Alignment Fundamentals, Part Two

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Alignment Fundamentals, Part Two
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Steering Axis Inclination (SAI)

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

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SAI and Included angle

• Include angle
• SAI pos. camber

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SAI and Bump steer
Zero SAI would Major bump steer
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0 Bump Steer

• SAI line meets tire vertical CL at road surface
• Tire wear reduced
• Steering effort decreased
• Less stress on components

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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

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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

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Pos. Scrub Radius
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Negative Scrub Radius
Commonly used on front wheel drive vehicles
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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

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Toe In Out
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Turning Radius Toe-Out-On-Turns