity
2. Tow ball capacity
3. Your tow vehicle’s weight limit (GVM)
4. The combined weight of your vehicle and what it’s towing (GCM)
Here’s a more detailed explanation about each of these…
…using the Isuzu MU-X as an example:
1. Towing capacity: The maximum weight you can legally have behind you
This one’s fairly simple:
Vehicle manufacturers specify a weight. And you’re never allowed to tow more than that.
Often this is stated as ‘braked’ towing capacity…
…this just means that whatever you’re towing has to have its own brakes too
So for example:
The Isuzu MU-X has a braked towing capacity of 3,000 kg.
[You’ll find your vehicle’s towing capacity in your manual, your compliance plate, or even a quick Google search]
So never tow anything heavier than this.
To find out if you can legally tow your caravan:
- The EASY option is to find out your caravan’s maximum weight (Aggregate Trailer Mass). You can find this on it’s compliance plate.
- The BEST option is to weigh your caravan when it’s fully loaded so you know EXACTLY how much it weighs.
The reason that this is the best option is that it will also check that you haven’t overloaded your caravan and exceeded its weight limit (ATM).
2. Tow ball capacity: The maximum weight your tow ball can legally handle
When you hook up a trailer some of its weight is transferred onto your tow vehicle.
This is known as tow ball download.
And, vehicle manufacturers specify a limit to the amount of tow ball download it can handle. This is the tow ball capacity.
The Isuzu MU-X has a tow ball capacity of 300 kg.
For find out the tow ball download for your caravan:
You will not find the weight for your caravan’s tow ball download written anywhere… because your tow ball download changes every time you load your caravan differently or empty your water tanks.
[The number written on your compliance plate will be either the tow ball download when empty, or its maximum]
The only way to know if you’re exceeding your car’s tow ball capacity is with a set of scales.
Now, the ‘Happy Hour Scientists’ will tell you that a caravan’s tow ball download is around 10% of its weight…
… but it can range between 8-12%
[and you can also vary it yourself depending on how it’s loaded]
So if you have a caravan that weighs 2,880 kg your tow ball download may sit anywhere between 230 kg – 350 kg… which means you can’t legally tow it.
That’s a big difference. That’s why it’s worth getting a set of ball scales (good ones are only about $70 from eBay)
The interesting thing about your tow ball download is that this weight isn’t just relevant for determining how much you can legally tow because of tow ball capacity…
…you need to use this weight twice because it adds onto your car’s weight limit too…
3. Cars have a weight limit (GVM): Your caravan’s tow ball download is part of it’s carrying capacity
Your vehicle has a legal weight restriction. This is known as its Gross Vehicle Mass (GVM).
So for example:
The Isuzu MU-X has a weight limit (GVM) of 2,750 kg.
[You’ll find your vehicle’s GVM in your manual, your compliance plate, or even a quick Google search]
So how much can you put in your car before you exceed this limit?
To do this you need to know your starting point… this is known as the vehicle’s dry weight or kerb weight.
The Isuzu MU-X has a kerb weight of 2,157 kg.
The amount of weight you can add to your car is the GVM – Kerb Weight
So this means:
The Isuzu MU-X has a maximum carrying capacity (payload) of 593 kg
Here’s where you need to get out a notebook and pen and add up the weight of whatever you plan to carry.
- Bull bar
- Roof racks
- Luggage, and
- THE TOW BALL DOWNLOAD
Using the MU-X example:
A full tank of fuel and you’ve got 548 kg left to work with.
Let’s say you weigh 80 kg… you’ve now got 468 kg left.
Let’s say that you do fall into the category of magically having a 10% tow ball weight. If you’re towing a 2,880 kg van, that’s 288 kg out of your car’s payload.
You now have 180 kg left.
So that you’re not towing illegally you’ll need to choose between:
- The wife and kids, or
- The bull bar, fridge, and roof racks
4. The amount of weight you can legally tow is also limited by the combined weight of your vehicle and what it’s towing (GCM)
Even though both your car has a maximum weight limit and so does your caravan, there’s also a limit to how much they are allowed to weigh when they’re added together.
The thing is:
Sometimes this combined weight limit (Gross Combined Mass, or GCM) is less than the sum of the car’s and caravan’s weight limits.
What does this mean?
Your car might be under it’s maximum weight, your caravan might be under it’s maximum weight… but together they can be over.
The Isuzu MU-X has a combined weight limit (GCM) of 5,750 kg.
[It’s one of the few vehicles that can be loaded to it’s max GVM vehicle weight of 2,750 kg and still be able to tow it’s full towing capacity of 3,000 kg without exceeding it’s GCM]
Not so much.
How much you can legally tow = GCM – Vehicle Weight
Here’s an example of how to work out how much you can legally tow for the Holden Colorado if it’s loaded to it’s vehicle weight limit (GVM):
GCM of 6,000 kg – GVM of 3,150 kg = 2,850 kg towing capacity
[So yeah, even though it’s marketed as having a 3,500 kg towing capacity it doesn’t mean that’s how much you can actually tow]
To work out how much weight you can legally tow it’s more than just using the vehicle’s towing capacity.
You must also take into consideration tow ball capacity, the vehicles weight limit (GVM), and also the combined weight of the vehicle and trailer (GCM).
Now, there’s other things that should be taken into consideration: your caravan’s weight restrictions and that cars also have axle weight restrictions.
They’re topics for another day…
Check out this article if you want to know how much weight you can put in your caravan?
Otherwise you might be interested in this one: How To Work Out Caravan Tow Ball Weight [3 Options]