9-7X V8-6.0L (2008)
Caster Description
Caster is the tilting of the uppermost point of the steering axis either forward or backward, when viewed from the side of the vehicle. A backward tilt is
positive (+) and a forward tilt is negative (-). Caster influences directional control of the steering but does not affect the tire wear. Caster is affected by
the vehicle height, therefore it is important to keep the body at its designed height. Overloading the vehicle or a weak or sagging rear spring will affect
caster. When the rear of the vehicle is lower than its designated trim height, the front suspension moves to a more positive caster. If the rear of the
vehicle is higher than its designated trim height, the front suspension moves to a less positive caster.
With too little positive caster, steering may be touchy at high speed and wheel returnability may be diminished when coming out of a turn. If one wheel
has more positive caster than the other, that wheel will pull toward the center of the vehicle. This condition will cause the vehicle to pull or lead to the
side with the least amount of positive caster.
Lead/Pull Description
Lead/Pull Description
At a constant highway speed on a typical straight road, lead/pull is the amount of effort required at the steering wheel to maintain the vehicle's straight
path.
Important: Vehicles will tend to lead/pull in the direction of the road slope as part of normal operation.
Lead/pull is usually caused by the following factors:
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Road slope
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Variability in tire construction
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Wheel alignment (front cross caster and camber)
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Unbalanced steering gear
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Electronic Power Steering (EPS) steering position and torque sensors not calibrated correctly, if equipped.
Scrub Radius Description
Scrub Radius Description
Ideally, the scrub radius is as small as possible. Normally, the SAI angle and the centerline of the tire and the wheel intersect below the road surface,
causing a positive scrub radius. With struts, the SAI angle is much larger than the long arm/short arm type of suspension. This allows the SAI angle to
intersect the camber angle above the road surface, forming a negative scrub radius. The smaller the scrub radius, the better the directional stability.
Installing aftermarket wheels that have additional offset will dramatically increase the scrub radius. The newly installed wheels may cause the centerline
of the tires to move further away from the spindle. This will increase the scrub radius.
A large amount of scrub radius can cause severe shimmy after hitting a bump. Four-wheel drive vehicles with large tires use a steering damper to
compensate for an increased scrub radius. Scrub radius is not directly measurable by the conventional methods. Scrub radius is projected geometrically
by engineers during the design phase of the suspension.
Wander Description
Wander Description
Wander is the undesired drifting or deviation of a vehicle to either side from a straight path with hand pressure on the steering wheel. Wander is a
symptom of the vehicle's sensitivity to external disturbances, such as road crown and crosswind, and accentuated by poor on-center steering feel.
