Must have vehicle modifications for towing

In this ultimate guide to towing series, Robert Pepper discusses preparing your vehicle for towing, including modifications that are mandated by law, others that are highly recommended, and some that are just nice to have.

Few vehicles are ready to tow heavy trailers straight from the showroom floor, and the heavier the tow, the more you’ll need to modify. Here’s a list:

Towbar & hitch

What it is

Where you attach the trailer to a vehicle! You’ll need a hitch and at least one tongue, as shown below.

Why you’d want it

It’s hard to tow without one.

Options

Your vehicle may come with a towbar. If it doesn’t, and is rated to tow, then you have the choice of an OEM (Original Equipment Manufacturer) version or aftermarket.

Cost

$0 if included to $2000+.

Advice

Make sure the towbar is rated to the maximum tow capacity of the vehicle. For example, don’t fit a 3,000kg rated bar to a car capable of 3,500kg unless you’re sure you will only tow 3,000kg, as the lowest limit applies.

The OEM towbars come with full manufacturer’s warranty. The aftermarket towbars do not, but you get a wider choice of bars. For example, OEM bars are not typically focused on offroad driving, whereas aftermarket bars may incorporate recovery points, or be raised for a better departure angle. These bars may require a drop hitch to lower the towball to the appropriate height.

If you have a towbar fitted, also ensure towing electrics are fitted too. Typically a 12-pin flat plug is the most flexible. You may also find it cost-effective to have an electric brake controller fitted at the same time and an Anderson plug (see end of article).

If your car does not have a tow rating from the manufacturer, then you should consult an automotive engineer licensed by your state for advice before you attempt any towing.

Electric brake controller

What it is

A means to control the trailer’s electrically operated brakes. There are two basic modes; towcar synch, so when the towcar brakes the trailer brakes are applied, and independent, which is when the trailer brakes can be applied independently.

Why you’d want it

Electric brake controllers and electrically operated brakes are far superior to overrun brakes, which activate only when the towcar slows the trailer. In other words, ‘runs into’ the back of the towcar.

This is because the sensitivity of electric brakes relative to the towcar brakes can be varied by the driver according to the conditions, and the electric brakes can be operated independently of the towcar brakes which is the single best way to combat trailer sway – more on that later.

Options

A few vehicles have built-in controllers, notably the next-gen Ranger and Everest, and some of the big American utes.  For everything else, it’s aftermarket. There are several brands, such as the well-known REDARC, Tekonsha and Hayman Reese. All these require installation in the towcar, but there’s an easy non-install option; the wireless Elecbrakes system, which doesn’t need any modification to the towcar at all.

Cost

Expect to pay around $400-$800 installed, depending on the controller and complexity of the job.

Advice

Trailers over 2,000kg GTM require independent brakes, and they are a good idea for trailers below that mass for safety’s sake, especially if you tow offroad.  If you do a lot of towing, a permanently installed controller is a good idea. For one-offs or temporary use consider Elecbrakes, although that too can be used as a permanent braking system.

Whichever system you use, ensure you know how to adjust its sensitivity and operate it independently. No brake controller is simply install and forget if you want to be safe on the roads, and the owner’s manuals typically do a poor job of explaining the concepts involved in safe trailer braking.

Towing Mirrors

What it is

If your caravan is wider than the towcar, you’ll need mirrors wider than the caravan.

Why you’d want it

For safety and legality.

Options

Two basic types; clip-on and replacement. Fully explained here.

Cost

$150 for clip-ons to $1500 for replacements.

Advice

The replacement mirrors are superior because they’re less hassle to set up, have better visibility, less bouncing, can’t be stolen, and won’t be knocked off by an errant bush. Their sole con is that they’re more expensive.

Suspension

What it is

Uprated suspension more suitable for heavy-duty towing. Suspension is comprised of two basic parts; a spring, which sets the ride height and carries the load, and a shock absorber (damper), which damps out the bouncing.  Springs may be coils, leaves or, rarely, torsion bars.

Why you’d want it

The standard suspension on any vehicle is very much a compromise between a comfortable ride around the ‘burbs with no load, and carrying the maximum payload plus towing heavy.  As a result, most suspensions aren’t optimised for heavy towing, and the car’s back end sags even under moderate towball masses.  This leads to poor handling, impaired braking and steering, and potentially greater tyre wear. 

So, for any heavy towing – loosely defined as more than half the max braked capacity – consider a suspension upgrade, which could be a complete replacement, airbags, or just stiffer rear springs.  Without it, you may not be able to safely tow anywhere near max capacity. The problem is that every 1 kilogram of TBM translates to about 1.5kg on the rear axle, and 0.5kg off the front axle, so a 200kg TBM may mean around 300kg extra on the rear axle…which is a lot.

Options

There are three basic options:

• Stiffer rear springs
• Airbags
• Complete replacement

The usual problem with the stock suspension is the rear sagging. This can nominally be fixed by rear springs, which are either taller, so “sag” is the same but ends up with a higher ride height, or springs the same height but stiffer. Or both. The problem is then that the springs are not matched to the shocks, and the suspension characteristics on the rear may not be matched to the front.

Airbags are not the safety devices in this case but inflatable bags that take some of the strain off the rear springs. The advantage is they can be largely deflated when not towing, restoring the original suspension characteristics, whereas stiffer or taller rear springs may lead to a harsher ride when unloaded. However, they only help support the load and reduce sag, not increase ride height.

