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Encyclopedia > Roll center

The roll center of a vehicle is the notional point at which the cornering forces in the suspension are reacted to the vehicle body. To meet Wikipedias quality standards, this article or section may require cleanup. ...

There are two definitions of roll center. The most commonly used is the geometric (or kinematic) roll center, whereas the SAE (www.sae.org) uses a force based definition.

The location of the geometric roll center is solely dictated by the suspension geometry. The SAE definition of the force based roll center is "The point in the transverse vertical plane through any pair of wheel centers at which lateral forces may be applied to the sprung mass without producing suspension roll". Note that it is a height only, the lateral location is irrelevant. The front suspension components of a Ford Model T. Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. ...

The significance of the roll center can only be appreciated when the vehicles center of mass is also considered. If there is a difference between the position of the center of mass and the roll center a “moment arm” is created. When the vehicle experiences angular acceleration due to cornering the size of the moment arm, combined with the stiffness of the springs and roll bars (sway bars in some parts of the world) dictate how much the vehicle will roll while cornering. This has other effects too such as dynamic load transfer. It has been suggested that this article or section be merged with Center of gravity. ... Angular acceleration is the rate of change of angular velocity over time. ...

Load transfer is of critical importance for vehicle stability in vehicle such as SUV’s. Ideally in high performance applications load transfer tends to be minimised as a tyre's performance is directly affected by the amount of load that it has to transmit. In a steady state turn the final load transfer, summed across all the axles, is only related to the position of the center of mass above the ground, the track width and the lateral acceleration. SUV's must shift their center of mass lower or decrease their lateral acceleration to avoid tipping. To keep them from tipping many auto manufacturer use tyres with lower grip to reduce the vehicles cornering capacity, or the roll stiffness balance front to rear can be altered to encourage understeer or oversteer as necessary to limit the maximum lateral acceleration of the vehicle. A sport utility vehicle (SUV) or off-roader is a vehicle that combines the load-hauling and passenger-carrying capacity of a large station wagon or minivan with features designed for off-road driving. ...

The geometric roll center of the vehicle can be found by following basic geometrical procedures when the vehicle is static. However, when the vehicle rolls the roll centers migrate. It is this movement of roll centers that vehicle dynamicists seek to control and in most cases limit. The rapid movement of roll centers when the system experiences small displacements can lead to stability problems with the vehicle.

Results from FactBites:

 Roll center - Wikipedia, the free encyclopedia (443 words) The roll center of a vehicle is the notional point at which the cornering forces in the suspension are reacted to the vehicle body. The location of the geometric roll center is solely dictated by the suspension geometry. The SAE definition of the force based roll center is "The point in the transverse vertical plane through any pair of wheel centers at which lateral forces may be applied to the sprung mass without producing suspension roll".
 Sway bar - Wikipedia, the free encyclopedia (558 words) If the vertical distance between the roll center and the center of gravity is not zero, a torque (roll moment) equal to the centrifugal force times the distance between the center of gravity and the roll center will be exerted on the sprung mass, causing the body to lean towards the outside of the turn. The effect of roll couple is positive camber of the wheels on the outside of the turn, which reduces their cornering grip. Roll couple is resisted by the suspension's roll stiffness, which is a function of the spring rate of the vehicle's springs and of the anti-roll bars, if any.
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