Winter tyres ? don?t rely on the M+S mark! » Oponeo.co.uk
What does a tyre have to do to become approved for winter use?
The detailed guidelines that enable a tyre to be classed as suitable for use in winter conditions are contained in the Corrigendum to UN ECE Regulation 117. This amendment requires that winter tyres demonstrate a specified level of performance on snow. Tyres are subjected to a braking test or a traction test. Only tyres that pass the test are allowed to carry the 3PMSF mark.
What happens in the test?
The regulations referred to above lay down a specific method by which tyres are to be tested. It has the rather complex name of “mean fully developed deceleration”, or MFDD.
In the test, the distance travelled is measured as a vehicle with ABS decelerates between two defined speeds (from 25 km/h to 10 km/h in the case of the test on snow), and then the snow grip index is calculated relative to a standard reference test tyre (SRTT). In practice, the test reveals whether and to what extent the tyre skids during deceleration.
The reference tyre is a tyre produced, controlled and stored in accordance with the relevant standard E1136-93 (2003), published by the United States standards organization ASTM.
What are the conditions for testing this type of tyre?
The test should be carried out on a level test track of compacted snow, with a maximum gradient of 2°, and of sufficient length and breadth. The snow layer must consist of:
a heavily compacted lower layer with a thickness of at least 3 cm;
an upper layer with a thickness of approximately 2 cm.
During the test, the air temperature one metre above ground should be between –2°C and –15°C, and the temperature of the snow, measured at a depth of approximately 1 cm, should be between 4°C and –15°C. It is recommended to avoid strong wind and sunlight, as well as variation in sunlight and humidity during the test and between different locations in the test zone.
How are the results interpreted?
For a tyre to be classed as a winter tyre suitable for use in tough snowy conditions, and to carry the three-peak mountain snowflake symbol, it must have a snow grip index, relative to the reference tyre, of at least:
1.07 (i.e. better by 7%) in the case of C1 category tyres (car tyres);
1.02 (i.e. better by 2%) in the case of C2 category tyres (goods vehicle tyres).
This index is defined as the ratio of the result obtained by the tested tyre to that obtained by the standard reference tyre.
The snow grip index may also be determined using a method that measures traction in snow, in accordance with the ASTM F 1805-06 standard. In this case the tyre must attain an index of 1.10, which means it needs to be 10% better than the reference tyre.
Unfortunately the exact results of the tests are not published, so it is not known which models achieved the best results in official testing. Information about the performance of particular
The table below shows the minimum snow grip index values that a winter tyre is required to attain.
Tire class Snow grip index value (braking) Snow grip index value (traction)
Example of a tyre SRTT 14 SRTT 16C SRTT 14
C1 (car tyres) 1,07 - 1,10
C2 (goods vehicle tyres) - 1,02 1,10
In 1999, The U.S. Rubber Manufacturers Association (RMA) and the Rubber Association of Canada (RAC) agreed on a performance based standard to identify passenger and light truck tires that attain a traction index equal to, or greater than 110 (compared to a reference tire which is rated 100) during the specified American Society for Testing and Materials traction tests on packed snow.