I get most of my information on car performance from Top Gear, so bear with me here.
The other night, there was a repeat of a test drive of the Jaguar X-Type 4wd estate. In mildly snowy (looked like a inch or so of snow on the ground) conditions, it was described as better than the front wheel drive vehicles it passed and a rear wheel drive car was described as “terrifying” in that weather.
Going up hill I could understand, weight transfers to the rear of the car, the rear wheels get more traction. Other than that, going downhill and around corners, the car didn’t seem to have any advantage other than the weight of the 4wd system pushing the wheels further down and improving traction perhaps, but in an inch of snow that seems really slight. And wouldn’t the rear spin away anyway?
Off road, I can understand the advantages of wheels that can grip and pull away whenever possible. On a road, it’s less clear. Top Gear itself tested a 4wd Audi, front wheel drive Alfa and rear wheel drive BMW to demonstrate the difference between them on a road. The Alfa understeered, the BMW oversteered, the Audi was inbetween the two and was described as having the best and worst of the other two transmissions. Other magazines have stated a preference for traction control, it keeps a car going round a corner without the extra weight of 4wd
The Jag didn’t seem to have any tricks either, not even snow chains.