what principles of physics explain the infamous "lift-off-oversteer" characteristics the Porsche 911s of yore

Question

The 911s have the engine sitting behind the rear axle, which results in a big REAR-WARD weight bias. My theory was always that - since 'inertia' is always proportional to mass, the rear end had higher inertia than the front end, and thus the rear end tends to want to move in a straight line tangential to the curve so it leaves the curve first.... i.e. the centrifugal force, so to speak....

Answer 1

While the difference in inertial momentum can describe some of the 911's handling characteristics in relation to quick turn-in and the difficulty in recovering from the end coming around, it doesn't explain it going around in the first place.

Lift-Off or Trailing Throttle Oversteer will happen in any car, and is the result of the car's balance shifting. The heavy rear weight bias in the 911 merely exagerates how quickly and unexpectedly this can happen.

If you look at a car, balanced on four wheels, you will see the weight shift opposite the direction of a turn when under side loading, or forwards or backwards when accelerating or braking (with lifting the throttle actually being braking due to the drive line slowing, and causing the weight to shift to the front wheels).

When the weight shifts, the wheels that go under load get more available traction, while the opposite wheels lose some. If you take a car that is at, or near the limits of traction in a turn, and then lift the throttle you suddenly have less traction than is needed to hold the car in place, while the front actually gains traction, so it will stay as is. The back then moves out, along the slip angle of the turn (direction of momentum).

It's all about the available traction and the balance of the car.