One of the most important aspects of towing is understanding the transfer of weight from the caravan or trailer onto the back of the tow vehicle. This is called ‘tow ball weight’ or ‘tow ball download.’
It’s equally important to understand that your tow ball weight is a fluctuating figure, which will change every time you add, subtract or rearrange your trailer load.
The acceptable tow ball weight (TBW) in Australia is about 10% of your trailer’s ATM (Aggregate Trailer Mass) or a maximum of 350 kg – whichever is lower.
This is where working out the right tow ball weight for your set-up can get a bit tricky because your tow ball weight won’t always stay as one set figure. However, there are still legal requirements around tow ball weights for optimum towing stability and safety.
Here’s how to measure all caravan towing weights so that you can get your full set-up sorted.
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Understanding Compliance Plate Tow Ball Weights
There are various terms that can be used on trailer and caravan compliance plates when it comes to tow ball weights.
Here are some common examples and what they mean.
Empty Ball Mass
This can also be known as ‘Ball Loading at Tare.’
Empty Ball Mass is the tow ball weight of the caravan when it was first manufactured before any load was added to it. This includes any accessories that were added after it left the factory, plus luggage, water and full gas bottles.
However, the Empty Ball Mass weight that’s stamped onto the VIN plate may not necessarily be 100% accurate for your trailer. Many manufacturers are known to only weigh one trailer or caravan from each batch and use those tare weights on all of the compliance plates for the entire batch.
In any case, the Empty Ball Mass becomes irrelevant once the caravan has left the factory and the first accessory is fitted.
Max Ball Loading
‘Max Ball Loading’ can also be written as:
- Tow Ball
- Maximum Permissible Ball Loading
Max Ball Loading is the recommended maximum ball weight when taking into account the caravan’s drawbar strength, as suggested by the manufacturer.
However, Max Ball Loading is not necessarily a strict legal requirement. In fact, many caravan compliance plates don’t even include Max Ball Loading.
How Much Should Your Tow Ball Weigh?
The most commonly used method in Australia for figuring out if you’re within your legal tow ball weight limit is by using the 10% rule.
The 10% rule says that your tow ball weight should be about 10% of your ATM or fully-loaded trailer, but must not exceed 350kg.
This figure is a little fluid and can actually range anywhere from 5 – 15%, depending on the length and weight of your trailer.
A good rule of thumb is to get as close to the 10% (a little either side is fine) for larger and heavier caravans. For camper trailers and compact vans, 5 – 15% is acceptable.
Do You Calculate Using ‘ATM’ or ‘Actual Fully-loaded’ Weight?
Your ATM (Aggregate Tare Mass) is the maximum weight that your trailer is allowed to be at any given time when fully-loaded. This weight is set by the manufacturer and must not be exceeded.
However, sometimes when the trailer is all loaded up for travel, it may actually weigh more or less than what that maximum ATM figure is.
Therefore, the first thing to check is that your trailer is under it’s ATM weight allowance, so that you know you’re legal there.
Ensure Your Trailer is Under its ATM Weight
You’ll need to hitch up your trailer and head to a public weighbridge. Step-by-step instructions are below for weighing your trailer.
How to Weigh Your Trailer:
- Ensure the trailer is fully-loaded for travel
- Drive the trailer onto the weighbridge and unhitch it from the car
- Drive the car off the weighbridge, leaving only the trailer on the scales
- Record the weight
- This needs to be lower than the manufacturer stated ATM
You need to make sure that the weight of your fully-loaded trailer does not exceed the ATM weight (which you can find stamped on your trailer compliance plate).
If you find that your trailer is overweight, then it’s time to cull some stuff until you can get it under that ATM weight.
Using the 10% Rule
Once you’ve made sure that your trailer is under it’s legal ATM weight, you should now also know what the ACTUAL weight of your fully-loaded trailer is.
For many people, being fully-loaded will take them right up to their ATM, which is perfectly fine. For others, they may come in under that ATM weight and have some payload to spare, which is even better.
Either way, you will need to use the actual weight of the fully-loaded trailer when using the 10% rule.
Remember, 10% of your trailer’s fully-loaded weight is an average. It’s acceptable to be a bit above or a bit below that if that’s what your set-up requires in order to stay level.
Use the Tow Ball Calculator below to get an estimate of what your tow ball weight should be.
Check Your Towbar Rating
With tow ball weights, it’s not just about getting the caravan or trailer right. You will also need to check how much weight your vehicle’s tow bar is rated to take.
