Up until 30th April 2021, the “energy” label of a tyre included three basic parameters: its energy efficiency in terms of rolling resistance (and thus fuel consumption), wet grip and external noise. These were parameters for performance indicating the “efficiency” of a tyre in very similar terms to that of electrical domestic appliances.
With the entry into force of the new standard with effect from 1st May 2021 (EU Regulation 2020/74), several items have changed, starting with the hitherto unpublished pictogram for adherence on ice/snow, which will be visible on tyres destined for particularly severe winter climates, where layers of ice/snow can occur on the ground.
Also worth reading: Tyres, and how to interpret the new European labelling
The scale of scores
As a general principle they have tried to create a label which is always more than just an identity card, with the obligation on the part of the manufacturer to input every detail into a European database - EPREL - and which offers the advantage for the consumer to be able to find out a lot more about the model chosen or to be purchased.
At the top and on the right hand side of the label, there is a QR Code which can be scanned using the camera of a smartphone, and which takes you to the product page within the above-mentioned European database. Everything is in a standard format, and this allows a much simpler comparison between different products.
From the performance point of view, the classifications – be they for energy efficiency or for wet grip – are five in number, ranging from A (the most efficient) to E (the least efficient). In addition to these criteria, the label now contains the new indication of external rolling noise. Let us examine them one by one.
Rolling resistance
This is to be interpreted as the force which the tyre opposes to its movement. When a car moves, the greatest proportion of its resistance to forward movement is caused by its aerodynamic resistance (around 60%); some 20% is made up of the mechanical resistance of the vehicle, whilst the remaining 20% is attributable to the rolling resistance imprinted by the tyres. The greater the rolling resistance of the tyres, the greater the quantity of fuel required to enable the vehicle to move. It may seem strange but on average 20% of fuel consumed, which corresponds to one full tank in five, is burned up in countering this effect.
In order to assign its classification, the measurements of the tyre are carried out in a laboratory, on a road tyre. They measure the drag force generated by the tyre during a straight-line run at a speed of 80 km/h and under the loads and pressures set out under a European standard.
They then calculate the coefficient of resistance to rolling (technically the CRR, valued in terms of Newtons/kNewton) of what is the ratio between the drag forces measured and the load applied to the tyre. Thus a model from class A (the top rating, for a car) has a score equal to or less than 6.5 N/kN and this goes down to class E – the lowest acceptable – which has a score in excess of 10.5 N/kN. By way of providing another measure for comparison purposes, a tyre from class A, in comparison to one of class E, consumes approximately 6 litres of fuel less for every 1,000 km travelled.
The wet grip index
It is clearer for drivers to understand how important it is to have tyres which “hold the road” in conditions where the tarmac is slippery or wet. The classification is allocated on the basis of results from tests on the track: the new tyre is mounted on a trolley pulled by a vehicle, which drives round at a constant speed (65 km/h), under specific load and pressure conditions, defined, as ever, by a European Community standard.
During this drive, the tyre is braked and the maximum force which it is able to generate is measured. The same measurement process is applied to a reference tyre, i.e. one which has already been “certified” under the standard. The relationship between the normalised braking force applied to the tyre being measured and that of the standard tyre represents the wet grip index. The higher the Wet Grip Index, the better will be the ability of the tyre to react in complicated situations: class A has a WG greater than 1.55, class B between 1.40 and 1.54, and so on until you arrive at E with a WG lower than or equal to 1.09.
External rolling noise
In this case, it is not a question of security but of comfort, which is nevertheless far from being a secondary issue. This is because the rolling sound of the tyres can be a nuisance not just for the driver and their passengers but also for people who live in areas with a lot of traffic. The reason? During a straight-line drive, the casing of a tyre emits noise as a result of phenomena linked to vibrations and the movement of air. Therefore the index appearing on the new EU label expresses in dB (A) – decibels A - the degree of quietness or otherwise of the tyre.
In order to ascertain this, they mount the tyre on a car on the track, measuring the noise level emitted during the trajectory, with the engine turned off, along a straight line at 80 km/h and under the conditions of load and pressure, as set down by the European standards. The maximum admissible limits and relative grading depend upon the width of the tyre. Thus, taking as an example a tyre with a width of 335, for standard tyres, grade B predicates a noise level of between 72 Db (A) and 74 dB (A) and a grade A of below 71 dB (A) whereas for “reinforced” tyres and/or 3MPSF the values change respectively from between 73 and 75 dB (A) for grade B and below 72 dB (A) for grade A. It should be noted that for both types, there are just 3 decibels (A) separating the quietest grade A from those of grade B.
