Oversteer and understeer are terms that describe how a car deviates from the driver’s intended steering angle while turning. Both happen due to loss of traction, but for different reasons.
Understeer and oversteer are typically used to talk about how a car handles corners on the race track. But they can have an effect on everyday driving too, especially in poor conditions. It’s important to know the difference between oversteer and understeer, what causes them, and how to react to stay safe.
What Is Understeer?
Understeer occurs when a car turns less than the amount that is inputted by the driver. Most common in FWD vehicles, it’s caused by the front wheels losing traction. The front-end slip angle becomes higher than the rear-end slip angle. Instead of traveling along the appropriate cornering line, understeer will send you too far towards the outside of the curve. This is extremely dangerous, as it can result in a head-on collision with opposing traffic or crashing off the roadway.
Understeer can also occur in FWD-biased AWD vehicles (which most AWD platforms are). However, this is less common, as modern AWD systems are usually intelligent enough to mitigate understeer.
What Causes Understeer?
Understeer is caused by one of several factors. While braking during a corner or bad weather can cause understeer, speed is usually the culprit.
Accelerating Too Hard Into a Corner
If you take a corner too hard, you’ll find that a FWD car can’t get enough traction to the front wheels to turn adequately. Despite aggressive steering wheel input, the wheels themselves won’t be able to rotate the vehicle, causing understeer.
Braking Too Hard
Braking too much after you’re already in a corner can upset the balance of the car. With FWD, this means too much weight over the front wheels. If they slip, there will be a loss of traction, causing understeer.
Poor Driving Conditions
Poor weather or slippery driving conditions can cause a loss of traction. Since the front wheels are the ones being driven, they need the most traction. If they can’t get a good grip on the road surface, they can fail to turn the car sufficiently, leading to understeer.
How Do You Correct Understeer?
Understeer can be corrected by counter-steering the opposite way to lessen your turn angle. You should also ease off the throttle to avoid upsetting the weight balance of the vehicle. This will help you regain traction. Use gentle actions and don’t slam on the gas or brakes.
To prevent understeer from occurring in the first place, take corners at slower speeds. Use caution in poor weather.
What Is Oversteer?
Oversteer occurs when a car turns more than inputted by the driver. It’s most common in RWD vehicles and occurs because the rear tires have lost traction. This happens when the rear-end slip angle is higher than the front-end slip angle. In an oversteer situation, the car fails to stay on the appropriate cornering line as the rear end rotates around. This is often called “fishtailing.” With a lack of traction, the car becomes unbalanced and much more difficult to control. Trying and failing to correct oversteer can be just as dangerous as oversteer itself.
It is possible to induce oversteer in a FWD car, like the Focus ST, due to corrective brake torque vectoring. However, this is much less common.
RWD cars with big engines, like the Mustang, have a tendency to oversteer when pushed hard. Pickup trucks do as well, because they have much less weight over the rear wheels.
What Causes Oversteer?
There are several potential causes of oversteer. As with understeer, bad weather or shifting the car’s balance mid-turn can be issues, but it’s usually due to speed.
Accelerating Too Early or Too Much
Hitting the gas too early while going into a corner can be risky in a RWD car. So can applying too much throttle at any time. If the rear tires receive too much power, they’ll lose grip, causing the car to oversteer.
Not Enough Weight Over Rear Tires
Not having enough weight over the rear tires can cause a lack of traction, creating oversteer. Without enough grip, the back end will rotate around. Pickup trucks with empty beds are also prone to this, especially if they’re RWD.
Adding more weight to a vehicle is usually regarded as a bad thing. However, putting some sandbags in the trunk or bed can help RWD vehicles maintain traction in poor conditions.
Lifting Off the Throttle (Lift-Off Oversteer)
Lift-off oversteer, or “snap oversteer,” occurs when a driver lets off the throttle too much while cornering. Doing so suddenly disrupts the weight balance of the car. In some vehicles, this is enough to cause a loss of traction. This can affect RWD, FWD, and AWD cars.
Poor Driving Conditions
Snow, ice, or simply a wet road can cause traction problems for RWD cars. With less weight over the driven wheels, slippage can occur more easily on a slick surface. As the rear of the vehicle follows its path of momentum, it can cause the back end to slide out.
How Do You Correct Oversteer?
Oversteer can be corrected by a change in steering input. The best advice is to look where you want to go and steer in that direction. Don’t slam on the gas or brakes, but don’t abruptly let off them either. Keep the throttle steady. Letting off the throttle or slamming the brakes while oversteering can shift the weight of the car forward suddenly. This quick shift in balance will usually make oversteer even worse.
If you’ve had enough practice on the track, you can purposely induce oversteer (drifting) to go around corners. Modulating the throttle and powering through is a legitimate driving technique. However, this is only for the track and should never be practiced on public roads.
Like understeer, you can avoid oversteer by slowing down to an appropriate speed before driving through the corner.
Oversteer vs Understeer Infographic
Check out the full infographic below for a quick recap of the information above. It covers the differences between oversteer and understeer, as well as what to do if they happen to you.
[click the infographic below]
Sources: Car Throttle | Autoweek