Setting up your 4WD to tow safely
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Get the expert Secrets! GVM vs. GCM – Towing weights explained
If you tow, or are planning to tow, then this is a great article for you. There is a lot if important information you need to consider when setting up your tow vehicle before you hitch the trailer to keep yourself both safe and legally compliant. When you are planning to add 2.5 tonne to 3 tonne behind your 4WD your are driving a completely different vehicle. Weight changes the suspension and steering geometry, wheel alignment, engine capability plus, you're now twice as heavy and trying to stop with same brakes and rotors. Towing heaver loads is no joke and this article gives you the top 5 things you need to consider if you are getting ready to add serious weight behind your 4x4. This article covers our Top 5 mods that you need to understand, and in what order, for safer towing.
1. Know your weight!
Towing weight is the single most important factor when towing. From the weight of your trailer, your vehicle, your tow ball weight, your GVM, axle loads, tyres all come into play and you need to know these to set up your vehicle correctly. The 4 basic terms you need to understand and the data point they represent are:
GVM - Gross Vehicle Mass
This is the maximum legal weight your vehicle is allowed to be on the road. The GVM can be located on your vehicles build plate. This is the total weight of your vehicle without a trailer attached.
GCM - Gross Combined Mass
This is the maximum combined weight of the vehicle and trailer you are towing is allowed to be.
ATM - Aggregate Trailer Mass
Maximum weight of your trailer, this is like GVM but for your trailer only. It is the maximum weight the trailer can be on its own as specified by the manufacturer.
This is the download weight your trailer applies to the vehicle's towball. This is important as it affects the vehicles payload.
This is the amount of weight your vehicle can carry without exceeding the GVM. And remember, this includes all of your accessoiries, fuel, food, passengers and tools or parts you are carrying. It also includes the towball weight of the trailer you are towing.
It is really important to understand these numbers and terms especially in relation to your own tow vehicle. If you exceed any of these numbers you are driving around illegally which will likely result in voided insurance in the event of an accident and could see you be held liable for negligence as well. Exceeding these weights also puts excess strain on your vehicles driveline, suspension, body and chassis which can also affect your vehicles warranty.
In this video we have listed a bunch of standard accessories and their typical weights to give you a better understanding of just how easy it can be to exceed your legal weight. Even just adding you core accessories for your next adventure could see you over your legal weight so make sure you take the time to understand these numbers and how they relate to your vehicle before heading out. And remember, you must include your towball weight in your calculations if you are towing (3:30 into this video) which makes reaching or exceeding your GVM even easier so be careful. Use a public weighbridge with all of your gear loaded so you can see the real weight of what you are travelling around with. Weight the vehicle on its own, then your trailer on its won, then both together. This will give you your vehicles weight and trailers weight relative to their GVM (Gross Vehicle Mass) and ATM (Aggregate Trailer Mass) and together will give you your GCM (Gross Combined Mass). When you are over your vehicle manufacturers recommendation it is time to start deciding what accessories or items you can remove from your set up as towing illegally is just not worth the risk.
Now you have your vehicle weights understood and likely left understanding it is heavier than you first thought, it is time to look at your suspension set up. There are a heap of suspension options out there to make towing heavy loads safer and, more importantly, legal. If you are planning on towing with your 4x4 it is almost certain that you are going to need to update your factory suspension. Factory suspension is not equipped to tow big loads and as we discussed when talking vehicle weights, can make it very unsafe to drive and handle poorly. Loading up heavy tow loads on factory suspension can lead to less responsive steering and poorer front braking performance as there is less weight over the front axle as the rear sits lower under load. Fitting your vehicle with the correctly rated suspension to suit the load that is being towed by your vehicle will allow for the weight to better distributed and reducing the impact on your steering and braking performance. Having the correct suspension for your towing needs makes your vehicle much safer, brake better and handle like factory however you are trading off the smooth suspension feel when you are not towing. Watch the above video for some great examples of the benefits of this and what a difference properly rated springs and suspension can make.
