Suzuki XL7 2007 Service Manual page 1029

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.
Thrust Angles 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.
If the thrust angle is not set properly the vehicle may
"dog track", the steering wheel may not be centered or it
could be perceived as a bent axle. Thrust angle can be
checked during a wheel alignment.
Positive thrust angle means the thrust line is pointing to
the right hand side (RHS) of the vehicle.
Negative thrust angle means the thrust line is pointing to
the left hand side (LHS) of the vehicle.
If the thrust angle is out of specification, moving the axle
to body relationship will change the thrust angle reading.
If the vehicle is out in the Positive (+) direction-moving
the RHS forward and/or LHS rearward will move the
thrust angle towards zero degrees.
If the vehicle is out in the Negative (−) direction-moving
the RHS rearward and/or LHS forward will move the
thrust angle towards zero degrees.
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.
NOTE
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:
• Road slope
• Variability in tire construction
• Wheel alignment (front cross caster and camber)
• Unbalanced steering gear
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.
Rear Suspension: 2C-2