Understeer is a term for a car handling condition in which during cornering the circular path of the vehicle's motion is of a greater radius than the circle indicated by the direction its wheels are pointed. The effect is opposite to that of oversteer. In simpler words understeer is the condition in which the front tires do not follow the trajectory the driver is trying to impose while taking the corner, instead following a more straight line trajectory. Understeer covers several different phenomena, in particular, there is a big difference between linear range understeer, typically between 0 and 0.4g, and limit handling understeer, which is at higher lateral accelerations, and is what racing drivers are talking about when they use the term.
The latter is also often referred to as pushing, plowing, or refusing to turn in. The car is referred to as being "tight" because it is stable and far from wanting to spin.
As with oversteer, understeer has a variety of sources such as mechanical traction, aerodynamics and suspension.
Classically, understeer happens when the front tires have a reduction in traction during a cornering situation, thus causing the front-end of the vehicle to have less mechanical grip and become unable to follow the trajectory in the corner.
In modern race cars, especially open wheel cars, understeering is caused mainly due to the aerodynamic configuration. In this respect, the lack of a heavy aerodynamic load (downforce) in the front side prevents the front tires from gaining enough traction. At the same time understeer can be caused by having a heavier aerodynamic load at the rear end of the car giving the rear tires more traction than the front tires. Also, suspension balance should take into account the types of surfaces being driven—differing levels of friction in each surface influence the potential understeer behavior. Camber angles, ride height, tire pressure and centre of gravity are important factors that determine the understeer/oversteer handling condition.
It is common practice among automobile manufacturers to configure production cars deliberately to have a slight linear range understeer by default. If a car understeers slightly, it tends to be more stable (within the realms of a driver of average ability) if a violent change of direction occurs, improving safety. However, if the owner fits new tires to the front axle only, they will tend to reduce the understeer margin, which can cause handling problems, as claimed in San Luis Obispo County Court Case CV078853, and others. The recommendation from most manufacturers when replacing only two tires is to fit the unworn ones to the rear, and the best of the old ones to the front axle, for this reason. However, this is not ideal either.
Primarily, the cause for understeer is excessive braking, especially when cornering. While understeer isn't that common on four-wheel drive and rear-wheel driven vehicles, it still occurs on all engine layout, but having an FF layout is more common.
An error that amateur drivers tend to make is to increase the front camber, or tilt of the tire, so much that the tire no longer has all its tread on the road surface. Because of this, the tire can not attain the minimum amount of friction required to hold the vehicle to the road properly.
In higher powered front wheel drive cars, it is also easy to cause understeer. If accelerating while turning at the same time, the tires are doing too much at once. The car will begin to understeer off. A example of a car that has a tendency to understeer is a Vauxhall Astra VXR.
In Gran TurismoEdit
There are several high-powered cars that tend to understeer, such as the Nissan SKYLINE GT-R V • spec II (R32) '94, Volvo S60 T-5 Sport '03, Alfa Romeo 147 GTA '02, Acura NSX '91, and many more. This can easily be "cured" by applying a fully customizable racing suspension service.