Alignment: Description and Operation

Front and rear wheel alignment involves the correct positioning of the tire contact patch in relation to the pavement. This involves correct adjustment, or positioning, of all the interrelated suspension angles and linear distances, such as caster, camber, wheel toe, and front and rear toe pattern. An alignment is considered essential for efficient steering, good directional stability, and to prevent abnormal tire wear.

NOTE: Routine inspection of front and rear suspension, and steering components, is a good preventative maintenance practice. Inspection also helps to ensure safe operation of the vehicle.

The method of measuring front and rear wheel alignment will vary depending on the type of alignment equipment being used. The instructions provided by the manufacturer of the equipment should always be followed. The exception to this is the alignment specifications which should always have precedence.
There are 7 suspension system and steering linkage measurements that are used to determine if the front and rear wheel alignment is correct.
All suspension angles and linear distances are mechanically adjustable, except steering axis inclination and wheel toe out on turns. Although not adjustable, these measurements are valuable in determining if there are bent or damaged components involved.

NOTE: The Viper suspension geometry is such that the vehicle suspension and alignment settings change rapidly as the vehicle changes height. For this reason, it is extremely important that all suspension specifications be checked and adjusted with the vehicle at the correct height. Alignment specifications are required to be checked with a vehicle at curb height, the fuel tank must be full, fluids at the correct fill level, and all factory supplied equipment (top, removable windows, spare tire etc.) must be in the vehicle. No passengers or additional weight should be added to the vehicle. This will put the vehicle at the correct weight which its curb height is to be measured at. When checking vehicle design height, ballast must be added and/or vehicle must be jacked to specified design height before design height can be measured, To check either vehicle curb height, or design height, height checking fixtures must be used.

NOTE: The front and rear vehicle curb height must be measured and adjusted before any other alignment measurement/adjustment is initiated.

The measurements and adjustments should be made in the following sequence.

CAUTION: Do not attempt to modify any suspension or steering component by heating and bending.

VEHICLE FRONT AND REAR CURB HEIGHT
Vehicle front and rear curb height is the difference in height between the outer end of front and rear lower control arms and the frame of the vehicle. The measurement is to be taken from the design height fixture to the vehicle's frame, to determine the height of a fully wet (full tank of fuel and all correct fluid levels) vehicle. This measurement will determine if something in the vehicle's suspension is causing a vehicle to sit statically high or low. The curb height measurement is taken at the center in the front of the vehicle, and at each frame rail in the rear. All service alignment adjustments done on this model year Viper MUST be made with the vehicle set to its required curb height specification.

VEHICLE DESIGN HEIGHT
Vehicle design height is the height specification vehicle was at, when vehicles original front and rear alignment was done at the vehicle assembly plant. This is also the height specification vehicle was at when all suspension components were originally tightened and torqued to required specifications. It is also the height specification vehicle MUST be at when tightening and torquing fasteners for the vehicles suspension components which are mounted, using rubber isolator bushings. This is required for all vehicle suspension components, except for the front, and rear, lower control arm cam bolts and nuts, since they are used to adjust camber and caster which is set at curb height. Vehicle design height is determined by correctly installing the front and rear design height fixtures and then ballasting or jacking the vehicle until the required vehicle is obtained using the vehicle height fixture special tools.

CAMBER
Camber is the number of degrees the top of the wheel is tilted either inward or outward. An excessive negative camber angle will cause tread wear at the inside of the tire. An excessive positive camber angle will cause tread wear at the outside of the tire.

CASTER
Caster is the number of degrees of forward or rearward tilt of the steering knuckles. Forward tilt provides a negative caster angle. Rearward tilt provides a positive caster angle. Positive caster angle promotes directional stability. This angle enables the front wheels to more easily return to the straight ahead position after turns.

WHEEL TOE POSITION
Wheel toe position is the difference between the leading inside edges and trailing inside edges of the tires. Incorrect wheel toe position is the most common cause of unstable steering and uneven tire wear. The wheel toe position is the final front and rear wheel alignment adjustment.

FRONT AND REAR WHEEL TOE PATTERN
Front and rear wheel toe pattern is the inward and outward movement of the front and rear tires through jounce and rebound of a vehicles suspension. Toe pattern is critical in controlling the directional stability of a vehicle, as its suspension moves through its normal jounce and rebound travel. Front and rear wheel toe pattern is set by the factory at the time the vehicle is aligned. It is not necessary to check or adjust front or rear wheel toe pattern when doing a vehicle alignment. The only time wheel toe pattern needs to be checked or adjusted is if the frame of the vehicle has been damaged.

STEERING AXIS INCLINATION ANGLE

Wheel Alignment Measurements:

Steering axis inclination angle is measured in degrees and is the angle that the knuckles are tilted. The inclination angle has a fixed relationship with the camber angle and will not change, except when a spindle or ball stud is damaged or bent. The angle is not adjustable and the damaged component(s) must be replaced to correct misalignment.