Why a 3500kg tow rating may not really be a 3500kg tow rating
Can tow 3500kg! The claim is there in big bold letters in the brochure, but here’s why your 3500kg tow rating may not really be a 3500kg tow rating.
Article updated 12/06/2015 with some clarifications based on comments by readers.
Part 2 now available – Everything you need to know about towing heavy trailers.
The short explanation is that most vehicles, particularly utes, can only tow their maximum braked trailer weight with a light load otherwise they exceed their design limits for weight. And that is the asterisk which usually sits behind those bold 3500kg claims.
The full explanation follows, and it starts with some definitions:
Tare (or kerb) weight – how much the vehicle weighs, stock standard. There is no exact definition of ‘stock’, as sometimes it means full of fuel, sometimes partially full, sometimes there’s an allowance for the driver, but it’s basically empty although ready to drive.
GVM (Gross Vehicle Mass) – or the maximum the vehicle can legally weigh. This is on the vehicle’s placard, and is a definite figure that is readily available for all vehicles. It is often the same for all types of given model, but might vary a bit with trim level, engine or body style.
Payload – the difference between the GVM and tare. For example, tare of 2000kg, GVM of 3000kg, payload = 1000kg. Payload is everything that is put on the truck or it has to carry. That includes bullbars, stronger tyres, roofracks, winches, canopies, storage systems, occupants, camping gear, recovery gear. Typically a modified touring 4WD has gear that weighs 200-400kg, and by the time a family of four has kitted up and is ready for touring you’re looking at 900-1000kg. I’ve done the maths a few times.
Front and rear axle load – how much weight can be placed on either axle. Usually the sum of the two axles is more than the GVM. For example, in the case of the Ranger it is 1480kg and 1850kg totalling 3330kg, 130kg more than the 3200kg GVM. This means there’s a bit of flexibility in exactly where the load is positioned over the axles. Beware of some aftermarket GVM upgrades which merely move the GVM to total the sum of the axle’s ratings, as then you lose that flexibility.
Braked tow rating – how heavy a trailer the vehicle can tow, provided it has trailer brakes as opposed to no brakes in which case it relies only on the towcar to stop the combination. Trailers over 2000kg need brakes that can be independently applied from the tow vehicle.
The braked tow rating is the trailer’s ATM, or Aggregate Trailer Mass. That’s how much the trailer weighs. The Gross Trailer Mass (GTM) is the ATM with the towball mass (downforce) subtracted. For example, a trailer that weighs 2000kg has a 2000kg ATM, and if there’s 200kg on the towball the ATM is 1800kg. The ATM is the trailer equivalent of the GVM. Trailers also have an unladen weight, the kerb weight.
GCM (Gross Combined Mass) – How heavy the combination of the vehicle and trailer can be. This should be, but isn’t always, the sum of the GVM and braked tow rating (maximum ATM of the trailer).
Now that’s out the way let’s look at some numbers, all in kilograms:
|Spec \ vehicle||Ford Ranger PX dualcab||Nissan Navara NP300 ST-X dualcab||Holden Colorado LTX dualcab||Isuzu D-Max LS-U dualcab||Mitsubishi Triton MQ Exceed dualcab||Isuzu MU-X LS-T||Mitsubishi Pajero 3.2 Exceed||Land Rover Discovery TDV6|
|Front axle load||1480||1320||–||–||1260||–||1330||1450|
|Difference: GVM, axle loads||130||110||–||–||200||–||80||95|
|Max braked tow||3500||3500||3500||3500||3100||3000||3000||3500|
|Max car weight at tow max||2500||2410||2500||2450||2785||2750||3030||3240|
|Loss of payload at tow max||700||500||600||500||115||0||0||0|
|Max trailer weight at car GVM||2800||3000||2900||3000||2985||3000||3000||3500|
|Loss of trailer load at GVM||700||500||600||500||115||0||0||0|
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An interesting set of figures. If we take the Ranger then that’s a 6000kg GCM, and let’s say we want to tow 3500kg. That means 6000 – 3500 = 2500kg, the maximum the Ranger can weigh if it is to tow 3500kg.
