Alignment Fundamentals, Part Two
Steering Axis Inclination (SAI) The inward tilt at the top of the strut. (looking from the front)
SAI and Included angle Include angle = SAI + pos. camber
Zero SAI would = Major bump steer 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