Originally posted by Antiramie:
On a FWD car, when you lift the throttle the weight is distributed again to the front wheels (which your steering controls) and therefore more control is gained of the car's action.
This would be right in a leisurly driving situation, but under "performance" conditions, traction is the limiting factor. With 100% of available traction used up as cornering power under part throttle, transferring weight to the front will overwhelm the rubber's ability to turn the car.. resulting in understeer.
Consequently, taking weight off the rear tires eases their work.. making damn sure they won't slip.
A RWD car will swing the tail under those conditions not because of the weight transfer, but because of the braking force that engine compression is applying to the rear wheels alone.. essentially the same thing as putting in a click or two on the ebrake!
Dips in the road, uneven steering input, camber changes along the corner, uneven throttle input are all things that can upset the theoretical behaviour of a car tough. A conveniently located gravel patch, different asphalt texture or a pool of engine oil also make a huge difference.. turning a plowing behemoth into a tail-wagging demon under high cornering load...
