True "winter" tyres (they have a three-peaked mountain and a snowflake symbol on the sidewall) start to deliver better grip than "Summer" tyres below about 7 degrees C. It doesn't have to be frosty or snowy. Obviously, it's barely noticeable at that temperature, but below about 3 degrees, most drivers can spot it. Certainly below freezing (which I admit, in Southern UK isn't that often), the difference is very noticeable. Some rear wheel drive cars put their power down better than others, as do some fronts. In general, front wheel drives have more of their weight over the driven wheels - which is the key. I have a front wheel drive car that is lousy in snow, because as a right hand drive, with driver-only, and an open diff, I'm sitting on the same side as the engine, so it just spins its left hand front wheel.