Escalade V8-5.7L VIN R (2000)
Toe is a measurement of how much the front and/or rear wheels are turned in or out from a straight-ahead position. When the wheels are turned in, toe
is positive (+). When the wheels are turned out, toe is negative (-). The actual amount of toe is normally only a fraction of a degree. The purpose of toe
is to ensure that the wheels roll parallel.
Toe also serves to offset the small deflections of the wheel support system that occur when the vehicle is rolling forward. In other words, with the
vehicle standing still and the wheels set with toe-in, the wheels tend to roll parallel on the road when the vehicle is moving. Improper toe adjustment
will cause premature tire wear and cause steering instability.
Thrust Angle Description
The front wheels aim or steer the vehicle. The rear wheels control tracking. This tracking action relates to the thrust angle (3). The thrust angle is the
path that the rear wheels take. Ideally, the thrust angle is geometrically aligned with the body centerline (2). In the illustration, toe-in is shown on the
left rear wheel, moving the thrust line (1) off center. The resulting deviation from the centerline is the thrust angle.
Lead/Pull Description
Lead/Pull is the deviation of the vehicle from a straight path, on a level road, without hand pressure on the steering wheel. Lead/Pull is usually caused
by the following:
-
Tire construction
-
Uneven brake adjustment
-
Wheel alignment
The way in which a tire is built may produce lead/Pull. The rear tires will not cause lead.
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.
Setback Description
Setback applies to both the front and the rear wheels. Setback is the amount that one wheel may be aligned behind the other wheel. Setback may be the
result of a road hazard or a collision. The first clue is a caster difference from side-to-side of more than 1 degree.
