In technical terms, over-steer means that rear tyres of a car are functioning at a greater slip angle or harder as compared to the front wheels. The actual scenario in this situation is tail of the car that’s sliding sideways and holding the vehicle in the dynamic state results in incredible drift.
However, if you fail holding or balancing the car, it’ll end up spinning out of control. This is all the game of car tyre and to control over-steering in rear drive is about separate regulation of the lateral velocity at each end. Here’s what’s likely to happen when your car goes sideways.
A spinning car tyre has less lateral and longitudinal grip than a rolling one. When there isn’t any effective traction in the rear wheels due to spinning, tail of the vehicle usually slide towards the outside but they do offer some gripping. What’s more important is that the tyres still produce ample forward thrust so the tail always slides at an angle with respect to the direction of vehicle’s movement.
The real challenge is for the driver to keep the front wheels ahead of the rear and since traction is inversely related to the rotational speed of the rear tyre, they may give up smoke while removing the traction feature. This however happens when driver flat-foots the vehicle! Reducing the power would eventually let the rear wheels slow down, increases lateral bite whereas reduces lateral velocity.
At up-front position, the tires are planted and to prevent spinning, driver steers in the slide direction. This is known as counter-steering or “turning into the slide” as it allow front of the vehicle to move in lateral direction. On straightening the tyres, lateral velocity of the rear wheels is reduced which causes the tail to rotate swiftly. If driver steers more, the result is totally opposite which factors in limiting the over-steer control due to finite amount of steer lock mechanism.
Over-steer: How to induce & do it right?
Encouraging over-steer means you’re overloading the rear tyres. Power-side is most common in rear-drive over-steering but most cars lack the feature to tackle it properly. Car tyre grip is influenced by the total load which exerts pressure on the wheel against the pavement. When a car accelerates, the tip is raised whereas the tail squats. Load of the front wheels is then transferred to the rear tyres which increases the grip on the back; which means the car is under-steered.
With more power, a car can break the grip of rear tyres but most do so in lower gear. If you add negative inclination which is tilting top of the car tyre inwards, it also increases the front grip means that a driver will soon run short of rear grip.
Increasing stiffness to the rear suspension would also raise the load transfer between in and outside of the rear tyres thereby reducing the total grip available at rear axle. In this situation, over-steering is far easier.
To know the physics and technicalities of the wheels is important to overall driving so do understand the impact of over-steering on car tyres and driving.