The tow bar weight rating, as specified by the vehicle/ tow bar manufacturer, states the Max Ball Load and Max Trailer Weight that the tow bar is designed to carry.
This is another super important reason for making sure that you know what your tow ball weight is and that your tow bar is strong enough for the weight of your tow ball download.
| Example: |
|---|
| Your vehicle’s maximum ball load is 300kg. (i.e. you cannot tow anything with a tow ball weight higher than 300kg). You weigh your caravan and find its tow ball weight is 310 kg. Although the tow ball weight is legal for the caravan, it’s 10kg over for the vehicle’s tow ball. You need to reduce the caravan’s tow ball weight by at least 10kg. |
The last thing you want is to be involved in an accident only to find that your tow ball weight was too heavy for your tow bar and the insurance company says, “Too bad, so sad.” Or worse, someone ends up seriously injured due to your set-up being overweight in some capacity.
How to Reduce Tow Ball Weight
Distribute Your Load Strategically
The easiest way to understand the importance of tow ball weight is to imagine your caravan or trailer as a see-saw.
For optimum towing safety and stability on the road, your see-saw (caravan) needs to be as level as it can be with the weight inside distributed correctly.
It’s important to load the heaviest items as close to the caravan axles as possible, so that the axles can “carry” the load.
Heavy items include:
- Water (a well-designed caravan should have the water tanks placed around the axles)
- Food & drinks
- BBQ & cooking items
- Heavy camping gear
- Tools
- Generator
Lighter items are better off being loaded up high and at both ends of the caravan, so there’s less weight to tip the see-saw back (bringing the caravan nose up) or forward (putting too much weight over the tow ball).
Having said that, a caravan should be a bit heavier at the front than at the rear so that it doesn’t drastically sway, which can quickly escalate into jack-knifing.
A caravan that is overloaded at the ends will create ‘Yaw Inertia,’ also known as “caravan sway” or “caravan snaking.”
This is because the two heaviest areas are farthest away from the axles, which is the pivotal point. From there, the caravan will tend to increase in oscillation (back and forth rhythm) rather than being pulled into line by the force of the towing vehicle.
Use Ball Weight Scales
Once you’ve distributed your load evenly throughout the caravan (with the heaviest stuff being over the axles), it’s time to measure your tow ball weight. If you find that it’s too high, you’ll need to start playing around with the load.
The easiest way to reduce your tow ball weight is to have a set of Ball Weight Scales on hand so that you can physically play around with the load until you can get it right.
The benefit to having your own set of scales is that every time your load changes, you’re easily able to reweigh your tow ball and check that you’re all good.
Remember, every time you add to, subtract from or shift your load, the tow ball weight will change. This includes using water from the water tanks, eating through your food stash and even adding things that you purchase along the way.
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How to measure tow ball weight with Ball Weight Scales:
- Make sure your caravan is level
- Place wheel chocks under the caravan wheels to secure the van
- Raise the jockey wheel
- Place the Ball Weight Scale directly underneath the draw bar coupling
- Lower the jockey wheel until the full weight of the draw bar is on the scales
- The reading is your tow ball weight
If you don’t have a set of ball weight scales, below are two more options for weighing your tow ball weight.
Remove Weight off the Tow Ball
Another way to reduce tow ball weight is to simply remove weight from the front of the caravan. Sounds easy enough, right?
Not quite. You can’t just remove weight from the front and push it all to the back, because then the caravan’s tail end will become too heavy.
If the caravan is too light in the front (i.e. under its tow ball weight), there will be a drastic increase in the chance of trailer sway, as well as compromised braking and steering.
If you do decide to remove weight from the front of the caravan to reduce your tow ball weight, you will either need to remove those items completely or be strategic about where you shift them to.
This will probably be a process of swapping heavier things from the front for lighter items from elsewhere in the trailer.
You can also consider removing heavy tool boxes, bike racks, gas bottles and other accessories off the front of the caravan to reduce the tow ball weight.
Another consideration is to move some things from the caravan that could be stored inside the tow vehicle (if you have enough spare payload allowance there).
Empty the Water Tanks
It’s important to measure your tow ball weight with full water tanks, as well as the tow ball weight without there being any water in the tanks.
Just like full water tanks can push some caravans over their ATM, it can also put too much weight over the tow ball.
If travelling with full water tanks is the difference between your tow ball weight being within the safe 8 – 12% range or being over, then you will simply have to travel without water in the tanks.
There are a whole host of pros and cons for travelling with full vs. empty water tanks, which you can click below to read all about.
Record item weights with the Caravan Packing List below to help sort through your payload & towing weights.
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