Well, summer’s here (or at least, August is), and many readers will be hitching up their touring caravans and heading for holiday destinations, at home and abroad. Diesel power, of course, is always the right choice for towing! But with current fuel prices and the extra load on your car when towing, fuel costs become a significant item on any holiday budget – up to 25p a mile, and maybe £700 in fuel for a two-week touring holiday. So eking every mile you can from your diesel is well worth thinking about.
Speed is really the key to good towing economy, because aerodynamics is a huge factor when towing something like a caravan, compared with an unhitched car. It’s down to the bluff shape of the typical caravan, and the drag-inducing turbulence that exists in the area between the rear of the car and the caravan. Aerodynamic aids to towing economy have been offered over the years, (veterans may remember the Windslammer) and Purple Line still offer a roof-mounted, drag-reducing device, but reports on their effectiveness are rather mixed. Air resistance rises with the square of the speed, so cruising at 60mph (on dual carriageways) uses up to 40 per cent more fuel than at 50mph. Caravanners present a better image when allowing decent opportunities for other traffic to pass more easily, and legally, and cruising at close to your legal limit, (10mph slower than for cars) is sometimes not very helpful. Dropping back by 5mph and leaving a decent gap to slower vehicles ahead gives the cars more opportunity to pass, and you’ll be able to save big money.
Gear selection, acceleration and coping with hills are other key areas. Engines work best and most economically around their peak torque speed, generally around 2,000 to 2,500 rpm, even though manufacturers often quote lower engine speeds. Modern cars are geared for economy at high speeds and top gear is often too high for 50mph and sometimes 60mph towing, so the gear below top will often be your most economical choice. You’ll avoid having to drop a gear for every slight incline, and better engine braking is available on the overrun. Do use your gears for accelerating up to cruising speed though; you’ll get there quicker and use less fuel. With automatics, you may like to use the Sport selector or hold gears manually to get up to speed, and then slot into D for cruising, or manually select one gear lower than top, depending on engine speeds. We don’t advise using cruise control when towing, as engines may struggle on long uphill drags when it’s better for economy to change down and lose some speed, particularly if you’re getting in nobody’s way.
Don’t forget your tyres either, particularly if you’re towing with a four-wheel-drive fitted with all-weather tyres. Their rolling resistance is quite significant, and setting the right tyre pressures is always essential for optimum economy. The tyres and pressures on your ’van or trailer need checking carefully too. Anticipation is also important – you’ll always want to avoid fierce braking with a load behind, with the possible instability, so easing off the throttle early for roundabouts and other road situations saves fuel that might otherwise be wasted by your braking. Finally, as all towers will know, head winds and side winds are quite a pain and they will hit your fuel economy badly. Unless you’re in a desperate hurry, do slow down for both safety and fuel economy when you hit such conditions. A 10mph head wind does the same as cruising 10mph faster to fuel economy, so you can see the possible savings from slowing down.