I've had several rear wheel drive cars (m3, 335i, 911, 135i) and snow tires are a must. I almost got stuck last week when it snowed 4" in northern nj. I left my office early and I only had a slight hill near my house. I stopped at the signal and then proceeded to slip and slide sideways and backwards. I turned off my DSC and floored it timing the light. Whew, got home safe. I was kicking myself for not putting on my snow tires.
Btw, saw an ad in 201 magazine for a snow tire storage service called Switch and Store (www.switchandstore.com
). I found some forum postings in a competing forum about them as well. Looks promising.