How to Calculate Torsion Bar Rates

Written by lee lyons
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How to Calculate Torsion Bar Rates
You'll find torsion bars on most off-road vehicles. (Jupiterimages/Pixland/Getty Images)

Torsion bars function as springs in off-road vehicles and some sprint cars. They are connected to the base of the vehicle, and then to a pivot that allows the vehicle to hit a hard bump without damaging the suspension. Torsion bars can be hollow or solid. Which one you use should be determined by track conditions and the type of tires you have on your car. To calculate a torsion bar rate, you simply calculate the amount of spring the bar can withstand.

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Things you need

  • Tape measure
  • Ruler

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    Hollow Bars

  1. 1

    Subtract the interior diameter to the fourth power from the outside diameter to the fourth power.

  2. 2

    Multiply that remainder by the torsional resistance. In the case of hollow torsion bars, that should be 1,129,000.

  3. 3

    Multiply the torsion arm's length squared by the bar's length itself.

  4. 4

    Divide the product of the torsional resistance and the diameters by the product of the arm and bar's length.

    Solid Bars

  1. 1

    Multiply the torsional resistance by the torsion bar's diameter to the fourth power. Since this is a solid bar, there is no need to figure the interior diameter. The torsional resistance for solid bars is 1,120,000.

  2. 2

    Multiply the torsion bar length by the torsion arm's length squared.

  3. 3

    Divide the product of the resistance and the diameter by the product of the bar and arm's length.

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