We as Australians, and explorers in general, love to tow. Whether it’s a camper trailer, a caravan, a purpose-built moto-carrier or a big old boat for those beach launches and sneaky runs out to those carefully marked waypoints, chances are if you own a fourby you probably either have a trailer or two, or are planning on getting (at least) one.
But towing, particularly off-road, isn’t without its drawbacks. It can mess with your steering, it can throw your weight distribution way off, it comes with its own set of handling rules and can generally set the fox among the chickens. However, with a little know-how, most of that can be avoided with the correct suspension set-up – and anything that can’t be fixed with suspension can be avoided with a little common sense. Let’s jump in and see what you need to know before you next hitch up.
START WITH GVM AND GCM... SERIOUSLY
We’ve all heard the “he was over GVM when he crashed and his insurance just laughed at him” horror stories, as well as the “he was just cruising along the dirt road when he hit that washout and his chassis just folded up” cautionary tales.
And yeah, while we’re not trying to tell you how to suck eggs, we will say that almost every single such misfortune could have been avoided if more attention was paid to GVM and GCM. Gross Vehicle Mass is the maximum weight your vehicle can legally be. Gross Combined Mass is the maximum legal weight your vehicle and trailer can be. Go over either figure and kiss your insurance, safety and vehicle reliability goodbye.
Seriously, get your 4x4 and trailer packed up and take it over a weighbridge then bring the weights down accordingly if you need to. Keep in mind also that every single vehicle manufacturer bar Land Rover do NOT have an off-road towing capacity, and Land Rover’s drops to less than half when on the dirt, so slowing down and driving to the conditions as well as your vehicle’s strengths and weaknesses will do way more than any suspension set-up can.
But this is a suspension article, so let’s get to it.
THE CONUNDRUM: LOADED VS UNLOADED WEIGHTS
Here’s the thing: when you’re towing heavy, you need a higher spring rate (stiffer springs, essentially) to support the ball weight of the trailer and mitigate the swaying effect a trailer can produce. No big deal for a dedicated tow rig, but what about those of us who also regularly drive around unladen? Not many people are willing to put up with a ridiculously stiff rear end just so when they’re doing the run to the boat ramp on the weekend their ride will be acceptable. Then there’s the amount of ball weight you’re expecting to have. A box trailer with a couple of dirt bikes and a few bits of camping gear won’t need the same upgrade as a 25ft caravan. When it comes to dialling it in to suit your needs, you have a fair few options ranging in price, convenience and ease of use.
HEAVY DUTY SPRINGS
These are a good idea if you’re a tradie who carts a lot of tools around during the week and then chucks the camper trailer on the hitch Friday after knock-off. However, unless you’re constantly hauling heavy weights, they can significantly upset the ride and handling of a vehicle that’s empty. Progressive springs (fun fact: all leaf springs found on dual cab utes, other than the Navara, are by their very design progressive) can mitigate this somewhat, but you’ll still sag an inch or two before the higher rate on the spring kicks in which is not exactly ideal.
"HD Springs are good for some, but most won’t like them full-time."
PNEUMATIC HELPER SPRINGS
Ah, airbag helper springs. Probably the most used and abused suspension mod this side of slipping the front bolt out of a radius arm and pretending like you actually have flex. A cursory scan of just about any internet discussion will have you come across plenty of statements about how they bend chassis’ and are the worst thing since sliced cancer. It’s all absolute BS of course – airbags don’t bend frames; overloading, exceeding GVM and driving too fast over washouts and corrugations do. Sure, under such circumstances they will provided a stress locating point on your frame, but when used within their design parameters they’re actually one of the handiest towing aides out there.
The trick here is to keep an eye on your ball weight and bag inflation pressure. It’s easy to throw a few too many psi in there and you’re headed for trouble. If you’re towing heavier than the bags can handle, it’s time to look into other options.
"No, they aren’t the Devil. In fact, probably the best option for most people."
FULL AIRBAG REPLACEMENT SPRINGS
These are rare. Mainly because they’re not easily installed on a leaf-spring rear end (nothing is impossible though), meaning they’re best suited to coil rear ends – of which there are limited options. With that said, full replacement bags offer the best in having an almost infinitely tuneable spring rate without ever having to sacrifice suspension travel. Don’t underestimate how awesome that is either.
Hitching up the van? Flick the compressor switch and let the bags lever it out for you. Heading down the beach with the kids and a surfboard, let your fourby make cool ‘pssssssht’ noises as you bring the back end back down to deal with your lack of weight.
They’re reliable too. The trucking industry has been using airbags for decades now with excellent results in terms of durability; if you’ve got a towing 200 Series (for example), you could probably do a lot worse.
"They won’t suit every vehicle but will make life way easier."
A COUPLE OF QUICK TOWING TIPS
Not suspension related, but will make towing a whole lot nicer.
Drop your trailer tyre pressures at the same time you drop your vehicle’s
Distribute the heavier items in your trailer as low as you can and as close to the axle(s) as possible (directly above is ideal)
Too much ball weight will have an affect on your vehicle’s caster. Which can bugger your steering geometry. Which is dangerous… you can see where we’re going here, right?
The less weight you can carry the better. Trust us, you really don’t need that spare gearbox or that solid oak coffee table when you’re in the bush. Yes, I know it’s a conversation starter but stop it
Slow down. The forces acting on your suspension, and tow vehicle in general, are magnified when off-road. Arriving to camp half-an-hour later than your buddy (whom you privately think is a bit of a knob anyway) won’t hurt, and you’ll get to see heaps more along the way too