Up here in the northern hemisphere we're well into the cold season now, and I do get asked from time to time what my thoughts are on snow tyres. I've posted about this before but it's timely to mention it again.
Snow tyres are denoted by an M+S sign on the sidewall, or an embossed snowflake symbol. They differ from all-season or summer tyres in two main ways. First, the rubber compound is much softer, and second, the tread has a lot more siping in it (the thin cuts in the tread). The softer rubber compound means the tyre can maintain its flexibility at much lower temperatures, and the extra siping allows the tyre to have a lot more surface area for gripping loose surfaces. Packed snow is where you'll really notice a difference with winter tyres. Whilst they won't perform like summer tyres on a dry road, they'll outperform any summer or all-season setup with ease. 4-wheel drive or all-wheel-drive isn't enough in these sorts of conditions, and when it comes to braking, it doesn't matter if you have 4WD or AWD - what matters is whether or not the tyres can cope.
Where I live we regularly get snowy, icy winters, and even when the main roads have been plowed, the side streets are often a mess of rutted, packed down snow. For me, it makes complete sense to have snow tyres. But what about if you live somewhere like England where you only really get snow on the roads a couple of times a year? Snow tyres are actually still a worthwhile investment because they're also much better in lower temperature conditions. So even if the road isn't covered in snow, if it's cold and wet - in icy winter's morning in the UK for example - there's still a lot of benefit to be had.
The one thing to be careful of with snow tyres is the time of year. Generally speaking, unless you live somewhere with extremes of weather, you shouldn't run these tyres much after April, or before November. In warmer weather, the soft compound will wear extremely quickly. It's not unsafe, but it is burning money for no reason (the extra tread complexity and grip reduces your mpg). The ideal setup is a set of snow tyres for the winter months, and regular tyres for the rest of the year. It might seem expensive but think about this : the winter tyres will last 4 or 5 winters because they're not getting much use. So whilst paying for them this year will cost you some cash, for the next 4 years you've basically got 'free' winter tyres.
For most drivers, the idea of extra tyres for one season is a really hard sell. But just try it. I guarantee once you've done it once, you'll never go back to using all-season, or summer tyres in the winter months.