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Goal: Understand the higher level functionality and purpose of suspension in a race vehicle

Notes from: Race Car Vehicle Dynamics

  • There is no single best geometry, it depends on the rest of the characteristics of the car

  • An independent suspension (suspension that allows each wheel to move independently of one another when subjected to an external load) is intended to control the wheel motion relative to the body of the car in only one path (up and down)

  • The study of independent suspension geometries is to determine how to restrain the knuckle to limited motion in five directions.

  • 5 degrees of restraint (DOR) requires 5 tension-compression links

    • A-Arm = 2 links

    • McPherson strut = 2 links

  • Solid axle (or beam axle) requires 2 degrees of freedom (up/down and roll) → 4 DOR

  • Instant center (IC) - the projected imaginary pivot point of all the linkages at a specific position of the linkage

  • Instant axis - the front view and side view instant centers connected by an axis

    • Independent suspensions have 2 instant center and 1 instant axis

    • Solid axles have 2 instant axes

Suspension Geometries

Camber Angles:

  • The goal is to maximize the grip by keeping the tire orientated perpendicular to the ground

  • Lateral tire scrub is increased when you try to optimize camber angles

    • Wears tires

      For Solar cars, minimizing lateral scrub is arguably more important than optimizing camber for efficiency reasons

      Cornering isn't as important for solar cars at the speed they are travelling at

Caster Angles:

  • Positive Caster helps the car to travel in a straight line if the driver takes hands off of the wheel

    Adding caster also increases tire scrub

Toe Angle:

  • Most efficient is zero toe

    Some toe can help improve stability of the vehicle at the cost of increased tire scrub

Scrub Radius:

  • True zero scrub radius is most efficient but can result in less stable steering feel

  • Rear wheel drive

    • Positive scrub radius in the rear suspension can help improve straight line tracking

  • On front

    • Slightly, negative scrub radius can help with maintaining stability in scenarios like sudden tire deflation or hitting standing water

 

 

 

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