You wrote:
>
>> One draws an imaginary line from
>> the center of the contact patch, up through the axle pivot, repeats
it
>> on the other side, and where the two lines intersect that is is the
roll
>> center of that suspension. That, and ONLY that, is what determines
the
>> roll center of a swing axle suspension.
>*******************************
>Not entirely true, given two vehicles with the same suspension and
track, in
>this case swing axles, one a top heavy truck and the other a low slung
>go-cart, can you guess which one will roll first in a turn at limit?
Yep
>it's the truck. What you fail to take into account is weight
transferring
>during dynamic conditions not static. (read that book a little more)
Weight
>transfer among other things determines a cars roll center at speed. I
>guarantee that in the above example the roll centers are different
>regardless where the center of your pivot points are (which by the way
is a
>static roll center, not dynamic). There are a LOT of factors in
determining
>roll centers, way too much to condense all of them here and I'm not
about to
>get into a big debate about it.
>********************************
Barry,
It appears you are confusing "roll couple" with "roll center".
The roll center is entirely determined by the geometry of the
suspension hardware, and is as described by the other writer for a
swing axle suspension. There is a very nice discussion of this in the
January 1997 SCCA Sports Car magazine, specifically about the Spit rear
suspension.
The reason the truck rolls more than the car is that the center of
gravity is farther from the roll center. This is the "roll couple",
and is essentially the lever arm upon which the mass of the car acts in
rotating about the roll center.
The most important objective with the Spit rear suspension is to
reduce the roll stiffnes, so that the loaded wheel will compress up
into the fender, rather than jack down under the car. Both a camber
compensator and the swing spring do this.
Pete
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