That's a very interesting excerpt. It also points to a problem my father complains about fairly regularly. The drive up to his house is fairly steep.
When I was living there, it was straight up the side of the hill -- about 100 feet of 50+ % grade. At the time he was driving a couple of Mk I VW Rabbits and a Mk I Golf (FWD
). I had a pair of old Volvo 122s (RWD
). He found that he always had a harder time getting up the drive in the winter in the Rabbits then I did in the Volvo.
Being a physics major, he realized it was because the front end was getting too light. As you lift a car, more of the weight will shift to the rear wheels. It might be hard to thing of at first, but if you consider two limits (0 and 90 degrees of tilt), it makes sense.
Assuming you have a car of 50/50 weight distribution. At 0 degrees of fore/aft tilt, both front and rear axles have 50% of the weight on them. At 90 degrees tilt (with the front in the air) all of the weight of the car is on the rear axle, so the car has a 0/100% Front/Rear weight distribution.
If we take tract to be weight x adhesion, then in the first case, the 90 degree case, the front wheels will have no traction. Thus, in a front wheel drive car, you will not go anywhere.
[I cut some corners in my explanation, but I think it is enough for a brief overview.]