RE: roll centers

["Steve Moresi" <smoresi@domain.elided>]

%-----Original Message-----
%From: owner-alfa@domain.elided [mailto:owner-alfa@domain.elided]On Behalf Of
%Peter Kemos
%Sent: Monday, November 26, 2001 10:48 AM
%To: alfa-digest@domain.elided
%Subject: roll centers
%
%
%Hey, don't let this thread die yet, lots of good discussion and
%information.
%Here's a question which Fred Puhn's book does not specifically address:
%How does one calculate front roll center on a double A arm suspension
%where the lower A arm is NOT parallel to the ground, but rather angles
%upward from the chassis to the hub/spindle/wheel assembly?  All of
%Fred's examples have the lower A arm parallel to the ground.

The analysis is the same, it is just that the A arm is not at what some
consider to be optimal (Parallel to ground).

%Extrapolating from his examples, the upward angled lower A arm would
%locate the instantaneous roll center quite high up on the vehicle, at
%approximately a height of the top of the tire.

Are you confusing instant center and (instantaneous) roll center here?
Extending the lines of the A arms gives the instantaneous center, about
which the tire is moving.  Then connecting that intersection with the
(opposite) tire contact patch gives the (instantaneous) roll center.  Now
the roll center will migrate as the suspension moves, so that is why I call
that instant too.

%If one were then to
%connect this point with the tire contact patch on the same side of the
%vehicle, it would result in a roll center well below ground level.
%If on the other hand one is supposed to connect the instantaneous point
%with the contact patch of the tire on the opposite side of the car, it
%would result in a relatively higher roll center (well above ground
%level) than if the lower arm were parallel.

This is why we want parallel to the ground lower A arms.


%
%Does this make sense to anybody?
%Could anyone please comment?  The car specifically is a 115 series GTV.
%
%Thanks,
%Peter Kemos


Steve Moresi
SLO, CA
74 Spider
64 Spider

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