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HI,
Both Topless and John V, while spot on, are describing the means with which to over come Understeer. But the Car, as set-up by the Factory, does have an inherent understeer.
The two most important factors that influence understeer and oversteer are Weight Distribution of the car and Roll Resistance which is varyable by selective spring rates. Having a basic design influence on these factors are front and rear Roll Center locations and Center of Gravity location (the height of the CG, or CGH) .
All factors affecting the car's handling act through the tires to the road surface. The most important tire characteristic is its development of a Slip Angle when lateral force (or accelerations) are applied. All pneumatic tires deform while cornering to some degree. They will follow a path between the steered angle and straight ahead.
Slip Angle is the difference between the line the tires are steered on and the line they actually follow. Slip angle is actually a drift angle. The angle of tire slip can depend on speed, lateral acceleration, vertical load on tire, coefficient of friction of the rubber, and tire pressure.
If the outside rear tire has a larger Slip Angle than the front outside tire, the car will oversteer. If the outside front tire has larger Slip Angle than the rear tire, it will exhibit understeer.
For example, a front heavy car will oversteer because the outside tire on the front will require a larger slip angle to handle the heaveir weight loading. Increasing the roll stiffness (with stiffer spring rates) on one end of a vehicle will yield a large Slip Angle on that end of the car. If the Roll Center is raised on one end, it will increase the load transfer and thus the Slip Angle at that end of the car. Varying tire pressure will also vary the Slip Angle. Lowering tire pressure will lower the load carrying capacity of a tire, so slip angle will be increased, conversely increasing the pressure will have the opposite effect.
Happy Motoring!... Jim'99
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