Front Suspension Calculations & Goals

As a base point, in order to calculate the standard suspension geometry accurately, I used Chris Gibb´s book and the associated Vortex CAD drawings.

See : Chris Gibb / Vortex Front Suspension.dwg

From this I could generate drawings to suit the McSorley 442 dimensions.

Chassis design is a very black art, but most sources I’ve found still seem to suggest the following (some maybe fact, some myth) :

  • The bottom arm should incline towards the chassis 10° (unacheivable).
  • The top arm should decline towards the chassis 20−25° (unacheivable).
    » Race & Rally Car Source Book
  • The top arm should be approx 2/3 the length of the bottom arm.
  • The roll centre (R.C.) should be 0−15cm from ground level.
  • Scrub radius should be minimised (inner 90% of tyre contact patch)
  • Camber gain 1° per 25mm of travel.
  • Swing arm radius should be twice track width (2.5 to 3.8m).
  • Swing arm radius change in bump to be minimised.
  • 1−2° Negative Camber for low roll centre cars.

Once the chassis, upright, track widths and ride height dimensions etc had been plotted, the Roll Centre (R.C.) and swing arm radius from the Instant Roll Centre / Instant Centre (I.R.C. or I.C.) could be approximated.

image: Roll Centre Calculations

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