Towing Guide

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Don’t let this happen to you

So you are looking to tow a large caravan or large boat and perhaps you’re a little confused as to what vehicle to buy, particularly if you are planning to tow more than 3000kg’s. You could be forgiven for thinking that most SUVs you see advertised on television are good to tow 3500kg’s and you would certainly think that the American pickup trucks you see advertised on television would easily do the job.

The purveyors of these trucks would have you believe their trucks could move mountains, even eat other utes for breakfast and tow 4.5 tons. Well let me tell you, you should be concerned as their misleading advertising could lead you down the path of heavy on the spot fines. In Western Australia you can receive up to a $2500.00 fine for being over loaded, the size of the fine is dependent on how overloaded you are.

The main area of concern is the vehicles payload capacity, that being the total weight you can place in or on the tow vehicle without exceeding the vehicle GVM, (Gross Vehicle Mass).

According to Government Authorities, most of checked vehicles towing medium to large caravans and boats fail the GVM test on the side of the road which can result in these heavy fines.

1. Things to Know
2. Are You in the Clear?
3. Some Examples
1. Things to Know

There are four weights to consider when choosing your tow vehicle, GCM (Gross Combination Mass) this weight is set by the vehicle manufacturer, it represents the total combined weight of vehicle including caravan/boat, people, fuel, gear and vehicle accessories. This weight is locked in concrete and cannot be increased and I would suggest, if someone says they can increase your GCM, that you contact your state licensing technical centre before you go down that path as there are only one or two vehicles on the market that got federal approval to increase the vehicle GCM by using a loosely worded ADR before that gate was shut. There are certain circumstances where GCM can be increased by a SSM (Second Stage Manufacturer), but this is a very grey area and licensing authorities may try and discourage you from going down that path as the vehicle would be operating outside the vehicle manufactures design envelope.

Next up is the vehicle GVM (Gross Vehicle Mass), the maximum all up weight your vehicle can weigh including people, fuel, accessories, gear and the big one, ball weight, that being the weight placed on the tow ball from your caravan/boat, which should be approximately 10% of the weight of whatever you are towing. GVM can be increased by an approved engineer, however it is limited by the maximum axle load rating for front and rear axles. This increase can in most cases be limited to just 100 -300kg and this can result in an equivalent  loss of towing capacity because you can’t exceed your GCM.

Tare or curb weight is the weight of the vehicle as it comes off the production line.

Finally, the vehicle towing capacity as set by the vehicle manufacturer and this is where it all starts to get really confusing, where vehicle manufacturers walk a fine line between the truth and misleading advertising.

2. Are You in the Clear?

When it comes to making sure you are currently legal, there is an easy way for you to very accurately check. Firstly, make sure you find out the actual GVM and GCM of your current tow vehicle. There is no point cheating on the next bit. You load your vehicle up with everything that you take with you including a full tank of fuel and water if you are inclined to fill your water tanks. I say this because the heavy haulage boys are notorious for setting up on the outskirts of a large country centre where they will find you at your heaviest and they won’t let you drain your water tanks to lighten your load either, because they know you are going to fill them up at your first opportunity.

Next take your vehicle to the nearest public weigh bridge with mum and the kids and the dog on board, drive onto the scales stopping short of allowing the trailer wheels from entering the weighing area, this will allow you to check your vehicles loaded weight including the ball weight of you caravan or trailer. You might be shocked to learn that 92% fail the GVM test. Now you drive your entire rig onto the scales to check your GCM. If either of the two weights are over, you are running the risk of receiving these nasty on the spot fines and it’s also a get out of jail card for your insurance company should you be unfortunate enough to be involved in a motor vehicle accident. Worst still, if it was found that your overloading vehicle was the course of an accident involving a fatality, one would hate to think what would happen then.

With many holiday makers investing in excess of $200,000 in their tow vehicle and caravan, you have a duty of care to make sure you are legal at all times, if you think you might be overweight, go through the exercise. I meet people every day that tell me that they think they are on the limit, but don’t want check in case they are overweight, they just stick their head in the sand and don’t want to talk about it. If your vehicle is overloaded, get a smaller caravan or boat, or get a bigger tow vehicle and make sure it can legally do what you want it to, don’t take the salesman’s word, you check the numbers yourself, because there’s half a chance the salesman you are talking to is clueless.

3. Some Examples

Let me give you some examples, I use a very simple calculator to work out how much payload a vehicle has available, but first you must find out the vehicles GCM, Towing capacity and Tare weight. The calculation is simple, GCM, less Towing Capacity, less Tare weight, what remains is available payload capacity. There are a lot of utes and wagons sold in Australia that they promote as being about to tow 3.5 tons. Let’s take Mazda BT 50, a popular choice for towing a decent size caravan, it has a GCM of 6000kg, less 3.5ton towing capacity = 2500kg, less tare of 2250kg = 250kgs, not a lot when you consider that you have to take fuel, people, canopy, dual batteries, fridge, bull bar and personal effects out of the  250kgs, it doesn’t go very far especially if, like many of you have, fitted a LR fuel tank. 

A lot of American pickup trucks fall victim to this problem, in fact some of them can be much worse, but before I single out any of these vehicles, let me clarify the nomenclature of the model designation, for example a RAM 1500, we could be forgiven for thinking that the 1500 is a reference to payload capacity in kilograms, but in fact, it is a rough guide to payload in pounds, I say rough guide because a new Ford F150 has a very different set of numbers because of its lightweight aluminium construction and higher GCM. 

Here are two examples,

Using the RAM 1500 catalogue as my source of information and using my simple formula, some scary numbers emerge. The RAM 1500 Laramie with a 3.92 Axle ratio has a GCM of 7237kgs less 4500kg towing capacity = 2737kg, less kerb weight of 2650kg = 87kg of payload and according to the brochure, occupants, fuel and fitted accessories, the weight of which, must be deducted from the payload to determine the load carrying capacity. This is concerning to say the least and reinforces the need to do your homework. 

Let me give you another example that can lead you down the path to overloading your vehicle. Many of you will have looked at, considered or even purchased one the new HSV Silverado 2500 HD LTZ that you can drive on a car license, this is classified as an NB1 category vehicle. The fact that you can drive one of these vehicles on a car license is of a concern when it comes to payload capacity. Take the Silverado 2500LTZ for example, it arrives into Australia with a factory GVM of over 4500kg, an NB2 category vehicle, which you would need a Light Rigid (LR) license to drive, a very simple license to obtain and doesn’t even require a written test. These vehicles would have been de-rated so that their GVM is under 4500kg. This is a common practise on the East Coast of Australia as it not only saves you a lot of money in stamp duty, it also negates the need to get your LR license. However it also results in a lower payload of just 875kg, that’s less than a Mitsubishi Triton ute. Out of that 875kg, we have to deduct the ball weight of say, 400kg, a full tank of fuel, bull bar, people, gear etc, and it’s not long before you are overloaded.

When considering the purchase of one these vehicles you must do your homework. One tip I can give you, find out what license you need to legally drive the vehicle. If the answer is a regular car license, proceed with caution. Get your hands on the specifications of vehicle you are interested in and use the simple calculation I mentioned earlier in this article. You should also do the same exercise in a vehicle that requires an LR license to drive, because quite often a GVM upgrade is required to meet your individual needs.