GTV6 suspension geometry

[graham.hilder@xxxxxxxxxxxxx (Graham Hilder)]

This is a bit belated but thanks for Chris's, Scott's and Simon's
posts in Digest no.122 etc, regarding the 116 front suspension,
and the effect on understeer of stiffening the front end. Indeed, it
does look like the camber-control effect of the stiffening more than
counteracts the weight-transfer effect, so the nett result is
reduced understeer, rather than increased as might traditionally
have been expected at the stiffened end.  Fred Puhn's
handling-book (mentioned by Simon) re-confirms in as many
words that this can often be the case.

However, I am a little doubtful about one issue which came up,
which is where Scott proposed that if you lowered a standard 116
suspension (which was: unequal length wishbones, with lower
one originally sloping down below the horizontal), then the new
starting-point of the suspension will be closer to the positive end
of the camber curve and so will understeer very early, rather than
only when really pressed as it did at standard height.  I'm not sure
about this.  Why not? Because I think that, although it's true that
suspension-compression will not now add neg camber as quickly
as it would have before, on the other hand the lowered car should
be rolling less for a given g-force, so the roll won't be adding
positive camber as quickly as it would have before (as was
mentioned in Chris's post, Digest 122).  So perhaps the NETT
result of the lowered car, whose lower wishbone now starts nearer
the horizontal,  could well be less understeer, not necessarily more
as Scott proposed. I feel it all depends on how your lowering has
changed TWO aspects: not only the rate at which the suspension
adds neg camber when compressed, but also the reduced body
roll moment, and hence roll angle.  Depending on geometries &
stiffness, the nett result on camber-while-cornering could go
either way I feel.  Oh, and there may be a third factor.... I gather
that the front lowering would reduce the roll-moment and hence
reduce the weight transfer at the front, which I believe should
tend to reduce the under-steer. So apparently the lowering
introduces two changes tending to REDUCE understeer, along
with Scott's camber change effect which tends to increase it, so
Scott's conclusion may not always hold true.  

I do know that my Alfetta,  slightly lowered and slightly stiffened,
feels a hundred times less of an understeerer than before.  Trouble
was, as always, both mods were done at once, so I don't know
which did what!  Had I lowered it alone, would it have
understeered sooner as per Scott's proposition?  I guess I'll never
know for sure.   

In Digest 124, Dave wrote that his lowered-only Alfetta was a
terrible under-steerer, but was vastly improved after suspension
work, including (in particular) restoring the original height.
However I don't know that this really can be taken as confirming
Scott's proposition, for the same reason as my case just
mentioned: Dave had too many other things changed at the same
time as the height (stiffened front, stiffened rear, new bushes, etc).

All very intriguing.
Best regards,
Graham H,
N.Z.

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