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Understanding Oversteer.

Oversteer: the car makes the turn too sharp and gets into a spin.
Auto Gearhead: In previous article we have talk about understeer, in  this articel we gonna talk more about understeer. Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Simply put, oversteer is what occurs when a car turns (steers) by more than (over) the amount commanded by the driver. Automotive engineers define understeer and oversteer based on changes in steering angle associated with changes in lateral acceleration over a sequence of steady-state circular turning tests.



An article from drivingfast.net says, when you reach the limits of grip on a corner, two scenarios can result known as understeer or oversteer. Oversteer, like understeer, results from the car reaching the limits of traction on a corner. In this case, the rear tyres reach the limit of adhesion before the front. This leads to 'the back coming out'. The good thing about oversteer is that you normally go through the hedge backwards, thus preventing expensive repairs to the front of your vehicle. If you manage to performed sustained, controlled oversteer this is know as drifting.

Symptoms of oversteer It's unlikely you'll ever experience oversteer unless you're driving a car near the limits of grip. You can recognise oversteer if, the rear of the vehicle becomes unstable and 'light' due to lack of grip and the car starts to rotate so the driver is facing towards the inside of the corner

There are four major active causes of oversteer, but what you're likely to encounter depends on the car being driven, causes include:
  1. Entering the corner too fast.
  2. Accelerating into the corner, too early or too aggressively.
  3. Braking into the corner or mid corner.
  4. Lifting off the throttle mid-corner. This scenario is also known as:
  • lift-off oversteer
  • snap-oversteer
  • trailing-throttle oversteer
  • throttle off oversteer
  • lift-throttle oversteer
  • lift-off oversteer
Lift-off oversteer is a phenomenon which can occur when reducing the throttle mid corner. This will only happen when driving close to the limit so only experiment when on the track. Sporty front wheel drive drive cars can be especially prone to this due to the heavy front end and light rear. Reducing the throttle input results in a forward weight transfer, which increases the grip at the front tyres, but reduces levels at the rear. If this is performed during cornering, the combination of the heavy front end and the reduction of grip can cause the rear wheels to break traction and start to slide towards the outside of the corner.

Whatever the cause of oversteer it is important to keep the front wheels pointing in the direction you're hoping to go. If you fail to do this, the most likely result is a spin. This technique is known as counter-steering or applying opposite lock. You should apply enough steering lock to point the wheels in the direction of the slide as shown below. Too little and you're likely to spin as the back continues to come round, too much and the car will rapidly over-correct, often resulting in a spin in the opposite direction. The skill can only be mastered with plenty of practice and should become instinct if you're planning to drive fast on a track.

Applying corrective steering needs to be done rapidly to catch the back of the car before it slides to a point which may be difficult to control. Once the slide has been controlled and the back starts to fall back in line, it's also important to get the steering correction off quickly too, otherwise you might find your self with oversteer in the opposite direction due to the resulting pendulum effect.(*)



A video with Martin Brundle describing Oversteer and Understeer.

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