In this ultimate guide to towing series, Robert Pepper discusses caravan weights, including vehicle and towing weights, limits, how to weigh your rig, and important things to consider.
I’m sorry that you have to read this. It’s technical, tedious and you just want to get going with your new caravan or camper trailer. But your caravan or trailer needs to be weight-compliant, so I’ll make this as quick and simple as I can. Yet I’m pretty confident it’s the most comprehensive guide on this topic. I’ve been writing about it for years and was the first to highlight the “3,500kg tow” problem that everyone now knows about.
You’ve probably never needed to worry about how heavy your car is before you began towing, but unfortunately, in today’s world, many vehicles run close to, and even over their various weight limits. That has implications for matters such as insurance, warranty, safety and vehicle wear.
For any given weight there is the limit, and what the weight actually is. The two are often confused. For example, the maximum a vehicle can weigh is its GVM, or Gross Vehicle Mass, and what the vehicle weighs is its Vehicle Weight, which should never exceed the GVM. You don’t weigh a vehicle and say, “that’s its GVM”. You weigh for the vehicle weight and see if that’s less than GVM.
We’ve listed the actual weight terms in the summary table below. Note that for some terms like GVM, there is an industry-standard. However, for others, like the maximum the car can tow, there is not.
Vehicle weights & limits
| Terms for actual weight | Description | Terms for Weight Maximum Limit | Where to find your limit |
| Unhitched Car Weight | How much your vehicle weighs. It is best to note in what state of load this is, for example, unladen, or ready for a trip etc. | GVM – Gross Vehicle mass | Vehicle weight placard near the front door jamb, owner’s manual, carmaker website – make sure it is specific to your vehicle and not general. |
| Front axle | The weight of the vehicle on the front axle. | Front axle limit | Owner’s manual, carmaker website – be careful it is specific to your vehicle and not general |
| Rear axle | The weight of the vehicle on the rear axle. | Rear axle limit | Owner’s manual, carmaker website – be careful it is specific to your vehicle and not general |
Note: all three weights differ when a caravan or trailer is hitched up. The load (weight) on the rear axle increases, the load on the front axle decreases, and vehicle weight increases. However, the limits remain the same.
Towing weights & limits
If you’re towing, then there’s a few more weights and limits to consider:
| Term for actual weight | Description | Term for Weight Maximum Limit | Where to find your limit |
| Total Caravan Weight (1) | The maximum the towcar can tow, assuming the trailer has brakes. There is a lower limit for trailers without brakes, but almost all caravans will exceed that limit so we won’t focus on it. | Braked Tow Capacity | Vehicle owner’s manual. |
| Total Caravan Weight (2) | How much the trailer weighs. As with Unhitched Car Weight, make a note of what sort of load the trailer has; unladen, big trip, short trip etc. The weight of the caravan must be less than or equal to the Braked Tow Capacity AND then ATM, and you work off whichever is the lower figure as your maximum. | ATM – Aggregate Trailer Mass | On the trailer’s placard on or near the drawbar. |
| Caravan Axle Weight | The weight on the trailer’s axles, so this excludes the towball mass. | GTM – Gross Trailer Mass | On the trailer’s placard on or near the drawbar. This is always less than the ATM. |
| Tow Ball Mass and % | The weight placed on the towball by the trailer in kilograms, and as a percentage of the trailer’s mass. Note that 10% TBM is often a maximum, and not something to aim for. The towcar maker will set a figure in kilograms and that is not to be exceeded. The percentage of TBM to trailer weight is not a formal limit, but the trailer maker may recommend a range. | Towball mass, or sometimes TBM, ball downforce. | The vehicle owner’s manual, OR towbar, or towbar tongue; whichever of the three is the least. The trailer maker may make a recommendation, but the actual maximum is set by the towcar’s limits. |
| Total Combination Weight | The maximum your vehicle AND trailer can weigh together. | GCM – Gross Combination Mass. | Owner’s manual, carmaker website – be careful it is specific to your vehicle not general. If it isn’t listed, then don’t worry about it. |
How do I weigh my rig?
There are three main options:
- General weighbridge
- GoWeigh weighbridge
- Specialised trailer weigh operator
The general weighbridge is any public weighbridge you can find such as at your local tip. Or there are some that are permanently open and free. They will weigh to the nearest 20kg, and you’ll need to know how to do the weigh such that you get all the results needed and write them down somewhere as you go. So it’s only for people with a good understanding of weights. You will also only get axle weights, not per-wheel.
The GoWeigh weighbridges are similar, but they have a specific trailer/caravan weigh process. This process steps you through what you need to do, and then you get a report emailed to you with all the results neatly in one place with the calculations done. However, that will tell you only what you weigh, not what the limits are. And like the general weighbridges, it’s to the nearest 20kg and per axle, not per wheel.
