Quote:
Originally Posted by Foreigner500
>>By the way winter tyres are not only for snow.
What are the downsides of winter tyres when its not wet or snowing ? I guess trying to understand how practical it is to drive on them all winter when actually conditions might only be bad 20% of the time.
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Winter tyres are designed to be more flexible in winter conditions (below 7-8 degree C) that's why the rubber is softer. The main tread blocks are filed with very small cuts known as sipes (I refered to them as lamels).
Tread sipes create little biting edges that aid snow traction. The sipes bend away more easily because larger section of the tread is sliced/cut into smaller sections.
In normal summer tyre one of the blocks would be as a hole block whereas in winter tyres it's additionally cut for more flexibility and for this biting edge effect which more effectively removes snow, water or cuts through the ice when in contact with the boundary layer of either snow, ice or water - the tyre is more sticky you could say. The boundary layter is the most crucial part for the tyre to remove the obstacle (water, snow or ice). If it's not effective the tyre will lift off (I think it's called aqua-planning) and will be travelling over the water with no contact with the ground.
Additionaly when the expanded tread goes back to normal postion after the part of the tyre lost the contact with the ground (the wheel is rotating) then the excessive snow or water is pushed out from the tread. That's why with winter tyres you see the snow splashing away (the same with water but more difficult to spot) when the wheel is rotating.
A very general idea of winter tyre is like a pump which is pumping out the snow or water. It's the same thing with summer tyre but due to harder compound and less holes in the tread the water or snow removal is significantly less efficient. That's why quite often winter tyres are also narrower - it's more easy to remove the water or snow from a slimmer tyre sideways because most of the water is removed sideways anyway.
The winter tyres should be used only during winter season becasue due to softer compound you've got more grip which means there is more friction and this means lower fuel economy and higher wear.
I'm not sure to what 20% of bad conditions you're refering to. Winter tyre is also far better in wet conditions compared to summer tyre. There is a lot of rain and low temperatures in UK during winter.
That's a long explanation. I hope it makes sense.