Everybody knows that an increase in a car’s weight has a direct effect on fuel consumption.
But there is no simple formula to calculate the additional fuel quantity required for every 10kg increase in weight.
However, based on tests done by carmakers, environment agencies and traffic management authorities, every 5 percent increase in weight results in a 2 percent increase in fuel consumption.
CALCULATING HOW WEIGHT AFFECTS FUEL CONSUMPTION
The best method to determine the effect of weight on economy is for you to run your own trials.
However, placing a 10kg deadweight in your car and recording the change in fuel economy probably won’t work. The difference in this scenario is unlikely to be measurable.
A better method would be to work out the increase in weight as a percentage of your car’s “test” weight. This means the vehicle’s kerb weight plus your own.
For a meaningful difference in fuel economy to be observed, this additional weight needs to be at least 5 percent of the “test” weight.
Let’s assume that your car weighs 1300kg and you are 70kg. An additional occupant roughly your size would be a 5 percent increase.
IS THIS THE IDEAL METHOD?
This method looks sound on paper, but it may not work in real life.
The difficulty in conducting these trials is ensuring similar conditions on a route over a distance of at least 100km. You must clock a longer distance if you want higher accuracy.
Such fuel consumption trials are not easy to conduct. There are too many variables beyond your control, such as ambient temperature and traffic conditions.
Other variables include your driving style and the state of your car. For instance, if it’s not regularly serviced, the fuel consumption figures are probably higher to begin with.