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Sprung vs. unsprung weight

Discussion in 'Ferrari Discussion (not model specific)' started by solly, Mar 31, 2004.

  1. solly

    solly Formula 3

    Jun 2, 2001
    1,148
    Westchester NY
    Full Name:
    Dr. Steven S.
    This may be a question more for the technical forum, if so I apologize.

    What is the issue with reduction in sprung vs. unsprung weight? Some old posts I read suggest it is better to reduce unsprung weight. Why is this so?

    Also, does unsprung weight refer to only wheels and tires, or to parts of the frame and suspension as well?
     
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  3. Dave

    Dave F1 Rookie

    Apr 15, 2001
    2,722
    Little Rock
    Full Name:
    David Jones
    Kind of reminds me of... What do you mean, African or European Swallow.
     
  4. EspritSE

    EspritSE Formula Junior

    Dec 1, 2003
    509
    Colorado
    Full Name:
    Craig
    Wheels, tires, brakes, hub, half the weight of the springs, 1/2 shocks, 1/2 axleshafts,1/2 cv's, and 1/2 suspension arms.

    Craig
     
  5. Schatten

    Schatten F1 World Champ
    Rossa Subscribed Owner

    Apr 3, 2001
    11,237
    Austin, TX
    Full Name:
    Randy
    sprung weight is the chassis itself. It could also be the battery, motor, etc.

    unsprung weight is the suspension, shocks, wheels, etc. basically anything that moves.

    if you reduce the weight of say - a wheel, that wheel can spin up faster, and also spin down faster. if you reduce the weight of an a-arm, then you also increase the turn-in ability of the car, now that it is lighter weight. in essence, you'll see a greater increase in performance by dropping rotor weight, suspension, or wheel weight itself, as opposed to dropping a few pounds from getting a smaller battery, or even a lighter seat.
     
  6. sjb509

    sjb509 Guest

    To build on what Schatten said, reducing the weight of the wheel generally also has the effect of reducing the polar moment of inertia of the wheel, which allows it to be accelerated or deccelerated (rotating) more quickly.

    By reducing unsprung weight you also reduce the inertia with respect to vertical movements of the suspension, the wheel assembly is able to track pavement irregularities better. I doubt if it is common practice on normal street cars, but for motorcycles changing to magnesium wheels, adjustment to the suspension damping and spring rates are usually required to take full advantage of the handling benefits of the reduced unsprung weight.
     
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  8. robinh

    robinh Formula Junior

    Jan 3, 2004
    622
    Cambridgeshire, Engl
    Full Name:
    Robin
    Reducing unspung weight has a real and significant effect on the handling and performance of a car pound for pound than sprung weight. It's also harder to do and yet retain the strength etc.
     
  9. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,077
    With the same amount of spring, the wheel can track more surface irregualities when the unsprung weight is lighter; and with less spring, the lighter unsprung weight will track the same road irregularity just as well.

    The traction a tire can produce is related to the amount of spring (and anti-roll bar). The less spring you can use, the more traction you have.

    The ratio of unsprung to sprung weight gives you an indication of the speed (frequency) at which the car becomes underdamped with respect to road surface irregualities.

    Ferrari uses Magnesium wheels to address the unsprung weight issues, and for road cars uses smaller brake rotors than many similar performance vehicles. Using brake rotors with aluminum 'hats' reduces the unsprung weight. Using the smallest rotors that can cope with the brake heat reduces unsprund weight. Using lighter (shaved, slicks) tires reduces unsprung weight.
     

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