Another option that you may have, depending on your vehicle, is a GVM upgrade when you are upgrading your suspension. There are a number of GVM upgrades available for your needs or budget and can get basic affordable GVM upgrades like the one shown in this video (07:18) that include heavier duty springs and larger shocks to suit right through to larger kits that include bracing on the chassis and diff housing, brake upgrades and suspension upgrades. Each kit will have a different certified load rating that it increases your GVM as well.
Another way to greatly assist your load levelling is to fit what is called a load distribution hitch. These attach to your tow bar and use high strength torsional steel bars to help level your tow vehicle and your van when towing by decreasing axle load on the rear and distributing it to the front of the vehicle therefore levelling the vehicle out. They do not decrease the tow ball download imposed by your van on the vehicle, that remains the same all they do is distribute the weight better across the vehicle therefore making it more level and safer. A weight distribution hitch should not be used as a substitute for overloaded vehicles towing a heavy van as they will just mask the problem. Always make sure you have the right suspension set up for load and don't take short cuts with your safety just to save a few bucks. Get it done right the first time around and make your off-road adventures safer and certainly more comfortable.
The next thing you need to address of course is your brakes. Your factory brakes are really only designed to pull the vehicle up in a standard sort of form, add a couple of tons of caravan on the back and there's no way those brakes will work effectively. Adding a Redarc Tow Pro allows my 200 series to pull up about 10.8m sooner with my electric brakes operating compared to no brake controller. This was with me only travelling at 40 klm/hr with an already installed brake upgrade kit, that is a huge difference! Installing an electric brake controller will also reduce the rear load on the back of your 4x4 under heavy braking giving you a much more stable braking feel and limiting the chance of jack-knifing or becoming unhinged under braking load. If you are towing over 2 tons you are legally required to have an electronic brake controller installed.
My choice is the Redarc Tow Pro Elite that I use on all of my vehicles. This unit is very easy easy to control and installs nice and neat with only the control knob visible to control and adjust your braking. It also has two easy modes for your setup, proportional and user controlled braking. The proportional setting activates the trailer brakes in proportion to your vehicles braking level which is perfect for around town or on the highway as the unit will do all of the work for you. The user controlled braking setting you can manually dial in how much braking you want applied to the trailer with the in-cabin adjustment know which is great for steep descents and takes the load off the vehicle to manage the braking load.
As well as adding an electronic brake control unit you should also consider upgrading the braking components of your vehicle as well. A simple upgrade from your factory pads, rotors and brake lines to braided lines can be an easy way to pull your rig up faster and with options available for most makes & models it is an easy D.I.Y job.
4. Wheels & Tyres
Another thing that's often overlooked but is essential for towing big loads of course is your wheels and tyres. Commonly we'll just choose wheels based on looks and tires based on off-road performance but if you're planning to carry some weight you also need to factor in the load rating of your wheels and tires so they can handle the extra weight as well. So when it comes to choosing a set of wheels for your pride and joy don't just choose something that is aesthetically pleasing that looks good. You want to choose something that has a high load rating, now typically with a big GVM on a vehicle like my 200 series you're looking for a load rating of around 1500 kilos per wheel. The same goes for the tyres I choose, I went for a Goodyear Wrangler Duratrac because I got a maximum load rating of 1750 kilos, times that by 4 and you've got 7,000 kilos which allows for a full load, a heavy trailer in tow, and some room for when extra load is applied to the tyres like hitting a washout. Now when I was accessorising my 200 series series I had towing in mind. I really wanted to make this the ultimate tow vehicle, that's why with the Goodyear Duratrac I find they're a perfect all-rounder and I didn't want a big mud tyre on this vehicle because I probably wasn't going to use it in that sort of terrain. I find the Duratrac have an aggressive sidewall so if I do find myself off-roading a bit of mud or in a big rut I've got enough traction to get out but, on the road especially when I'm towing either a caravan or a boat I find this as a good combination the best of both worlds. They work off-road but they're also really well mounted on-road as well and perfect for towing.
