The key is to know exactly when a specific tire will break traction, so you can stay just slightly below that point. This varies slightly depending on the tire rubber composition, tread, pressure, tire load and riding temperature. A softer tire with a sticky rubber will hold traction better then a harder tire, tread can affect how the tire handles water, although hydroplaning is usually not an issue for bicycles. Ride temperature can be a bigger factor the a lot of people realise. Between 7℃ and 25℃ it doesn't really matter much, above 25℃ a tire is likely to have better traction due to the rubber getting stickier. Below 7℃ though is a bigger problem, because the rubber will get harder reducing traction. Below freezing is another issue, because precipitation is often in the form of snow or worse. For snow a MTB type knobby tire is better, as long as the snow is fairly soft and the rubber is fairly soft, if it's hard packed then it can be like ice, for ice you need studded tires. For grapple or ice pellets, think of a few billion tiny ball bearings coated in grease, your better to get off the road until it either freezes solid, melts or is removed. I disagree with Msrs' Guinness, the slipperiest material known to man is not teflon (as they say), it's a rubber tire on wet ice.....

I live on the Bruce Peninsula and up here 98 out of 100 cars get snow tires mounted, and the other 2 just don't have them on yet. I don't have them on my mountain bike, but expect to get them after Christmas....