Winter tyres.

[beam me up schottky]

Using winter tyres all year is not advised, they will wear much quicker at higher temperatures and drier conditions, and, I think I may be right in saying, that their speed rating is lower, so high speed use on motorways could be a problem.
After trying mine I realised I'd missed an obvious reason for using them when I had previously considered winter tyres, that is, in motor-sport it is normal practice to change tyres to suit conditions, particularly in Rallying !!