Tyres and security on the road - Labelling: Do winter tyres increase wet braking distances?
Center

Labelling: Do winter tyres increase wet braking distances?

Security Published the 28/01/2013 by Charlotte

That’s what can be read here and there on the web and what a quick review of tyre labels suggests. For sure, summer tyres generally have a better wet grip rating than winter tyres. But the test protocol defined by European regulations place the latter at a disadvantage. Before jumping to conclusions on the performance of winter tyres, take a look at the results of a study we conducted on over 15,000 labelled tyres.

Winter tyres breaking on wet ground Winter tyres breaking on wet ground - Copyright © : All Rights Reserved

Over the last few months, Rezulteo has systematically recorded tyre labels  published on Internet by tyre manufacturers and tyre retailers.  To date, on the basis of over 15,000 different tyres, this data has enabled us to determine which label is most frequently observed.

Wet grip: Summer tyres have better ratings than winter tyres

 

Distribution of labelling classes for summer tyres and winter tyres
Since the distribution was scattered, we have taken a cumulative presentation of results to emphasis the difference between winter tyres and summer tyres. Database: 15,000 tyres (Source: Rezulteo).

C-E: The axes of the graph represent the different combinations of classes recorded for two performance criteria: Wet grip (C) and fuel efficiency (E).

Distribution of labelling classes Copyright © : All Rights Reserved

We observe that the distribution of labels based on wet grip and fuel efficiency, the main tyre labelling criteria, reveals that summer tyres have a clear advantage over winter tyres.

Wet grip*

A

A-B

A-B-C

A-B-C-E

Summer tyre

10,3%

43,9%

89,5%

99,9%

Winter tyre

5,8%

11,3%

66,1%

97,3%

* Percentage of tyres falling into classes…

On the basis of wet grip, summer tyres generally obtain better scores. Almost 44% of summer tyres are rated A or B, compared with just over 11% for winter tyres. And almost 90% of summer tyres are rated A, B or C, compared with just over 66% for winter tyres.

So, does this mean that winter tyres take longer to stop on wet roads?

Certainly not. The performance difference compared with summer tyres is mainly due to how tests are conducted.

Indeed, winter tyres   are optimised for … winter conditions. In winter tyres, the compound and tread pattern (numerous sipes, deep treads …) are designed to provide maximum grip on cold, slippery surfaces and improve traction on snow and ice.

Yet the protocol set out by tyre labelling regulations stipulates that winter tyres tests should be performed at temperatures between  + 2° and + 20 °C. Since winter tyres deliver their optimum performance below 7°C, it is clear that the protocol tends to place winter tyres at a disadvantage.

This is true even more so for Nordic tyres,  designed for very low temperatures and snow covered and icy surfaces. For this type of tyre, wet grip efficiency is not the most relevant criterion.  This is the argument used by certain brands such as Nokian, specialised in this type of tyre.

Finally, it should be noted that studded tyres  do not fall within the scope of European tyre labelling. 

So, how do drivers select the right winter tyres?

These findings should encourage us to put the wet grip criteria into perspective when choosing winter tyres.  At the end of the day, the real question is whether it is better to have wet braking distances a few metres longer when temperatures are above 7°C or several tens of metres shorter on snow and ice? Only the consumer can answer this question depending on the region where he lives or the harshness of winter conditions…


Distribution of labelling classes based on brands 

Cumulative presentation of results. In this graph, the distribution of labelling classes shows three groups of brands:  

  • Leading or premium brands
  • Intermediate brands
  • Budget brands

Distribution of labelling classes based on brandsCopyright © : All Rights Reserved

Finally, if the distribution of winter tyres based on brands is considered, then for wet grip, leading brands obtain a better rating than intermediate or budget brands.  This is not surprising, since leading brands put a tremendous amount of work into balancing performances …