Driving with Trailer

Written by Norm Kerr

TIPS FOR TOWING

THE TOWING VEHICLE

Most modern passenger vehicles are designed to carry four or five passengers and a reasonable amount of gear not to tow a large home on wheels.

Ideally, the towing vehicle should be:

  •   Fairly heavy in relation to the item being towed. The regulations on mass ratio vary from state to state so do your homework.
  •   Capable of producing powerful torque (twisting power) at low engine speeds. Important in the stop – start conditions of heavy traffic as well as hill terrain.
  •   Robust construction and carry capacity, especially regarding suspension, tyres and brakes.

The towing capacity of most passenger vehicles varies widely so no “Rule of thumb” can be applied. It is essential that you consult the vehicle owner’s manual prior to using the vehicle for towing.

Most vehicle manufacturers have a towing package designed for their vehicles and when possible should be utilised. There are a lot of aftermarket products as well so once again do your homework and get it right the first time.

THE ELECTRICAL SYSTEM

The electrical system on most modern vehicles is quite adequate to carry the extra electrical load imposed by the towed trailer.

An auto-electrician should be consulted in respect of the following:

  •   The wiring of the trailer plugs/sockets.
  •   Battery storage capacity for “off the grid use”.
  •   Flasher unit rating and indicator tell – tail.
  •   The capacity of the alternator.
  •   The connection of internal appliances.
  •   The connection of electric braking systems.

THE SUSPENSION SYSTEM

Due to the mass imposed on the towbar by the nose of the caravan, some modifications (mods) to the rear suspension may be necessary. The mods may include:

  •   Heavy duty rear springs.
  •   Additional rear springs.
  •   “high lift” shock absorbers.
  •   And/or air adjustable shock absorbers (to name just a few).

The aim of modifications is to restore the rear of the vehicle (when laden) to its original unladed height. This brings the vehicle back to its normal operating position. Care must be exercised to ensure that the rear axle is not overloaded.

TYRES

Tyres of the highest load carrying capacity approved by the vehicle manufacturer should be fitted where extensive towing is anticipated. Tyres should be kept at the maximum pressure permitted for load and type and should be meticulously maintained. If any doubt exists around your tyres please consult your tyre specialist.

THE TOWBAR

The towbar, together with its ball, is a very important component and only a proprietary type approved by the vehicle manufacturer should be used. As some modern vehicles are extremely difficult to adapt. It is suggested that the towbar be professionally fitted.

The towbar:

  •   Carries the front of the caravan/trailer.
  •   Tows the caravan/trailer, and
  •   Often supplies a means of braking.

As the towbar carries the front of the caravan/trailer, the weight of the caravan/trailer is transferred, via the towing assembly, to the towing vehicle. This transfer, albeit a necessary one, creates some issues.

These are:

  •   Weight/Mass transfer, and
  •   Torque transfer

Both are due to the “static towbar load”.

WEIGHT/MASS TRANSFER

The “static towbar load” is often as much as 10 – 15% of the total weight of the Caravan/trailer and could be up to 150kgs, where the laden weight of caravan/trailer is 1,000 kgs. This transfer can put a tremendous strain on the towing assembly of the vehicle. It can be very tempting to shift some of the weight behind the axel of the Caravan/trailer to counter-balance the heavy nose; however, this in itself is a very dangerous thing to do as it could result in swaying and snaking.

The “static towbar load” of the caravan/trailer presses down on the tow ball of the vehicle, pushing the rear of the vehicle downwards. This causes the rear springs of the vehicle to deflect giving the vehicle a “tail down” attitude. Spring assisters, extra springs and appropriate shock absorbers can rectify this part of the problem; however, there is a second, and possibly more important, problem to consider. That is “torque transfer”.

TORQUE TRANSFER

Picture this if you will, rest a plank on two trestles placed two meters apart with one plank overhanging one trestle by about one meter. Now press down on the overhanging plank, the other end lifts off of the trestle. This is very much the same situation as a caravan/trailer pressing down on the tow ball of a vehicle. The tow ball is set a considerable distance behind the rear axle; therefore, the tendency is for the vehicle to pivot around the rear axle, Tail down – nose up.

To rectify this problem “torsion bars” are required. They range from simple torsion bar or anti sway bar to sophisticated “weight distribution hitches”. The principle behind all of these is the same. The tow bar is lifted near the ball and the vehicle pivoted around its rear axle to press the front end back to the ground. As the rear of the bar is carried by the caravan/trailer chassis, some of the torque is transferred to the wheels of the caravan/trailer.

Do not put too much tension on the bars or you will affect the vertical articulation between vehicle and caravan/trailer. Too little tension results in pitching on an undulating road. Experimentation with the tension of the transfer bars is well worth the effort. 

WEIGHT DISTRIBUTION HITCHES

This type of hitch is strongly recommended for heavy caravan/trailer. The hitch counteracts the effect of torque transfer as well as helping to distribute the transferred weight throughout the suspension of the towing vehicle and the caravan/trailer. This better weight distribution greatly enhances the steering characteristics of heavy car/caravan combinations.

ANTI–SWAY DEVICES

Caravan/trailer sway is usually caused by incompatible car/van combinations, incorrect loading, incorrect tyre pressure or driving error. An anti – sway device may consist of springs on the end of the torsion bars, cams between the torsion bars and caravan chassis, friction controls or hydraulic dampers between the vehicle towbar and caravan/trailer chassis. The aim of such devices is to prevent rapid oscillation of the caravan/trailer in a horizontal plane. Several “weight distribution hitches” and “anti-sway” devices are available as combined single units.

