The 3,500 kg towing capacity myth
A vehicle rated to tow 3,500 kg usually can't tow 3,500 kg and carry a full load at the same time. Here is why GCM, GVM, tow ball and axle limits get in first.
Facts checked
What "3,500 kg" actually promises
A braked towing capacity of 3,500 kg is a common headline figure for utes and large SUVs. It means one thing: the heaviest loaded trailer the manufacturer says the vehicle may tow.
It does not say the vehicle can tow that trailer while it is also full of people, fuel, water, a canopy, a fridge and a long-range tank. For that, other ratings come into play, and they usually bite first.
Put plainly, a vehicle's gross combination mass (GCM) may be less than its GVM plus its towing capacity. So you can often have a full trailer or a full vehicle, but not both.
RAC WA's view is blunter still. It calls the idea that 3,500 kg is easy for a modern SUV or dual cab ute "marketing hype", and points out that a 3.5-tonne trailer is almost certainly heavier than the vehicle towing it.
The limits that come before towing capacity
Towing capacity is only one of several limits. The loaded trailer must stay within all of these, and the lowest of them is the one that applies to you:
- the vehicle's towing capacity
- the towbar and coupling ratings
- the trailer's own ATM (see ATM vs GTM)
- the vehicle's GCM, if one is supplied
- the rated capacity of the tyres
On top of those, the vehicle itself has to stay within its GVM and its axle limits. Four of them work against a heavy trailer.
1. GCM
GCM is the most the vehicle and trailer may weigh together while hitched (see what is GCM). If GCM is less than GVM plus towing capacity, as above, then every kilogram you add to the trailer is a kilogram you can't carry in the vehicle, or the other way round.
2. GVM, and the tow ball's share of it
The tow ball load is carried by the vehicle, so it must be included as part of the vehicle's GVM. A heavy trailer has a heavy tow ball load, and that comes straight out of the vehicle's payload, on top of the people and gear you would otherwise carry. See what is GVM and payload.
3. The tow ball rating
The vehicle has a maximum tow ball mass. It is often taken to be 10% of the towing capacity, but many vehicles are rated differently, so check the figure for yours. LoadSavvy uses 10% only when nothing more accurate is available: it starts from your vehicle's published tow ball rating, or your own figure, and falls back to 10% of the towing capacity, labelled as derived, when neither is known. The towing rating includes both a trailer weight capacity and a ball weight capacity, and both must not be exceeded. A 3,500 kg trailer that wants more download than the vehicle allows is over a limit, even though it is within towing capacity. See tow ball mass.
4. The rear axle
The same tow ball load has a second effect. The tow ball sits behind the rear axle. That lever loads the rear axle by more than the tow ball load itself, and lifts some weight off the front axle. The rear axle can be overloaded even when the vehicle is under GVM. This is especially common in dual cab utes, where nearly all of the load space is behind the rear axle. See front and rear axle limits.
A made-up illustration
Here are the first three limits working together. These figures are invented to keep the arithmetic simple. They are not a real vehicle.
| Figure | |
|---|---|
| Vehicle, empty with fuel | 2,300 kg |
| GVM | 3,100 kg |
| GCM | 6,000 kg |
| Towing capacity | 3,500 kg |
| Tow ball rating | 350 kg |
Hitch up a trailer that weighs the full 3,500 kg, with 350 kg on the tow ball.
GVM. The vehicle has 800 kg of payload (3,100 − 2,300). The tow ball takes 350 kg of it. That leaves 450 kg for people, gear and accessories.
GCM. The trailer puts 3,150 kg on its own axles (3,500 − 350). If the vehicle is loaded right up to its 3,100 kg GVM, the rig weighs 3,100 + 3,150 = 6,250 kg. That is 250 kg over GCM.
To stay within GCM with the full trailer, the hitched vehicle can weigh at most 6,000 − 3,150 = 2,850 kg. Take away the empty vehicle (2,300 kg) and the tow ball (350 kg), and you have 200 kg left for everyone and everything in the vehicle.
Two adults and a fridge can use most of that. So in this illustration, the "3,500 kg" vehicle can tow 3,500 kg only if it carries almost nothing else. Nothing on the trailer's compliance plate or the vehicle's brochure is wrong. The limits just don't all fit at once.
What this means when you choose a trailer
- Start from GCM, not towing capacity. Work out what the vehicle will weigh loaded for a trip, then see how much GCM is left for the trailer.
- Check the tow ball rating against the trailer you're buying. As in limit 3 above, a heavy trailer brings a heavy download with it.
- Check the towbar and tow ball. Each has its own rating, from the list of limits above. The most common 50 mm tow balls are not rated beyond 3,500 kg.
- Leave a margin. RACQ reports that experienced caravanners suggest keeping the trailer to about 70% of the vehicle's maximum towing capacity. That is a suggestion, not a rule.
- Check your state's rules. Queensland, for example, lets you tow a trailer whose ATM is above the vehicle's towing capacity, as long as it isn't loaded beyond that capacity. Other states word their rules differently.
A GVM upgrade doesn't automatically raise GCM or towing capacity. Raising GVM without GCM reduces the trailer you can tow when fully loaded, and in WA, GCM can't be re-rated unless further technical requirements are met. If your vehicle has been upgraded, check exactly what the upgrade was approved for. See GVM upgrades.
Common questions
Can my 3,500 kg rated ute tow a 3,500 kg caravan?
Only if every other limit above also allows it: GCM, GVM, the tow ball rating, the rear axle, the towbar and the tyres. In many cases, as in the illustration, towing the full 3,500 kg leaves very little of the GCM for the vehicle's own load. Check the figures for your exact variant in the owner's manual.
Does the tow ball weight count towards my GVM?
Yes, as in limits 2 and 4 above. The tow ball load is carried by the vehicle, so it counts toward GVM and uses part of the rear axle's limit. That is why a heavy trailer reduces how much you can carry in the vehicle.
My caravan's ATM is higher than my towing capacity. Is that illegal?
It depends on your state and how the caravan is loaded. As above, Queensland allows it provided the caravan is not loaded beyond the vehicle's towing capacity. Check with your state road authority.
Can I increase my towing capacity?
Towing capacity and GCM are set by the vehicle manufacturer, and, as above, a GVM upgrade does not raise them on its own. In NSW, if you need to change a vehicle's towing capacity, seek advice from a licensed certifier. Other states have their own processes; GVM upgrades covers how they differ.
Sources
Authorities
- Safe Towing Guide — Department of Transport, Western Australia
- Caravans — Transport for NSW
- Towing vehicles and trailers — Queensland Government
- GVM and GCM FAQs — Department of Transport, Western Australia
Motoring associations (advice)