johncof@ibm.net writes:
<<
1. An anti-roll bar is just a linear rate torsion spring. Only the center
part of the anti-roll bar transfers the load and it could care less about
the lengths of each end. The center part of the anti-roll bar sees both bar
ends as one lever (which is the combined lengths of the two bar ends).
Each end is totally dependent on the other because you can't disconnect one
end and have the bar still work on the other. >>
That was the whole basis of my argument regarding moment/torsion and force
differentials in a sway bar. I'll agree that the roll differential from side
to side will be minimal, because the amount of roll in most performance
oriented sports cars is small to begin with; on the order of ~3 degrees.
However, the force differential will not be as insignificant for a production
type vehicle because the magnitude of the forces are significantly greater
than the magnitude of the roll (considering the weight forces involved with
the size of the bars and their tire loading contribution relative to the
overall tire loading force).
As an example, the the differential in the arm lengths of the adj. front bar
on my Z3 coupe are ~10%. If you go back to my original moment argument where
it was proven that the the forces side to side are proportional to the
differential in the arm lengths, it's then apparent that differential in the
forces at the arm ends on this particular bar when adjusted to it's opposing
extremes will also be 10%. Now if you still want to argue that a 10%
differential side to side in swaybar tire loading doesn't make a difference
on the typical production sports car, well I've done and said all I can to
convince you that the reality is it does make a difference when pushed to the
limit of adhesion. There'd be no sense in me carrying this any further.
Again, it is true that the center of the bar carries the brunt of the
torsional spring rate and is constant (within reason). It is also true that
the end lengths aren't important with regard to the torsion load the bar
sees, but become important once the constant torsional load forces are
transferred to the suspension and that the forces transferred to each side
will not be equal when the end lengths side to side of the bar are not equal,
as proved by moment argument. Further, it is also true that the differential
of the forces applied to the suspension by an unequal arm length swaybar will
be directly proportional to the differential of the unequal arm lengths.
Where we disagree is in the perception that the bar sees the arms acting as
one lever. It seems to me that your argument is still trying to twist (no
pun intended) the one lever arm argument into equating the forces side to
side. The forces side to side resulting from the torsion being transfered
through the arms and to the suspension can only be equal when the arm lengths
are equal. You can argue against the laws of physics all you want but thems
the facts, Jack. Whether or not the resulting differential in forces are
significant or not will ultimately be dependent upon the resultant magnitude
in the contributing differential tire loading forces applied by the unequal
length bar relative to the magnitude of the overall tire loading forces.
The contributory tire loading forces from a small bar+ stiff springs+ light
vehicle weight (real race car) will be less significant than a thick bar+soft
springs+heavy vehicle weight (street production car), of course ultimately
determined by the actual differential in swaybar end lengths.
M Sipe
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