Skills and Knowledge
Understeer and Oversteer
Understeer and oversteer are two ubiquitous terms in the racing world used to describe car cornering behavior. It might be tough to intuitively figure out what they mean, but they are simple concepts that can help improve your driving and understanding of car control.
Understeering happens when you turn your steering wheel, but your front wheels lose traction. This results in the car not turning as intended and continuing to go relatively straight.
This usually happens when you try to turn sharply while going too fast, and your forward inertia overpowers your steering input. On the racetrack, when you enter a turn too fast and end up going wide and missing the apex, you probably understeered.
FWD cars tend to exhibit understeer more because they rely on the front wheels to do everything - turn, accelerate, and brake. This increases the overall load on your front tires, leaving less traction for turning and increasing the chances of understeer.
Simply, understeer means that your car does not turn as much as you intend it to.
If understeer means your car does not turn as much as you want, then oversteer means your car turns more than you want.
RWD cars are associated with oversteer, which is often caused by accelerating too hard while turning, causing the rear wheels to lose traction and slide out. Oversteer is not always unintentional and can be used as a technique for car control. In fact, there's a class of racing that's based entirely around oversteer. That’s right, drifting!
Another type of oversteer is snap oversteer, which happens when you're giving your car throttle mid-corner and then suddenly lift off throttle entirely. This causes all the weight of the car to shift from the rear to the front, making the rear go light and prone to sliding out. Mid-engine, rear-wheel drive cars are often suspect to this, with a common culprit being the Toyota MR2.
Grip refers to the level of friction between your tires and the road surface. If you have a lot of grip, your car will go where you steer. If you have low grip, your tires may start sliding along the road surface causing understeer or oversteer.
You can think of grip as a gauge that goes to 100%. Accelerating, braking, and turning all use up that gauge. If you're turning using 20% of your grip, then you can only accelerate/brake with 80% grip.
A good example is when you leave a turn on the track, you slowly unwind the steering wheel while increasing throttle. This is because you want turning and accelerating together to use exactly 100% of the grip level and not more. As you straighten out, less grip is required to keep you on the racing line, so you can afford to accelerate harder. However, if you add too much throttle too quickly, the combined grip usage will exceed 100%, and you'll lose traction. On the other hand, if you add too little throttle, you'll leave time on the table.
Understeer and oversteer happens when you ask your car to do more than it's capable of at its current level of grip. Sometimes this is intentional (more often it's not), but understanding how much grip is available for you to use is critical to learning how to drive your car at the limit.
How to correct understeer and oversteer
Raise front tire pressure
Lower front tire pressure
Lower rear tire pressure
Raise rear tire pressure
You may be entering the corner too fast, which forces you to turn hard and break traction in the front
You may be getting on throttle too early in the turn, which will break the rear of the car loose
Leverage trail braking to shift weight forward over the front tires
Counter-steer to straighten the car out, but you have to be careful not to overcorrect
Lift off throttle slightly or add some brake pressure to shift weight forward
In rear-biased cars, like Porsche 911s, you can add some throttle to shift weight back and help your rear wheels regain traction
Reduce steering input slightly to increase your front wheels’ contact patch with the ground