A complete replacement suspension means four new springs and shocks, all matched, usually with a lift of around 2”, which helps with offroad performance.  This should also provide a stiffer or taller rear spring that is better able to cope with heavy towing loads.

Cost

Stiffer rear springs may cost you around $500 fitted, all the way up to $5000 for a full suspension replacement.  Selling the old parts is usually worthless.

Advice

If all you want is the rear end to stop sagging then stiffer rear springs will do the job, as may airbags. The ideal solution is a complete suspension replacement and that is recommended if you intend to drive offroad. But even with a replacement, airbags may help so they will never be a bad investment.

GVM Upgrade

What it is

An increase in the GVM (the maximum the vehicle can weigh) carried out to increase the payload.

Why you’d want it

Increase carrying capacity of your vehicle, and maybe also effective towing capacity. A GVM upgrade won’t increase your braked tow from say 2,500kg to 3,000kg, but if you were limited by GVM trying to tow a 2,300kg trailer, the GVM upgrade may allow you to get back to 2,500kg. Towing weights are complex!

Options

Many different companies offer GVM upgrades. If you are looking at a suspension upgrade, consider a GVM upgrade as part of the package. It’s nice to have the reserve capacity even if it’s not used.

Cost

Very variable depending on the vehicle, but ballpark around $3000-$7000.

Advice

A GVM upgrade does not increase the braked tow capacity of your towcar, and in most cases, nor does it increase the GCM.  You may therefore, find that you can tow less if you use the extra payload in your GVM upgrade. Example; GVM 3,000kg, GCM 6,000kg, braked tow 3,000kg.  Increase GVM to 4,000kg, but GCM remains the same, so 6,000kg – 4,000kg = 2,000kg; that’s your new max tow as you’re now GCM-limited. However, if the limit you were running into was GVM, then you may be able to tow more.

There are two basic types of GVM upgrades; axle-sum and axle re-rate.  The former simply sums the front and rear axle loads to make a new GVM. Example; front axle 1,600kg, rear axle 1,800kg, GVM 3,000kg. New GVM is made 3,400kg which is 1,600kg + 1,800kg.  These are a trap if your rear axle is the limit.

An axle-re-rate GVM upgrade re-rates, but does not upgrade the axles. Example; front axle 1,600kg, rear axle 1,800kg, GVM 3,000kg. New axle limits of 1,700kg and 2,000kg, new GVM 3,600kg allowing for 100kg under the axle sum, which is a good idea for front/rear load flexibility. A GVM upgrade done prior to registration is valid anywhere in Australia (pre-rego), one done after rego is valid only in that state (post-rego).

Bear in mind that the carmaker has designed the car to operate not beyond its GVM, or GCM. If you do select a GVM upgrade, then expect increased maintenance and running costs as parts wear out much quicker.

Long-range fuel tank

What it is

An extra fuel tank in addition to the existing tank, or a larger replacement tank.

Why you’d want it

Towing increases fuel consumption and, therefore, reduces range.  A bigger fuel tank restores or even increases range and is a much safer and more convenient option than jerrycans. You also don’t lose any storage space.

Options

Not all vehicles can be fitted with a long-range tank. Sometimes, there’s no space, and other times, there’s insufficient demand to make production worthwhile. The two basic types are auxiliary, which is a separate tank that uses a pump to transfer fuel to the main tank, and replacement, which entirely replaces the original tank with a larger unit.  Typical increases may be 40 to 100 additional litres of fuel.

Cost

Approximately $1500-$3000 fitted.

Advice

Not essential, but once you have one you won’t want to go back.  Will make resale easier too.  If you drive offroad, ensure that rampover angle is not reduced. Some tanks only fit specific models, so check the exact model of the car you intend to buy, don’t assume based on a generalisation.

Vehicle-specific problem-fix upgrades

Some vehicles have specific towing weaknesses. For example, I run a larger radiator in my Ranger as it was not designed to pull 2,500kg over sand dunes for hours. 

Remember, the maximum braked tow capacity is the manufacturer’s maximum, and they didn’t plan on it being a continuous load. Research your specific vehicle and see what, if any, problem-fix modifications there are for towing.

However, beware of OldMate58 back-in-the-day advice; an old automatic gearbox with three speeds plus overdrive is a very different beast to the modern 8-10 speeder with far less need for cooling or torque convertor lockup kits.

Accessories

These are items that don’t change your vehicle, but you may carry and find useful:

Driving lights & additional lighting – nobody ever said “that’s too much light from my headlights”, so adding driving lights may well be helpful. These days LEDs are the technology to get. You may also consider sidelights to help when hooking up or manoeuvring.

Trailer camera – very useful so you can see where you’re going backwards!

Car storage – particularly for utes, you’ll need to tie a few things down

Anderson plug – provides electrical power from car to caravan to charge the caravan’s batteries.

Air compressor – adds air pressure to tyres, handy if you go offroad or even on longer dirt roads, and you can get by putting air into a slow-leaking tyre.

Plug tyre repair kit – if you get a puncture, you may be able to quickly and easily plug it as opposed to swap on the spare and then you’re going to be immobilised by the next puncture.

What you don’t need

A lot of towing vehicles are modified 4x4s with a lot of gear that is offroad-specific such as taller, light-truck construction tyres, snorkels, winches and the like. This is a towing guide, not an offroad guide, so we’re not covering those offroad-specific modifications.  For example, you don’t need to swap out your tyres unless you’re planning on offroad work.