Alignment Fundamentals, Part Two

Steering Axis Inclination (SAI)

• The inward tilt at the top of the strut.• (looking from the (looking from the

front)front)

SAI and Included angle

• Include angle =

• SAI + pos. camber

SAI and Bump steer

Zero SAI would =

Major bump steer

0 Bump Steer

• SAI line meets tire vertical CL at road surface

• Tire wear reduced

• Steering effort decreased

• Less stress on components

SAI Safety Factors

• Unequal causes serious handling problems– Torque steer– Pulling during braking– Bump steer

• If SAI is out of spec– Camber will be out of spec– Bent or damaged components

Scrub Radius

• Distance between SAI line & True Vertical CL of tire at road

• Positive scrub radius – SAI line meets road inside CL of tire

• Negative Scrub Radius – SAI line meets road outside CL of tire

Pos. Scrub Radius

Negative Scrub Radius

Commonly used on front wheel drive vehicles

Toe

• The distance between the inside front edges and the inside rear edges of the tires

• Wears tires with a feathered edge• Toe-out-on-turns – inside wheel at

sharper angle that outside

Toe In & Out

Turning Radius & Toe-Out-On-Turns