If you have summer performance tires on your car, here is information for you regarding tire compounds and winter tires. This information was composed from posts on Audiworld.
One word -- "Get Winter Tires" -- Ok, it was three words. :)
Get some decent all seasons (or, something like Dunlop Winter sports if you want extra-ordinary snow performance and decent wet/dry cold weather performance) on a winter set of wheels.
It is not question of AWD/ESP or not. The performance summer tires have a compound and tread design that makes them dangerous for real winter driving -- we're talking snow and ice and cold here and not some minor nuisance like a little bit of slush on some well plowed/salted/sanded roads. The performance tire big blocky treads are missing the numerous smaller teeth required to bite into snow. Add that to a tire compound that gets hard as a rock when the temperature falls much below freezing (it's called "glassing up") and you have approximately zero traction. AWD and ESP and ABS help you make the most of available traction - but they don't create traction for you. Simple physics. Before I got the Dunlop Winter sports on my S4, if it snowed I started up my 95 Impala SS with real winter tires. Even with 255/50/17 all season tires that big torque rear wheel drive SS sedan did MUCH better in snow than the S4 with summer performance tires. Currently my 8L has the stock 17" all seasons for the winter (already on) and a Pilot sports on 18" BBS wheels (waiting in the garage to be cleaned and put away for the winter).
As others have already said -- you INCREASE tire pressure for snow - you want to force the tread to bite as opposed to allowing the tire to deform around any contours it encounters (it is driving off road on sand that you lower tire pressure, and that is to increase the tire footprint to avoid sinking into the sand).
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I found the original 245/45-18 Dunlop SP8000's frightening in even the lightest snowfall.
I picked up my S8 in Jan '01 and live in SW Pennsylvania, where weather is probably similar to yours. ESP worked to the extent that I stayed on the road, but the ESP light flashing while going around many corners was a frequent reminder that the car was on the edge. I mounted 245/45-18 Pirelli 210 winter tires on the orginal Avus wheels and used this as an excuse to get HRE wheels for the summer tires.
The 2nd Winter, traction in the snow with the Pirelli's was outstanding.
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The Pilot Sport A/S size 255/45 18's work great on my S-8. They are quiet, handle in dry conditions, and are great on wet roads!!!! I had a chance to try them on snow covered roads this weekend and was completely sold on them. Expensive? Yes!!
