Suspension Geometry - The Expert Suite of programs
The Future of Suspension Geometry Software
Assembling a Suspension from Parts
Since the dawn of personal computer suspension geometry software
some 25 years ago kinematic analysis has meant defining static suspension
geometry points and calculating how the suspension parameters react as the
chassis moves dynamically. Camber, toe, caster and the anti-values change as the
chassis moves vertically,
rolls and pitches. Steering inputs add another dimension of analysis including
Ackermann.
But this is really only the second half of suspension geometry analysis. The
first half, previously ignored, is how you build a suspension and then measure
the static suspension points. Chassis mounting points are best measured on a
surface plate before the suspension is attached. Uprights and A-arms are most
accurately measured before being mounted on the car. This is certainly more
accurate than trying to crawl under a car and place a tape measure near the
center of rotation of a ball joint attached to an a-arm.
Analysis often must be performed before the car is assembled and
tires mounted. The selection of parts may even depend on the desired static
suspension parameters: camber, toe, caster and track. The actual suspension is
assembled from the chosen parts. This reflects the way professional racing
teams, certainly stock car, actually build a suspension.
Accurate analysis requires precise measurement. Locating the
center of rotation of a ball joint is difficult. Trying to measure the movement
of a ball joint resulting from camber shims is extremely difficult. Suppose you
want to change static camber one degree more negative. Camber shims on the upper
a-arm will move the upper ball joint about one quarter of an inch. But are you
also aware those camber shims will lower the lower ball joint over 1/8 inch It
will also move the tire contact point outward 1/8 inch while moving the hub
center 1/8 inch inward? Can you measure these changes when you add camber shims?
The Fixture commands - updated and expanded
The Fixture capability in WinGeo3 does measure the upright in it’s
own coordinate system. The Expert version uses these same measurements but adds
off car measurement of the upper and lower A-arms. Confusing modes like "Rotate
about the Lower Ball Joint" in the Fixture calculations are replaced with more
general constraints. For instance, "Rotate about the Lower Ball Joint" is now
"Constrain the Lower A-arm." With the Expert version spring and shock
attachments may be measured off the car and these points will move as the A-arm
moves. Add camber shims and the lower ball joint moves. This means the Lower
A-arm rotates and the spring, shock and antiroll-bar attachment points also
move.
Part Measurements - The "Jig"
Parts can be measured off the car. The term "jig" refers to these measurements,
which may be measured in a jig or on a workbench. The upright / hub / wheel is
measured off the car with the hub lying flat on a surface. (These are equivalent
to the Fixture measurements of earlier programs.) These measurements can
be saved in a file and opened by part number..
The upright is shown in rear and plan views.
The side view is also available
The Upper A-arm
The Upper A-arm is measured off the car in a plane which goes through the ball joint and the inboard pickup points. These measurements can be saved in a file.
