THE NECESSITIES OF STEERING GEOMETRY

In this second article of a two part series, Autodata looks at King Pin Inclination and Toe-in and Toe-out

Autodata has a dedicated Wheel Alignment module to 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.
After looking at Camber Angle and Castor Angle in the last issue of this magazine, this issue Autodata explores two other common wheel alignment issues: King Pin Inclination and Toe-in/Toe-out.

1. King Pin Inclination

King Pin Inclination (KPI)
King pin inclination (KPI), also called steering axle inclination (SAI), is achieved differently depending on the suspension arrangement. Typically, with the MacPherson strut type suspension, KPI is attained by leaning the strut. While with the control arm type suspension, the angle of the upper and lower swivel joint pivots is offset.
KPI, being non-adjustable, can often be left unchecked or overlooked in collision situations. Incorrect KPI caused by worn or damaged suspension components usually results in accelerated tyre wear along with poor directional stability and increased steering effort – particularly when the vehicle is implementing a parking manoeuvre.

1. Toe-in. 2. Vehicle centreline. 3. Toe-out.

Toe-in and Toe-out
Toe-in and Toe-out, commonly referred to in automotive terms as tracking, is the most frequent steering geometry adjustment undertaken.
This is the degree to which the leading edge of the front wheels steer out or in from the vehicle centreline when observed from the front. A situation where the wheels are pointing in towards the vehicle centreline is called Toe-in whereas wheels pointing away from the vehicle centreline is identified as Toe-out.
Making sure the vehicle’s Toe-in or Toe-out measurement is correct offers many advantages, including improved straight-line stability, better road handling characteristics and more effective steering response.
Should it be necessary, this adjustment will also allow minor tweaks to correct suspension bush disparities caused in production or by accepted wear levels.
If adjustment is needed, it is worthwhile remembering to adjust the track rods equally. Although, there is one notable exception to the rule which requires the repositioning of a misaligned steering wheel by minutely adjusting one track rod more than the other.
Guaranteeing precise steering geometry alignment is vital in prolonging the life of tyres and ensuring vehicle stability. Regular steering geometry checks are advisable, and not only when changing worn tyres, steering or suspension components.
Checks should also be carried out if subframe removal is required to facilitate gearbox or clutch repair work.
Finally, it must be pointed out that rear wheel geometry can influence steering stability as well. It is possible to have the front steering geometry angles correctly aligned and still have a vehicle that pulls to one side or displays abnormal tyre wear patterns.
In such circumstances, it is imperative rear wheel geometry is also considered when confronted with a vehicle experiencing unusual tyre wear or stability issues.

To read the first part of the article visit www.aftermarket.com.au/the-necessities-of-steering-geometry/
For more information, visit www.autodata-group.com