The specialised weigh operators are often mobile and will weigh your rig with sensitive scales, typically to the nearest 1kg, and on each wheel. They will also provide a detailed report specific to your rig, talk you through the limits, and provide personalised advice. But they are considerably more expensive as you’re paying for 1:1 time. Many people find the investment worthwhile and are repeat customers. There are many good operators, but some poor ones. You can find a list here including some tips on selecting a good one.
Here is a sample weigh operator report courtesy of Van Weigh:
So which to choose? All of them! When it comes to a real-world weigh, if you understand the weights, I’d use a general weighbridge or a GoWeigh. If you want a personal touch, everything explained and calculated for you, or highly accurate per wheel-weighing, then use the specialised operators. Or maybe start with an operator to get things explained, then once you’re comfortable, use a weighbridge.
Example weigh
Now, let’s run through an example weigh-and-check process. Here’s some data you may wish to collect, with examples:
- Vehicle GVM – example 3200kg
- Vehicle towball mass limit – 250kg
- Braked Tow Capacity – 2500kg
- Front axle limit – 1500kg
- Rear axle limit – 1850kg
- Trailer ATM – 2700kg
- Trailer GTM – 2600kg
- Vehicle GCM – 6000kg
Ideally, you should gather all that data before your weigh. But you can do it afterwards, and you don’t need all the data if you don’t need to check any specific limit.
Now, let’s walk through an example report from GoWeigh
The mobile operators will have something similar:
This report shows that the Total Caravan Weight is 2,300kg, which must not exceed the ATM of 2,700kg, so we’re 400kg under. The Braked Tow Capacity is 2,500kg, so we’re 200kg under that limit. The Unhitched Car Weight is 3,000kg, and that must not exceed the GVM of 3,200kg, so we’re 200kg under. The Caravan to Car Ratio is 77%; this means the trailer is 77% of the towcar’s weight. You want your towcar heavier than the trailer for stability, so less than 100% is good. Although that alone does not guarantee stability. There is no regulation or limit for that ratio.
The Unhitched Car Weight of 3,000kg is split 1,400kg on the Front Axle Weight, which is 100kg under the front axle weight limit of 1,500kg, and 1,600kg on the Rear Axle Weight which is 250kg under the rear axle limit of 1,850kg. The front/rear weight balance is 47/53% and is shown for those interested in vehicle dynamics. There’s no specific limit to worry about.
The Caravan Axle Weight (Total Caravan Weight minus Towball Mass) is 2,060kg and shows how much weight is on the axles of the trailer. That must not exceed the GTM of 2,600kg, so we’re 540kg under.
Now we hitch the car to the trailer…
Now we hitch the car to the trailer and that means we can calculate the Tow Ball Mass. It’s 240kg, which is close to our vehicle TBM limit of 250kg, noting the scales only report in 20kg increments. We also show the percentage of towball mass; in this case, it’s 10%.
We also have to add the Tow Ball Mass to the vehicle weight – so that’s now 3,000kg of car plus 240kg of towball mass = 3,240kg Hitched Car Weight. Unfortunately, that’s 40kg over the 3,200kg GVM. We’ll fix that later.
The axle weights have changed too. The Front Axle Weight has gone from 1,400kg to 1,320kg (yes, that’s 80kg less) so still under the 1,500kg limit. The Rear Axle Weight has gone from 1,600kg to 1,920kg, another 320kg – despite the fact we only added 240kg TBM. The effect of the TBM is that we’ve added 320kg to the rear axle but lost 80kg from the front axle, so the total corresponds to the 240kg Tow Ball Mass.
Finally, we can add the Total Caravan Weight to the Unhitched Car Weight to give us a Total Combination Weight of 5,300kg, which is 700kg under the GCM of 6,000kg.
We’ve exceeded two limits. What can we do about it?
So we’ve exceeded two limits; the GVM by 40kg, and the rear axle load by 70kg. What might we do? Well, it turns out there are two e-bikes on the drawbar and a few tools in a front box. We can relocate them inside the caravan over the axles, which doesn’t change the caravan weight, but it does reduce the towball mass. The generator is old and heavy, so that’s swapped out for a newer, much lighter version.
The fridge is carried in the van, but in a similar position to the e-bikes, a long way forwards of the van axles, so it adds to the TBM. So the fridge gets relocated into the vehicle, which also helps make the towcar heavier and the van lighter, which contributes to stability. All these changes reduce the TBM from 240kg to 160kg, with a consequent reduction in hitched vehicle weight and rear axle load.
However, we’ve added 50kg of fridge to the car and we’re trying to get the weight down as it’s close to its GVM. Lucky, there’s a few bags and tools we can relocate from the car to the centre of the van, and that is enough to drop the vehicle weight. The van has plenty of payload (difference between its weight and ATM) so it can take the load. But remember it’s better to have weight in the towcar than the trailer.
With the changes made, back we go for another weigh, and this time it’s within limits even though we’ve only reduced total weight by 20kg!
For more information on RV road safety, visit the rvSafe website, where you’ll find a number of great resources to help you remain safe on our roads.
