Stay on course...
Understand the lingo of your GPS
What is best for towing: a manual or automatic gearbox? And is it true that you should never tow in fifth gear? There are a few unwritten rules around a campfire: you never, for example, tell a man what rugby team he should support or what car he ought to buy. And if you like your friends (and your front teeth), you will also never start a debate regarding automatic versus manual transmission – nor one about towing in fifth gear.
THE TORQUE CURVE
Towing is not merely a matter of pushing the accelerator to its limit in order to just get going. Even before you jump into the car, there is some necessary homework to do: consider the torque curve of your towing vehicle. If you fail to find the curve in the owner’s manual of the vehicle, then pay a quick visit to the internet and search for it there. Should you refer to torque, you need to know at what revolutions (r.p.m) the engine of your car functions optimally. For this purpose, you get a generic torque curve that resembles an arch.
Always try to tow in such a way that the performance of the engine falls in the top 20% of this curve. It is also in this percentage section that the engine runs cooler and more economically. In the remaining 80% if this curve, the engine labours in some way or another, whether it is during acceleration or because the revs are too high or too low. (By the way, when not towing, you should look at the upper 30% of the curve).
WHAT ABOUT FIFTH?
When you look at a five-speed gearbox, the fourth gear is often the one with a 1:1 gear ratio (or closest to it). In other words, the gearbox might just as well not have been there at all, since the rpms of the gearbox and the driver shaft are the same.
For some unknown reason, there is a myth that purports it is not a good idea for the gearbox to tow in fifth. However, there is no logical reason whatsoever for thinking along these lines. The fifth gear cannot simply break. A gear breaks when it has to work without oil and therefore overheats.
The fifth-gear myth probably originated in the seventies and early eighties when regular family cars were fitted with only four gears. At the time, fourth gear was also the 1:1 gear and was the one that you selected for towing. Subsequently, a fifth gear was added – the gear was known as the overdrive. (From first to third, the engine revs were more than that of the drive shaft. In fourth, it was the same, but in fifth, the drive shaft rotated faster than the engine – hence the name. Fifth gear was not intended to be a powerful gear but rather one to let your vehicle drive more economically.
Modern-day engines however, are so far advanced and so powerful that your vehicle can easily tow in fifth. In some of the sixgear boxes, fifth can be the 1:1 gear, but it is no longer a given that a gearbox has a 1:1 gear. It may be that the ratio of any gear is slightly higher or lower.
In principle, an automatic and a manual gearbox work exactly the same. Except for you having to step on a clutch with a manual transmission (an automatic gearbox has a mechanism inside it that does exactly the same job), the gears are identical. Some manufacturers actually recommend using an automatic gearbox when you want to tow anything heavy. An automatic gearbox also helps inexperienced towers to concentrate on their driving since they don’t have to worry about changing gears.
Going downhill is fine for coasting, but remain in gear. People err by selecting lower gears when going down a steep hill. Wear and tear on the gearbox is then the same as when you’re accelerating. Rather use the brakes to control your speed. That’s what they’re there for, after all. Keep the engine revs within the 20% zone when going downhill and, should the going get steeper, reduce speed by applying more brakes and gearing down sytematically. Do not take the car out of gear when going downhill. A vehicle weighing 2 tons accelerates faster that a racing car over a distance of 100 m and at a slope of 30 º .
If there’s an uphill stretch after the downhill, you’ll want to select the lower gear at the right time to climb the hill. Shift down at the bottom of the hill so that you reach the maximum revs in the 20% zone of the torque curve (for instance 2 280 r.p.m in the previous example). As you lose speed while ascending the hill, keep gearing down according to the 20% principle.
CHOOSE THE SAME TYRES
The size of the tyres on your vehicle has an immediate effect on the gear ratio of the gearbox relative to the speed at which you are driving.
When replacing tyres, it is important to keep the circumference of the new tyres within 10% of the original measurements. (It is best to stick to the original dimensions as the manufacturer intended.)
If, for example, you change from a 17” rim to an 18” one and the 17” tyre had a 75 mm profile, you will now have to fit a 60 mm profile tyre on the 18” rim. Some manufacturers’ warranty becomes void if you fit tyres exceed their specifications and even some insurance companies will refuse to honour your claim if anything goes wrong because of this.
Remember, not all cars are designed for towing. When you tow, there’s an additional burden on the gearbox, which can cause it to operate at higher temperatures. It is good for the oil and the gearbox if the oil remains cool. If you suspect that your gearbox is overheating, you can always consider fitting an oil cooler.
It’s also important to remember that oil ages. If you often tow a caravan, you should to replace the gearbox oil every 5 000 km.