An F1 Insight to Oversteer and Understeer

For Formula One cars, balance is key to moving through a corner fast. Oversteer and understeer during a corner will cause the car to move off the racing line potentially slowing the car down or even making it crash. On the straight lines of a racing circuit, the most important factor is usually the power of the engine to gain the highest top speed possible. For corners, it is all about downforce: getting the right balance so neither oversteer or understeer occurs during the corner.


Oversteer and Understeer

During corners, there are two main forces happening to a car which are outlined through the below diagram:


The force pushing the corner away from the racing line is the centripetal force. To counteract this is the mechanical grip from the tyres. When a racing car moves through a corner smoothly, it is usually because the mechanical grip from the tyres is equal or more than the centripetal force pushing the car away from the corner. But, what determines the size of the mechanical grip?
  • The Tyre compound. If the car has more rubber touching the surface of the road, there is more mechanical grip. If the compound is also softer, it tends to flex better around corners keeping the car on the racing line.
  • Level of downforce. The rear and front wings of an F1 car work to anchor and push the car down. This means that there is a pressure being exerted on the tyres increasing the friction of them between the surface of the road and the tyres. If the friction increases, it will be harder for the tyre to slide over the road surface. Therefore, it will require a greater centripetal force to make it slide off the racing line. This means the higher the downforce, the greater grip there is. Too much downforce, though, will cause the tyres to wear much faster - there is always a balance in F1.

Oversteer 

Oversteer occurs when there is not enough mechanical grip on the rear tyres. This causes the back end of the car to swing in the direction of centripetal force and the car to slide.


There are two main ways to regain control from oversteer. Both examples involve the driver turning the wheel into the direction of the racing line so that the car is kept on the racing as much as possible even with oversteer. This also prevents the car from spinning around and the driver from losing any more control of the car.

To counteract oversteer, the driver tends to let the rear end reconnect with the road to prevent further sliding. To do this, the driver backs off from accelerating. The rear tyres will then regain grip with the road and the car can accelerate away. The problem with this is that lots of speed will be lost and the car may be off the racing line.

However, some drivers accelerate: even if the rear wheels are spinning. In this situation, the driver is ignoring the fact he has no mechanical grip on the rear tyres and is trying to maintain the speed through the corner even if the tyres are being worn out quicker.

With modern F1 cars, they use a blown diffuser which creates more downforce when the revs on the engine are high (because the exhaust fumes are pumped to the diffuser and rear wing creating higher levels of downforce). Therefore, in the event of oversteer, it is actually better for the driver to accelerate because through accelerating, the level of downforce over the rear of the car will increase from the blown diffuser. This means that, although unnatural to do so, it is better to accelerate with high revs with oversteer in an F1 car of the modern generation. Wheel spin is likely to decrease (regaining rear grip) due to the increase in downforce caused from the exhaust fumes from the high revolutions of the engine.


Understeer

Understeer occurs when there is not enough mechanical grip on the front tyres. For this reason, when the car turns into the apex, the direction the car moves in will not change causing it to run wide. In essence, the driver will turn the wheel but there is not enough mechanical grip for the car to move in the direction the driver is requesting. Instead, the front tyres slide and move in the direction of the car moved in before the corner.


Understeer is the driver's worst nightmare. With oversteer, there are two ways you can correct it with both not losing too much time. Remember that with understeer, grip is lost from the front wheels so the car cannot turn. To correct understeer, the driver most turn his car into the direction of the understeer and reconnect the front tyres to the road. This often means that the driver will be far off line and could even go off the track.