Choosing a caravan tow vehicle
When choosing a caravan tow vehicle there are four key towing specifications that you need to know. This article explains what they are and why they are vital.
It is important that your caravan or trailer does not exceed these specifications. These are:
Choosing a Caravan Tow Vehicle – Maximum Towing Capacity
Vehicle makers stipulate two towing capacities: for trailers that are braked and unbraked. The braked towing capacity is much higher than if unbraked.
Apart from braking, a vehicle’s maximum towing capacity is in effect what it can pull on the end of a rope. It relates to matters such as its ability to stop and restart on a specified gradient etc. This ensures it has adequate power and torque. That overlooked by many caravaneers is the tow vehicle market is military and trades-people. Their typical trailer is short and rarely over 4 metres (about 9 feet).
Towball Mass – to be stable at all speeds a trailer must be nose heavy. The percentage of trailer weight required relates to trailer length. Most 4-metre trailers need only 5-6%. Many caravans, however, are longer.
Vehicle makers stipulate the maximum down-force that may be placed on the rear of the vehicle. This is a trap for new buyers. The required down-force of a three-tonne caravan (say 300 kg) may exceed the limit of the tow vehicle.
Choosing a Caravan Tow Vehicle – Tow ball mass is safe-speed related
Few caravaneers (even caravan makers) are aware that tow ball is speed-related. Other factors are involved, but the lower that (percentage) mass, the lower that safe speed.
NOT a recommended tow vehicle for this caravan… Pic: From ‘Free to Roam’ by John Swerder
In 2015 many local caravan makers launched twin-axle two-tonne plus products. From that year on, caravan jackknifing and rollovers escalated.
In one week alone (in mid-2018) there were three caravan rollovers on Queensland’s Bruce Highway. A few days later one rolled over on the Reid Highway (WA). Another on QLd’s Stuart Highway.
As noted above, a vehicle’s maximum towing capacity in effect relates to pulling a load at the end of a cable. It does not take into account the effects of trailer dimensions, side forces, load distribution or overhung hitches. Nor does take into account tyre types and pressures or suspension, chassis, tow bar and hitch construction. Caravan towing is a tiny percentage of vehicles that tow.
For caravan towing it is strongly recommended that its laden trailer weight is below the maximum towing capacity of the tow vehicle. Both RV Books and the user-oriented Caravan Council of Australia, recommend the laden caravan ideally be no more than 80% of the tow vehicle’s laden weight. That is the practice in the UK and most EU countries. It is despite most having an 80 km/h towing speed limit. Most caravans, in Australia, however, are far heavier than the laden tow vehicle.
Wheelbase to Hitch Overhang Ratio
When choosing a tow vehicle, there are two often-overlooked considerations. One is the distance between the vehicle’s front axle to rear axle. The longer that is, the better. The second is its rear overhang (distance from the rear axle to the tow ball). The shorter the better.
Most of the more popular Australian tow vehicles have a wheelbase of less than 2.9 metres and a rear overhang of (typically) 1.24 metre. This is a ratio of 2.234. A typical US tow vehicle, e.g. a Chevrolet Silverado, has a wheelbase of about 3.6 metres. Its rear overhang is 1.25 metre. This is a ratio of 2.88. That difference makes a major improvement in towing stability (the effect is not just linear).
A major legal limitation is the Gross Combined Mass (GCM). This is the maximum legally permissible laden mass of the tow vehicle and trailer combined. Its is typically 5500-6500 kg. GCM relates to all tow vehicles and trailers. That combination may be safe for a tradie towing a short trailer full of concrete blocks via a dual-cab ute. This is very different from that vehicle towing a seven metre plus 3000 kg caravan.
While 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.