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Motoring: Easy does it – Driving to save fuel

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Motoring Editorial published in the June 2016 edition of The Billboard:

There’s no doubt that driving slower is just about the best way to use less fuel but this does not mean that you have to crawl along at a ridiculously low speed. Your driving habits can play a significant role but driving economically under all conditions requires some forethought. The following steps will turn you into an economical driver:

Reduce idling time

Drive off immediately after starting the car in the morning. Do not let it idle for any length of time. Go slow at first, to allow the engine, gearbox and final drive to warm up. Driving off will reduce the amount of time the engine has to inhale the over-rich fuel mixture required for starting and idling.

Stay with the traffic in town

At speeds below 60 km/h the car demands very little energy from the engine but the latter becomes very inefficient. If you slow down too much you will not only be an obstruction but you may also have to change down to a lower gear. A lower gear usually, but not always, means your vehicle will use more fuel.

Anticipate

One of the major differences between a good driver and a bad one is that the former exhibits a far greater degree of anticipation. Passengers become subconsciously aware of this because a bad driver brakes more often, and every time a car slows down some energy is wasted. To get up to cruising speed again requires more energy from the engine than the car would have required to remain at the former cruising speed. If you have to pick up speed do it slowly because the faster you accelerate the more fuel you use.

Cruise at slower speeds

Whenever a car maintains a constant speed on a level road the fact that no acceleration takes place indicates that the engine supplies just enough power to balance the sum of all the frictional forces trying to slow the car down. A higher cruising speed requires more power, because the frictional forces are greater. Air resistance supplies the biggest frictional component, and this increases as the square of the speed, meaning that the resistance at 100 km/h is four times as high it is at 50 km/h!

Think about the load

The load a car carries affects the fuel consumption in different ways, depending on how it is carried:

  • If the extra mass is inside the vehicle, this increases the total vehicle mass, so that the engine has to work harder to accelerate up to any speed. Driving in traffic or in a hilly country will show an increase in fuel consumption.
  • An inside load does not affect the air resistance so the fuel consumption will not change significantly when cruising on a level road at a constant speed.
  • An extra load carried on the roof or in a trailer will affect the fuel consumption in the same way as a load carried inside, but in addition will also increase the air resistance dramatically, so that it is far better to carry a load inside a vehicle than outside

 

Text supplied by Jake Venter

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