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8 July 2024 Understeer and oversteer: what they are, differences, and causes
Understeer and oversteer are terms used to describe how a car handles when it's cornering and loses grip. They basically refer to which end of the car slips out first, the front or the rear.
It's generally considered safer to have a car that understeers because it's more predictable and easier to correct. That's why most cars are designed this way. However, some performance drivers may use controlled oversteer to manoeuvre quickly through tight corners. This is a risky technique and should only be attempted by professionals on a closed track.
What is understeer: meaning and explanation
This is when the front wheels lose traction and don't turn enough, causing the car to go straighter than you intended, as if pushing to the outside of the corner. Understeer is more common in front-wheel drive cars because the front wheels are doing double duty, steering and providing power.
Drivers can use several techniques to reduce understeer, including adjusting speed before cornering, modulating throttle and brake inputs smoothly, and optimising steering technique to maintain control and maximise traction.
What causes understeer?
Understeer is a consequence of the driver's actions directly influencing the vehicle's behaviour. It typically occurs when the driver applies excessive or abrupt steering input that exceeds the available traction of the front car tyres relative to the vehicle's speed. This imbalance causes the front of the car to lose grip and veer wide, sliding across the road surface in an understeering motion. Essentially, understeer occurs when the steering commands exceed the tyres’ grip, resulting in a lack of responsiveness and loss of control, most notably when the vehicle fails to follow the intended path through a corner.
Additionally, a stiffer car anti-roll bar in the front compared to the rear can also contribute to understeer by limiting weight transfer to the front outside wheel during cornering, reducing its grip.
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What is Oversteer: meaning and explanation
Oversteer is a driving phenomenon characterised by the rear wheels losing traction and sliding outwards, causing the rear of the car to swing outwards, similar to a fishtail. This dynamic often occurs when the force applied to the rear wheels exceeds their available grip, leading to a loss of control of the vehicle's path, particularly when cornering or changing direction suddenly. This can be caused by aggressive use of the accelerator pedal out of a bend, suddenly releasing the throttle mid-bend, or entering a bend too quickly.
What causes oversteer?
Oversteering occurs when the driver enters a bend or corner at a speed that exceeds the car's handling capabilities. This excessive speed causes the rear wheels to rotate faster than the front wheels, disrupting the vehicle's dynamic balance.
As a result, the rear of the vehicle tends to swing outwards, potentially out of the driver's control and compromising stability. Essentially, it is the discrepancy between the rotational speeds of the front and rear wheels, resulting in a loss of control over the vehicle's path, particularly during high-speed manoeuvres or abrupt steering inputs. Adjusting throttle and steering inputs to regain traction and stabilise the vehicle's dynamics is one of the techniques used to reduce oversteer.
Understeer vs Oversteer: differences explained
Two key terms define how a car loses traction when cornering: understeer and oversteer. Understeer is when the front wheels lose grip, causing the car to oversteer or go straighter than intended. Imagine the car stubbornly refusing to turn enough, as if it's understeering to the outside of the corner. This typically happens when you enter a corner too quickly or make abrupt steering movements.
Conversely, it occurs when traction is lost by the rear wheels, causing the rear end to swing out like a fishtail. This can lead to a spin if not carefully controlled. It is more common in rear-wheel drive cars and can be caused by sharp manoeuvres or taking a corner with too much power. If you know the difference between understeer and oversteer, you can anticipate potential problems and react accordingly to maintain control when cornering.
To find out more about cornering control, take a look at CSC: definition, function, operating principle, and causes of failure.
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