THE CARAVAN

Your caravan should be chosen with great care so as to be compatible with the towing vehicle. Seek expert advice when selecting your caravan/vehicle combination.

CARAVAN WEIGHT

The laden weight of the caravan/trailer must be within the limits acceptable to the towing vehicle. Take into account the weight of your load, including water, clothing, food, gas bottles etc. This can often add 100kgs + to the unladen weight. The fully laden “static towbar load” must be considered, as this is the load which is directly imposed on the rear axle of the towing vehicle. The best way to accurately gauge the load is to go to a public weighbridge.

Allowance for the weight of the caravan must be made when accelerating, braking and turning. Acceleration and ascending a hill will be much slower with the van attached, and braking will take much more time and distance. On hilly roads use your gears to keep the engine running freely. If you have an auto gearbox it may be necessary to engage a lower gear manually when ascending and descending hills. Do not let your engine labour under heavy loads at low speeds.

CARAVAN HEIGHT

Caravans come in a wide variety of heights and should be judged from your own personal preference. Fixed height vans (conventional) offer some advantages of heat insulation, noise insulation and accessibility en-route. This is paid for in slightly higher fuel cost and poor accessibility under cover parking, low trees etc. “Low-tow” types offer most of the advantages of conventional types with good access to low areas and improved fuel economy although access en-route is not so good. “Pop tops” offer a height advantage for access under car ports and low trees etc. “Camper trailers” have the advantage of being light for towing and quite low and more fuel efficient. Some vans/trailers are specially designed to be towed by four wheel (off road) vehicles.

The height of the van can cause some problems to the inexperienced caravaner. Take care when driving neat trees, road side signs and posts. Be careful when pulling up at curbs or tight turns in some country towns as the shop verandas are often built out to the curb edge causing damage to your van and the veranda.

CARAVAN WIDTH

The caravan/trailer can be wider than the towing vehicle, this can cause issues in traffic and on country roads. Allow plenty of room on both sides if the caravan/trailer especially when turning or lane changing. Vision will be limited so get some extended mirrors and check both mirrors and blind spots before manoeuvring.

If the left wheels drop off the bitumen when on a country road don’t panic, hold the steering wheel firmly, steer straight ahead and lower your speed gently by easing off the accelerator. When your speed has dropped return to the bitumen gently and smoothly and avoid   any sharp, jerky movements of the steering wheel. Avoid applying the brakes as there is usually very little, if any, danger in dropping a wheel off the bitumen.

CARAVAN LENGTH

A vehicle/caravan combination can be a long vehicle. That is a vehicle over eight meters in length or one towing a trailer. Most states have rules/regulations which forbid “long vehicles” travelling too close together on open roads as staying well apart permits faster traffic to overtake more easily. When overtaking or being overtaken, take the extra length into account. When turning remember that the caravan/trailer will “cut in” (take a slightly tighter line) and that the longer the caravan/trailer the greater degree of “cut in”.

BENDS

The rules for taking bends safely are the same for a solo vehicle and one which is towing a Caravan/trailer. As the margin for error is less when towing it is worth repeating these rules.

The approach to a right hand bend should be made as close in to the left as practicable. Whilst the approach to a left hand bend should be close to the centre of the road. This positioning allows the driver to see as far as possible into the bend and present the vehicle earlier to oncoming traffic. Exit from the bends should be close in to the left.

Your speed should be adjusted on the straight with all braking being completed early, gently and whilst travelling in a straight line. Any gear change to a lower gear should be made after braking and before the bend. If you adopt this method the car / caravan will be on the correct part of the road, travelling at the correct speed and in the correct gear engaged before you start your turn.

Gentle and progressive acceleration should be used throughout the bend to avoid any tendency to snake or pitch. Do not brake on a bend it can be very dangerous.

CARAVAN SWAY/SNAKING/FISHTAIL

Although this is not a common occurrence with the modern car / caravan combination its onset can be swift and frightening sometimes with disastrous results. The cause can be found in the car/ caravan combination which is incompatible; however, more often than not it lies in the poor loading of the caravan/trailer or in driving error.

The caravan/trailer should be loaded that the design parameters are met. In general this means that the load is kept at or near floor level and correctly distributed. Arguably, Most caravans are designed to carry 60% of the load forward of the axle and 40% behind the axle with heavier items as near to the axle as practicable. The load should be evenly distributed side to side.

Under NO circumstances should the load be placed at the rear of the caravan/trailer in an attempt to lessen the “nose” weight.

A novice driver can induce SWAY by attempting to steer a straight course with short rapid movements of the steering wheel. This occurs in cross winds or when the vehicle is struck by the bow wave of an oncoming or overtaking vehicle. The vehicle feels as though it is being blown off the road and the driver often responds too strongly. Sway may also occur when travelling on gravel roads or when crossing ridges left by graders or well-worn tracks. In all of these instances the driver should hold the steering wheel still and gently increase the power. This will result in the combination driving out of trouble. Do not apply the brakes.

A much more serious situation occurs when the driver has induced the sway by late and/or heavy braking on a bend. This type of sway can rapidly escalate into a “Jack – knife” situation with not much to do but hang on and hope for the best. It is essential that all braking be done while travelling in a straight line.

Sway is not a normal characteristic of the modern vehicle combinations. A driver/ car/caravan combination which is prone to sway should be examined by a professional to find the root cause.

 

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