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Introduction What is an Automotive Suspension?
An Automotive Suspension is the system of parts that give a vehicle the ability to maneuver.
It is a 3 Dimensional Four Bar Linkage
What does a suspension do?“The job of a car suspension is to maximize the
friction between the tires and the road surface, to provide steering stability with good handling” HowStuffWorks.com
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Ride Height, Bump & Droop
Ride Height The neutral /
middle position of the Suspension
Bump When the wheel
moves upwards Droop
When the wheel moves downwards
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Camber Tires generate
more cornering force with a small amount of negative camber
Camber changes as suspension moves up (bump) and down (droop)
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Caster Shopping cart
action Causes self-
centering action in the steering
More caster results in more camber as front wheels are turned
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Toe-in or Toe-out Toe-in results is
inherently stable Toe-out is
inherently unstable
Race cars often use front toe-out, & rear toe-in
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Beam Axle Around since horse
and chariot days Always keeps
wheels parallel Often used in rear Rarely used in front OK on smooth
tracks
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Swing Axle Often used on VW
based off road cars Simple and rugged Camber curve too
steep Only adjustment
you can make is ride height
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De Dion Essentially a
beam axle with the diff now sprung weight
Keeps wheels parallel
Relatively light weight
Better on smooth tracks
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Basic Vehicle DynamicsPart 2
What is Vehicle Dynamics?
The understanding and study of how a vehicle and its components move and react
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Yaw, Pitch, and Roll Same terminology
as aircraft X is the
longitudinal axis Yawing refers to
normal change of direction
Pitching is dive or squat
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Understeer Front end of the car
“washes out” or doesn’t “turn in”
NASCAR boys call it “push” or “tight”
Safe, because lifting off throttle reduces it
Most road cars have a ton of it
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Oversteer Rear end of car slides out NASCAR boys call it
“loose” Excessive application of
power can cause oversteer Throttle induced oversteer
is never the fast way around a corner
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Weight Transfer Occurs anything the
vehicle accelerates or decelerates
Cornering force Fc will cause weight to transfer from the inside to outside tires
Braking and accelerating forces cause a similar front and rear weight transfer
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Roll Center A geometric construct Represents the instantaneous
point about which the sprung mass will rotate due to cornering forces
Roll center moves as suspension travels
Goal of any suspension designer is to minimize Roll Center Migration
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Roll Couple Distance from roll
center to CG is key Low roll center results
in more roll for a given lateral acceleration
Most designs use a low roll center to reduce jacking forces
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Anti-dive Purely geometric
method to reduce pitch movement
Reduces suspension compliance over bumps
No longer in favor with formula car and sports racers
Might work well for Baja
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Bump Steer Caused when toe
changes as suspension moves up and down
Causes car to react unexpectedly over bumps and in roll
Sometimes used intentionally, but be careful
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Tire Slip Angle Angle between
the centerline of the wheel and the actual path
Tires generate highest cornering forces at a certain slip angle
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Slip Angle vs. Grip Grip is highest a set
angle, then falls off as the slip angle increases
Sharper peak will give a less predictable breakaway
Radial tires typically have a steeper slope than bias ply
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Friction Circle Plots the
theoretical limits of adhesion in 2 axes
Great tool for analyzing driver to driver variation
G-analyst is a cheap tool for this
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Friction Circle, cont. Illustrates the trade off
between cornering and braking/accelerating
The driver that follows the path closest to the outside of the circle wins