Here's how to check the load rating of your tyre. On the side you'll have a number like this followed by a letter for the speed rating. In this example, these tires have a rating of 'Q' which means they're right up to 160klm/h.
Another tip to help you is to get the right tyre pressures when you're towing now on the highway. I typically run about 40 in the front and 45 in the rear, keeping in mind my 200 is a very heavy vehicle. When I hit the sand on a soft beach I'm straight away down to at least 18 psi until those tyres are really bagged out and on a dirt road the compromise is probably about 26 to 28psi. You just want to cut a little bit of air out of those tyres so they bag out a little bit and your ride is much more enjoyable. It's also better for the tyre if you head off road so make sure you air the tyres down on your vehicle, and your trailer, particularly on the beach like Fraser Island. This will allow the trailer to follow your vehicle's wheel tracks and stay on top of soft surfaces instead of digging in. When you stop it'll also create less of a hump in the front of the tyre which means it requires less effort to take off. You always want to coast to a stop on soft sand instead of slamming your brakes on so you don't dig a hole.
5. Vision & Communication: Towing Mirrors, Reverse Cameras and UHF's
Next up you've got to be able to see what you're actually towing. In fact if you're towing a really big van it can even be a legal requirement to fit aftermarket mirrors to your tow vehicle. The first are bolt-on tow mirrors. They may serve a purpose for your occasional trips but can move around a lot and some can even damage your door or your mirror if they come loose and rub. The other benefit is they give you much more vision around your canopy when you're not towing. The best solution has to be to fit a set of aftermarket mirrors like the ones on my 200 series from Clearview. They're not exactly a budget option however what's so good about them is you can see exactly what your towing which makes for a much safer experience on the road. Now when you're driving around town of course they stick in nice and flush to the vehicle, you put a van on the back you can just pull these straight extend these out out. This and it gives you so much more vision while keeping a relatively factory look to your vehicle.
Another worthwhile addition to your vehicle, if your vehicle doesn't come standard with one, is a reverse camera. Obviously a reverse camera makes it very helpful when you're trying to reverse up and attach a trailer, but it's also a really cool safety feature, especially if you've got kids or dog who might be running around while you're trying to reverse. A reverse camera is a must-have for your vehicle especially if you are towing frequently and there are aheap of great options to suit yuour 4x4 and van set up. Something else that is super important for just about every single four-wheel driver out there, but more important for people who do a fair bit of towing is good quality communications. Now of course I'm talking about a good quality UHF like the GME XRS connect that I use in the 200 series.
It is a great little unit to keep in your four-wheel drive and it's an in-cab 5 watt unit. I've matched this up to a 6.6 db aerial which I reckon is the best of both worlds. So if you're doing a fair bit of mountainous work as well as the big open roads you're going to find in the outback 6.6 will cover you for just about everything. Obviously a UHF is super important for keeping in communications with the rest of your convoy but I also see it as a bit of a safety feature. When you're out in the outback you're coming up to a road train or you know road conditions might not be that good you can warn other travellers and they can warn you. Keeping good communication is going to be the best safety device you have, especially when you're out on the open road. This is particularly important when you are on a dusty road and you're towing and you come up to a road train. Because you're towing it's going to take a lot longer to overtake which increases the risk. With the UHF installed you can simply send a transmission to the truckee and he can tell you if the road is clear ahead and wash off a bit of speed to let you pass safely.
Well there you have it, hopefully you've got to stack out of this article and particularly how to set your 4x4 up to be the ultimate tow vehicle. Now in my opinion it doesn't matter what make or model vehicle that you've got. Every single four-wheel drive out there can benefit hugely from a couple of key after-market accessories. Now that you understand the top 5 things you need to consider as the absolute essentials if you're planning on doing a lap around Australia towing a big caravan, a boat or camper trailer, or anything with a fair bit of weight behind you will make it a much safer and comfortable journey.