The Ranger’s tare weight is 2200kg, so 2500-2200 = 300kg of payload. Which is not very much at all, if we put four people in the truck they’d need to be 75kg each as 75kg * 4 = 300kg. Now you see what we mean when we say that the 3500kg tow ratings aren’t always realistic. And the Ranger’s kerb weight wouldn’t even include a towbar.
If we go the other way for the Ranger, looking at how much we can tow when at GVM then it’s this: GCM of 6000kg – GVM of 3200 = tow capacity of 2800kg, the most a trailer’s ATM can be.
Bottom line is if you work off the GCM then you can only tow 3500kg in a Ranger if you have no more than 300kg of load on the truck, or if the truck is at GVM, you can tow 2800kg.
However, there’s more to it. Remember those axle loads? Don’t want to exceed them, that’s for sure. A 3500kg trailer will need round about 300kg of towball mass and that needs to be taken into account too. I cannot do the maths here as I don’t know what the axle load is on a Ranger when empty (only its maximum), but let’s assume that the vehicle is at GVM and the front axle is weighted to the maximum. We know from the table above there’s 130kg left to play with, so let’s put all that on the rear axle. We know that 10% of trailer mass is the rough rule (and Ford recommend this too), so 130kg makes for around a 1300kg trailer. But in reality less, because a 130kg towball mass over a metre behind the rear axle produces a moment (leverage) so the net effect on the rear axle is greater (and the load on the front axle is reduced too).
Sound complicated? That’s because it is.
Now let’s now look at the new Nissan NP300 Navara. Here we have a GCM of 5910kg, subtract the 3500kg tow rating and we have 2410kg, the maximum the truck can now weigh. So 2410kg – 1910kg tare = 489kg of payload.
Or the other way around to determine what trailer we can pull at GVM: we have the GCM of 5910kg, subtract 2910 GVM = 3000kg towing. Then if we look at the axle load we see that there’s not a lot of play, with maximum combined axle load only 110kg more than the GVM. A 110kg towball mass translates to a trailer of around 1100kg.
Some people claim this calculation is double-counting. It’s not. A trailer that weighs 3500kg still needs to be controlled by a vehicle and whether the mass is on the trailer’s axles or the towball makes no difference, it’s all part of that 3500kg figure. But, the towball mass at the same time does create a significant downforce on the rear axle which is load on the towcar.
Some have said if the vehicle is at GVM you cannot tow. Remember there is usually some rear axle load left once the vehicle is at GVM. That can be used for towball mass provided the load is reduced to keep the vehicle below GVM.
The Pajero is another case again. Mitsubishi state that the maximum towball mass is 250kg: “maximum towball download (kg) when towed weight is 2,500kg or less” but above that (2500-3000kg) it is 180kg. They also say that “a weight distribution hitch is recommended for towball downloads exceeding 135kg.”.
These are just examples. If you look at the fine print of just about any vehicle – but especially utes – there’s all sorts of complications once you start approaching maximum tow capacity and it’s certainly not a case of hook up and hope.
It is also interesting that the wagons tend to have a GCM equal to their GVM and maximum tow rating, whereas the utes do not. Could this be because the utes have had their tow rating pushed a bit higher than what it should be? Also note that the Triton can “only” tow 3100kg, but it loses only 115kg of payload when at its maximum of 3100kg. It might not have the headline 3500kg, but realistically the numbers show it is real-world equal to the others.
The bottom line
Very few vehicles can tow their maximum rated tow weight when at their GVM, or even sometimes quite a way off it. The headline tow figure may not be usable in real life.
