THE NECESSITIES OF STEERING GEOMETRY

Ever noticed the steering wheel is misaligned when driving in a straight line or the vehicle pulls to one side?

Negative camber. 2. Wheel vertical centreline. 3. Positive camber.

If the answer is yes, this could well be the classic signs of steering geometry problems, says Autodata.
Steering geometry problems generally tend to occur with aging and wearing of components. Nevertheless, they can also be caused by impacting potholes, driving over kerbs and most certainly after the vehicle is involved in a major impact.
Steering geometry, also known as wheel alignment, is the procedure required to check and if necessary, adjust settings when they have deviated away from the manufacturers’ specifications.
However, it is also important to bear in mind, if after a steering geometry inspection there is cause for re-alignment, not all geometry values are adjustable and whenever noticeable deviations from pre-defined settings are observed, the only remedial procedure available could well be component replacement.
In a series of articles to be published in this magazine, technical experts Autodata will take a look at a few steering geometry essentials to help you in your service, maintenance and diagnostic work.

Camber angle
Camber angle is the direction the front wheel is leaning relative to the wheel’s vertical centreline and depending on the lean, the camber angle is either positive or negative.
To explain in more detail, when observed from the front of the vehicle if the top of the wheel is leaning towards the engine, this is considered as negative camber. Conversely, if the top of the wheel is leaning outwards, this denotes positive camber.
If during a steering geometry examination, the measurements are outside specified tolerances and the camber angle needs amending, look for evidence of elongated holes on the suspension strut tower, or eccentric bolts or washers securing the upper and lower control arms as a means of adjustment. In their absence, scrutiny of the suspension and steering components is essential to check for any potential damage.

Castor angle
Castor angle refers to the positioning of the steering axis centreline from the wheel vertical centreline when viewed from the side of the vehicle.
If the steering axis centreline contacts the road surface ahead of the wheel’s vertical centreline, this is said to be positive castor. Whereas, negative castor implies the steering axis centreline contacts the road surface behind the wheel’s vertical centreline.
Most modern vehicles today are designed with positive castor, this in conjunction with the other geometry angles, reduces steering effort and allows the front wheels to self-straighten after a bend is negotiated.
Yet, to avert the vehicle from wandering towards the kerbside because of the apex in present day roads, the average vehicle castor and camber angles, also called cross castor and cross camber, can sometimes be set at slightly opposed settings from left to right depending on which side of the road the vehicle is driven.
In most contemporary vehicles the castor angle is non-adjustable; nonetheless, aftermarket kits do exist that can be tailored to the suspension to permit castor angle alteration.
In the next article, which will be in a future issue, Autodata will take a look at King pin inclination (KPI) and Toe-in and toe-out.
Autodata has a dedicated Wheel Alignment module to further assist technicians with wheel alignment procedures and help provide workshops with an additional revenue stream. Within the module there is a comprehensive guide which includes information on subjects such as camber angle, ride height, tyres and adjustment procedures together with manufacturer-specific data.

For more information, visit www.autodata-group.com