How fast should you go when towing?
When you’ve hitched up the van and are heading off on your first tour, or the next of many, you might be wondering what speed is right for towing.
There are plenty of laws about caravan weights, lights and even what distance you have to travel behind other vehicles, but none about speed. That is, of course, except for obeying posted speed limits and, in all states and territories, that means a maximum of 110km/h (except in Western Australia, where the maximum towing speed is 100km/h).
There is another speed limit, and that is the tow vehicle’s maximum allowed speed while towing. Some manufacturers limit permitted speed to less than the posted maximum, with many of these restricting towing speeds to a maximum of 80km/h – including Subaru and Holden, with older models such as the VY Series Commodore.
Others, such as Kia and Hyundai, do not place restrictions on speed for towing generally, but do when towing a heavy trailer up hills. Such manufacturers advise that speed should be reduced to 70km/h in these conditions.
The reasons for these restrictions are either the manufacturer has found in development testing that heavy-duty towing can put excessive strain on the powertrain and associated components at higher speeds, or with steeper inclines and/or towing, stability is found to be compromised at higher speeds. Rather than taking the risk of saying ‘use common sense’ and ‘don’t drive at a speed where you notice the vehicle is straining or feels unstable’, they use a blanket limit.
READ THE MANUAL
Buying a brand-new rig and planning to head off on tour the day after picking it up? Read the owner’s manual carefully, because you’ll find most manufacturers, while no longer requiring a running-in period for general driving, do require exactly that when towing with a new vehicle. Typically, you’ll have to drive at a restricted speed for the first 800-1500km (often it’s an 80km/h restriction), yet some manufacturers warn against towing at all when the vehicle is this new. Perhaps you’ll have to take a few trips solo to clock up the kilometres before you hitch up the van.
Looking at the owner’s manual for trailer towing requirements is one of the most important things you can do.
If you ignore such advice and cruise at a higher speed regardless (even if it’s the legal speed limit), if you crash or your vehicle suffers mechanical damage, you have, potentially, diminished legal recourse for repairs. Some vehicle manufacturers will not honour warranty claims if damage can be proven to be due to trailer towing. In the case of a crash, you may find yourself facing charges and an insurance claim refusal.
It may be difficult for other drivers to understand why you’re doing 80km/h in a 110km/h zone, especially if road conditions appear ideal, but this is your lot if you have a tow vehicle with such limits. In fast-moving traffic on multi-lane roads you have to be just as aware of what is going on around you and judge carefully as you’ll have vehicles approaching you a lot faster than you think. Good mirrors are a must.
Generally speaking, I find that a speed of about 90km/h is where I feel most comfortable on paved roads, provided that the vehicle and van are up to it (in respect of manufacturer’s nominated speed limits, road conditions/limits and vehicle stability). This speed is generally fast enough to feel as if you are not pushing the vehicle too hard and also a speed that allows you to keep out of the way of faster traffic more often than not. Overtaking slower vehicles, merging into traffic or leading a line of traffic, feels less of a compromise at this speed than when going slower on most highways/freeways.
What your vehicle and van are doing is only part of it, though; being able to react to changing road and traffic conditions is a key element to choosing that sweet spot touring speed. Your rig may feel absolutely safe at 100km/h, but what if you had to perform an evasive move? Dealing with a swaying caravan is a lot easier at a lower speed, and might be altogether avoided if speed is kept in check. Your rig might be able to cruise all day anywhere it’s legal at 110km/h, but how well will it all come to a halt in a hurry?
HITTING THE DIRT
Dirt roads are another thing entirely. While many dirt roads in the outback are smooth and straight – and theoretically you could quite easily travel at 100km/h – many are not. I would suggest you don’t travel more than 80km/h when towing on dirt roads and, even then, you’ll have to concentrate that much harder to check for a change in road conditions. Dirt road surfaces can, and often do, vary. Driving on the Oodnadatta Track a few years ago, the surface was dry but had obviously suffered damage from being driven on in the wet. The road surface went from smooth dirt on which you could cruise at 100km/h to undulations you needed to broach at 30km/h in order to not bottom out the suspension. It’s harder to ‘read’ a dirt road.
There is a grain of truth to the assertion that if you drive more slowly, your vehicle is more fuel-efficient. The Bosch Automotive Handbook says the speed at which aerodynamic drag overtakes mechanical drag for passenger cars is around 80km/h.
You’ll have to find the most efficient cruising speed for your rig by cruising at a set speed for a tankful and vary it for the next. This comparison assumes, of course, that you’re driving in similar conditions – a tankful of driving into a headwind is not comparable with one that is not.
You can get a better idea of fuel consumption on the run if your vehicle has a trip computer, or add an accessory version like the ScanGaugeII. You can check average fuel consumption to find the most fuel-efficient speed.
Like everything, cruising speed while towing is a compromise; you don’t want to feel as if you’re in danger of losing control of the rig, but you don’t want to become a dangerous obstruction to traffic either.
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The full feature appeared in Caravan World #546 December 2015. Subscribe today for the latest caravan reviews and news every month!