Lift-off oversteer

Lift-off oversteer (also known as snap-oversteer, trailing-throttle oversteer, throttle off oversteer, or lift-throttle oversteer) is a form of oversteer in an automobile that occurs when the vertical load on the tires shifts from the rear to the front quickly due to throttle release while cornering. This decrease in vertical load causes a decrease in the lateral force generated by the rear axle, so the axle starts to accelerate towards the outside of the turn. This steers the car more tightly into the turn, hence causing oversteer. In essence, this means that easing off the gas causes the rear wheels to break away suddenly, with the potential for the car to leave the road tail first.

Causes and countermeasures

This type of oversteer is often more pronounced in rear-engined cars and cars with swing axle rear suspension. Rearward centers of gravity (such as older Porsche 911s) enhance this effect, though technically any vehicle can experience lift-off oversteer. Various suspension enhancements, such as a Weissach axle, Passive rear wheel steering, or a multi-link suspension, can limit a vehicle's tendency to oversteer in this situation. Even the handling of the Chevrolet Corvair improved in final years of production through the use of enhanced anti-roll bars, according to John DeLorean's book, "On a Clear Day You Can See General Motors".

cientific analysis

The graphs to the right show the effect of lifting off the throttle mid turn, at 6s. The transients in the first couple of seconds are due to the test, which applies the steering lock at 0s, which is effectively a step steer input. The steering wheel is held at a constant angle throughout. The steady state cornering is at constant speed, with a lateral acceleration of 0.45 g approximately. After the throttle is released the lateral acceleration spikes to 0.6g, and then smooths out to about 0.54g. The yaw rate plot is more interesting - the spike to 20 deg/s is significant as that would be quite uncomfortable. Note that the inside rear wheel lifts off the ground, this is quite common.

In popular culture

In the 1940's, the Nazis described the Tatra automobile as the "Czech Secret Weapon" due to its treacherous and deadly lift-off oversteer handing characteristics.

The famous American attorney Ralph Nader described this type of handling in his 1965 book "Unsafe at Any Speed".

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