The effect of load on behaviour, consumption and safety

But what is the effect of load on behaviour, consumption and safety?

1. Load and behaviour

   Carrying loads means increasing weight, which has three immediate consequences on vehicle behaviour and manoeuvrability:

   • Increased weight/power ratio;
   • Change in weight distribution;
   • Impact on the positioning of the centre of gravity at a height.

   The increase in the weight/power ratio means that the engine has to produce more work, so there is a reduction in performance proportional to the weight of the cargo loaded, as well as a corresponding increase in consumption: 50 kg of load does not have a significant effect on general behaviour but 500 kg of load will produce clear differences in the vehicle's response, both in terms of slower acceleration and recovery, but also in the reduction of braking capacity (by increasing the braking distance).

   By modifying the weight distribution, it will have a direct impact on the positioning of the vehicle's centre of gravity, both horizontally and vertically, which will affect the vehicle's stability, namely its ability to take bends.

2. Load and consumption

   The consumption of a vehicle is determined by the amount of work that the engine has to do when moving, in other words, the average power that we have to use. And the amount of power needed is determined by speed and weight. So the greater the speed and weight, the greater the consumption.

   Moreover, weight is so decisive for consumption that, whenever possible, designing routes in such a way that the vehicle travels the least possible distance with high weights results in large reductions in operating costs. And it's not just in terms of fuel savings: more weight means more wear on tyres, brakes, suspension and, as a general rule, on all mechanical components. To be precise, when driving a commercial vehicle close to its maximum permissible weight, it is normal for consumption to increase by between 50% and 100% compared to values obtained without load or with light loads.

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   The effect of weight on consumption is so high that driving adapted to this situation can result in significant savings. For example, learning to use gradients is one such technique. In other words, within the limits of safety, speed, and traffic conditions, the use of descents to increase speed instead of the accelerator, so that the kinetic energy or momentum accumulated helps to overcome the unfavourable slope without the need to accelerate more or reduce to a lower gear; in this particular example, with heavy loads, it is essential to optimise the gear selection and keep the engine speed in its maximum torque zone and best efficiency.

   On the other hand, adopting preventive and predictive driving, reducing as much as possible the use of acceleration to regain speed and the use of brakes to reduce it, always ends up resulting in lower consumption and savings. In practice, the driver, who most of the time is familiar with the routes used, can use traffic and intersections, traffic lights, bends and roundabouts in order to be, whenever possible, at the right speed for each moment/situation without having to promote unnecessary acceleration or braking. In addition to the cost reduction that this allows, another great benefit is the increase in road safety.

3. Load and safety

   Load increases weight and a heavier vehicle behaves worse in aerodynamic terms; the greater the weight gain, the greater the degradation we should expect. This means that it is slower to accelerate, needs more metres to stop, loses stability on bends and poor road surfaces, having more inertia and less agility, all of which are aspects that detract from the ability to perform emergency manoeuvres and make it difficult to carry them out in controlled fashion. In other words, a loaded, heavy vehicle has reduced dynamic safety, thus requiring driving adapted to these circumstances.

   Now, today all new vehicles sold have traction and stability controls as standard. All of this equipment represents safety gains and driving aids, facilitating control by the driver in the event of unforeseen situations. So, if the load reduces the vehicle's ability to react quickly, it is very important to anticipate rather than react.