Choosing a Caravan Tow Vehicle

NOT a recommended tow vehicle for this caravan... - Pic: From 'Free to Roam' by John Swerder
NOT a recommended tow vehicle for this caravan...

Pic: From 'Free to Roam' by John Swerder

Choosing a caravan tow vehicle - tow vehicle capacities

There are four key vehicle specifications that you need to know when choosing a caravan tow vehicle. These are not always easy to find, so RV Books has provided a list of towing specifications for some popular tow vehicles below.

It is important that your caravan or trailer does not exceed ANY of these specifications. These are:

  • Maximum Towing Capacity - this is the maximum weight that a tow vehicle may legally tow. That legal weight primarily relates to the tow vehicle's ability to stop and restart on a specified gradient etc. In effect it is what that tow vehicle is capable of pulling on the end of a rope. It may or may not be that imposed on an overhung hitch. This automatically ensures the engine has adequate power and torque.
  • Tow vehicle manufacturers normally stipulate two towing capacities - for trailers that are braked and unbraked. Braked trailer towing capacity is generally much higher than if unbraked, because a braked trailer's brakes help to stop the trailer and reduce the forces imposed by the trailer on the tow vehicle.
  • Maximum Towball Mass - this is the maximum amount of downwards force that may be placed by the trailer on the towball of the tow vehicle. This trips up some new buyers, because the required downwards force of the trailer (usually about 10% of the trailer's laden weight) can exceed the (sometimes modest) towball mass limit of the tow vehicle. Inadequate tow ball mass reduces the speed at which a trailer becomes seriously unstable.
  • Gross Vehicle Mass ('GVM') - this is the maximum permissible laden mass of the tow vehicle including all optional equipment, luggage, passengers AND any downward force imposed by the trailer on the tow ball. When towing, you must make sure that tow ball mass is taken into account when loading your tow vehicle.
  • Gross Combined Mass ('GCM') - this is the maximum permissible laden mass of the tow vehicle AND trailer combined. See 'The GCM Trap' below.

Note re tow bars - If, when choosing a tow vehicle - it has a tow bar fitted that was not manufactured and installed by the tow vehicle manufacturer, check its maximum towing capacity. It may be lower than the maximum towing capacity of the tow vehicle. If so, this lower limit is the maximum towing capacity for that tow vehicle whilst using that tow bar.

Choosing a Caravan Tow Vehicle - can I tow to maximum towing limits?

RV Books strongly recommends against towing up to your tow vehicle and caravan's legally permitted limits. This is not least as current legislation in based on an era when (according to the Australian Bureau of Statistics), the average age of our caravans was under 1400 kg and tow vehicles had far less power.

Tow vehicle maximum towing capacities are derived from manufacturers’ towing tests that (as noted above) in effect refer to pulling a fixed load at the end of a cable, and ensure the ability to restart on a steep hill of specified gradient. They do not take into account towing dynamics such as the effects of trailer dimensions, side forces, load distribution, overhung hitches, tyre types and pressures or suspension, chassis, tow bar and hitch construction.

For this reason it is strongly recommended that laden trailer weights are well below the maximum towing capacity of the tow vehicle. Both RV Books and the user-oriented Caravan Council of Australia, recommend the laden caravan be no more than 80% of the tow vehicle’s laden weight. That is the practice in the UK and most EU countries - despite most having an 80 km/h towing speed limit. 

Read more about recommended tow vehicle to trailer weight ratios here.

Choosing a Caravan Tow Vehicle - the GCM Trap

The Gross Combined Mass (GCM), is the maximum legally permissible laden weight of your laden caravan tow vehicle and laden trailer combined.

It cannot be assumed that a tow vehicle's GCM is the same as its claimed maximum towing capacity plus the GVM (Gross Vehicle Mass) of the caravan tow vehicle. With some Australian tow vehicles (in particular dual cab utes) it is less. As shown in the table below, the total of claimed maximum towing capacity plus GVM for many dual cab utes exceeds GCM by several hundred kilograms.

As most tow vehicle makers claim it, a maximum towing capacity of 3500 kg is presumably seen as desirable. It is (in RV Book's opinion) misleadingly used to attract buyers. With virtually all fully laden caravan tow vehicles (and particularly dual cab utes) the caravan tow vehicle's GCM renders it far less. This causes owners aware of the regulations to tow 3500 kg caravans with utes that are virtually unladen. This is seriously dangerous.Most legally fully laden dual cab utes are legally limited to towing about 3000 kg.  

Tow vehicles where maximum towing capacity plus GVM exceeds GCM are highlighted in grey in the table below. For these vehicles either maximum towing capacity and/or GVM must be reduced by the excess amount in order to meet the GCM.

Wheelbase to Hitch Overhang Ratio

A major consideration is the ratio of the tow vehicle wheelbase, i.e. the distance from its front axle to its rear axle to its rear overhang (i.e distance from its rear axle to the tow ball). The greater that ratio the more stable that vehicle will be when towing.

Most of the more popular Australian tow vehicles have a wheelbase of less than 2.9 metre and a rear overhang of (typically) 1.24 metre: a ratio of 2.234.  A typical US dual cab tow vehicle such as the Chevrolet Silverado has a wheelbase of about 3.6 metres yet a rear overhang of about 1.25 metre. This is a ratio of 2.88. That difference makes a major improvement in towing stability as the effect is not linear.

Whilst not an issue re choosing the tow vehicle, the tow hitch too must be as short as possible. A few on the market are longer than they need to be (to seemingly aid coupling and uncoupling. The rig's stability is far more important.

Choosing a Caravan Tow Vehicle - Tow Capacity Table

Below are the key towing capacities of some popular (2018) Australian tow vehicles. The maximum towing capacity show is braked trailer capacity only - if your trailer does not have brakes, please refer to the tow vehicle manufacturer to ascertain each vehicle's unbraked towing capacity. Refer above for definitions of GVM and GCM.


Notes

  1. Specifications are for Australian vehicles only and are subject to change. Check with manufacturer before making a purchasing decision.
  2. The table is a general guide only. Towing specifications may vary within model ranges and depends on engine size, engine type and transmission type.
  3. Data relates to current (2018) models only. Older or newer models may have different towing capacities.
  4. Maximum braked towing capacities include heavy duty towing options where available.
  5. Where a weight range is shown, towing capacity varies with trailer mass.
  6. Sources: manufacturer's websites, redbook.com.au, carsales.com.au.

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