How are such tyres defined? Looking at tyres for the car, you get summer tyres, winter tyres, and 4 season tyres, in theory the definitions sound fine, but looking at a set of Vredestein Quadtracs but noticed different places refer to them as 4 season and winter, on the Vredestein website they are 4 season but are marked as M&S, so what is the definition?

I'm no expert but afaik full winter tyres should have the mountain + snowflake symbol. The refers to the thread pattern and the softer compounds used for low temps. You can use them all year but they will wear quicker in dry conditions.
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(a poor attempt at the symbol!)

4 season tyres are normal year round UK tyres. M+S labelled tyres will have a good thread for snow but possibly not the softer compound.

You can find some info on here (US related but you'll get the idea) including the usual snowflake and mountain winter symbol:
http://www.tirerack.com/winter/tech/techpage.jsp?techid=125

And a nice video to convince you of the advantages:
http://www.tirerack.com/videos/index.jsp?video=23

vredestein QUATRAC 2 and 3 have the mountain snowflake symbol so are winter tyres.

I've got Nokian WR tyres on my car (with the mountain and snowflake symbol) and they've worn about 2-3mm in 17,000 miles of driving, so I'm not so sure about the supposedly faster wear-rate 😕
Very very pleased with them though.

Sharkbait – Indeed I agree. But the that's the official advice. We're in the UK afterall. I drive in the mornings and night and the temps rarely go above 10deg. So I'm tempted to leave them on all the time.

I stuck some new wheels on a Clio with Vredestien Snowtrac tyres on them. These are more 'mountain' than the Quatracs as I believe the Quatracs are a half and half tyre from a tread perspective. Very, very impressed so far but the impression I get is that any of these tyres will work far better than the standard UK fit tyres that most cars have. As they're on a second set of wheels (16 inch Clio M+S tyres are a pig to find) I will switch over when it warms up. This is my first foray into winter tyres and I'm more than happy with my decision. Can fully recommend http://www.tyremen.co.uk too – Very helpful and prompt service.

There's tons of arguments for and against getting winter tyres but for me and the missus (and kids) it's piece of mind that we can go out AND get home again (Holme Valley in Yorkshire) and they'll last a long time and as wheelsets have some resale value. Would definitely recommend it.

There is a very weak definition of what an M+S tyre actually is.
It is something like, a tyre that is specifically designed for Mud & Snow….
Bit like comparing a supermarket mountain 'style' bike with a 'real' one.

Basically it is up to the tyre manufacturers if they 'believe' their tyre is suitable for such a marking. There are definitely some tyres marked as M&S that have rather limited winter performance. Winter performance comes from a combination of pattern, compound & construction whereas a mud tyre has less reliance on tread compound.

The snowflake marking is a US Federal marking. This means the tyre must pass a snow traction test to receive the marking though this is up to the manufacturer to confirm. As the penalties for 'being mistaken' (or lying) are rather high, if a tyre has the snowflake marking it can be normally considered as valid but this is only truly reliable in the US where the mark has some value. In Europe there is no test required to display the marking.

There are tyres available that are known as 4-season or all-season pattern. This means that they somewhere halfway between a summer & continental winter tyre. The typical snow performance for such a tyre means that passing the snowflake mark test is rather borderine.

So I'm tempted to leave them on all the time.

Mine are on all the time (XC90) if it makes a difference.

🙂