- If the sum of the GVM and max tow rating is greater than the GCM, then you have to choose between a fully loaded vehicle or the heaviest trailer it’ll tow. You have to take a close look at exactly what the manufacturer is saying about maximum towing capacities. This is unlikely to a simple answer – hence this long and jargon laden article – so you need to ensure that anyone you take advice from actually has a clue about your specific vehicle and trailer. Further tip – salespeople looking to close a deal are not known to be the most reliable source of technical advice on complex matters;
- Don’t assume a weight-distribution hitch (WDH) is the solution. Some manufacturers mandate a WDH, some recommend, and some say definitely do not use it;
- If a vehicle is set up for offroading with the usual accessories it will weigh 200-400kg over tare. This may reduce its towing ability as it may exceed its GCM once a heavy trailer is connected, or the driver gets in. In fact, some vehicles are so heavily loaded and modified they’re at GVM before anyone gets in;
- It doesn’t matter what sort of suspension or brakes you fit, if the compliance plate isn’t changed your GVM is what it is;
- Be aware of your weights as there are legal, insurance and warranty implications if they are exceeded;
- There are enough utes with broken chassis in the world already. Either take less load, or get a bigger ute like a F-Truck or a small truck like an Iveco Daily or a Mitsubishi Canter. Or if you really want a giant trailer, try a 5th-wheeler.
- Some vehicles are speed-limited when they tow. Holden recommend that Commdores be limited to 80km/h once the load is over 1600kg, or has less than 1500km on the clock. In general, 2WD roadcars are not as good at towing as 4WDs.
Tow car tips
- The unbraked tow weight often 750kg for 4X4s, but that’s a legal maximum. For smaller vehicles it can be much less;
- The braked tow weight can vary across models. The GU Patrol could tow 2500kg, 3200kg, or 3500kg depending on whether it was the 3.0 or 4.2, manual or auto. Weights of any type (GVM, tow, GCM) can be very specific to certain model, year, engine, driveline and trim level;
- TSC is trailer stability control. This is a variant of stability control that is designed especially to deal with trailer sway. One of those things you may only need once in your life but it kind of pays for itself right there and then. However, as with any electronic aid, consider it an aid, not a free pass to just add more weight;
- A good towcar will have a GCM that is the sum of its GVM and maximum braked tow rating. It will be all wheel drive, diesel, automatic, powerful and have TSC;
- The maximum tow rating can only be achieved if the towbar is rated appropriately. Not all towbars are so rated;
- Always go for a tow vehicle that is rated well in excess of your trailer’s weight, for example a 3000kg rated vehicle for a 2000kg trailer. It’ll do the job much more easily and safely. And you tend to avoid complications as described here;
- If you tow offroad, as in low-range territory, then reducing the trailer load by about 1/3 is a good idea, for example a 3500kg car would then tow a trailer with an ATM of no more than 1200kg;
- Modern automatics can be pretty much left in Drive when towing. The electronics are smart enough to use the correct gear out of the 6 to 8 they use, and will not overload the vehicle in any particular ratio; and
- Short wheelbase vehicles are not necessarily bad towcars. They have a very short distance between the rear axle and the towball which is good for trailer control. The Defender 90 is rated to 3500kg, same as the 130, and the shortie Prado when it was available had a higher rating than the long wheelbase version.
Towing figures are the new power figures. We used to obsess over kilowatts and torque, and to some extent we still do, but the manufacturers need another headline figure and now it’s tow ratings. The bigger the number the better, and even if you don’t tow an impressive rating gives an impression of capability, strength and power. So that’s why manufacturers are driven to go for higher and higher tow figures – it’s all marketing, and we can expect to see more of the same with the new utes coming onto the market.
When Ford shifted the Ranger from 3350kg to 3500kg shortly after it was launched I suspect that was mainly done to combat the Colorado’s 3500kg rating. Realistically, the amount you can tow in a Ranger rated at 3350kg is the same as one with 3500kg, such are the caveats around the higher figure.
Once you start pushing the limits of a vehicle like this then you run into limitations about exactly how that load can be towed, and that is how we’ve ended up needing to know all sorts of trailer tech jargon only to discover maybe you can’t actually tow that big trailer after all.
This article has been very popular, so we have written a follow-up. If there is a specific vehicle you’d like us to investigate comment below.
You may also like to calculate your caravan’s towball mass using the interactive Ball Weight Calculator.