Might as well stick MY foot into MY mouth on this topic. ;-)
In a message dated 9/20/2003 12:13:34 PM Eastern Daylight Time,
smacsjunk@hotmail.com writes:
> How exactly does the swing spring used on the late model Spits and
> GT6 Mk III improve the handling. I've seen in numerous magazine articles
> that it lowered the roll center, but from my limited understanding of swing
> axle geometry this appears to be a load of marketing hooey being parroted by
>
> the writers. Can someone clarify what's really going on.
As I understand it from various sources I've read over the years, it's like
this (sort of). Several folks have pointed out that, no, the geometry doesn't
change anywhere since all the various mount locations and such didn't change.
However, on the older setup, the transverse rear spring is tightly clamped
down
to the top of the differential. As I've seen it described (and the
terminology might or might not be correct here, but I hope you get the
point...and it
wasn't my terminology anyway. I'm NOT a suspension engineer. But I digress),
this rigid spring mount focuses the "effective roll center" of the rear
suspension at the top of the differential rather than "through" the
differential where
the half-shafts pivot on the u-joints.
On the swing-spring cars, only the main leaf of the transverse is rigidly
mounted, while the other leaves are more or less free to "rock" somewhat.
Again,
as I've heard it described, this lowers the "effective roll center" back down
roughly to axle (u-joint) level. Also, the decreased roll stiffness ultimately
led to OVERSTEER, which was compensated for by the fatter front sway bar.
> The reason for the question stems from Kas Kastner's remark in the MK 2 GT6
>
> tuning manual that swapping in a swing spring will improve handling in a
> roto flex car. I can't find anyone who has actually done this - anyone care
> to speculate on the theory behind this?
To my assuredly most unscientific mind, I don't see the swing spring as
lending any real advantage to the Rotoflex rear end, but then no one at
Triumph
asked me to write Competition Preparation Manuals, did they? :-)
As for what's best, I truly don't know. My old ex-GP Spitfire 4 "race car"
was setup in the mid- to late 1960s with all the factory or factory-authorized
racing bits, including both the competition rear spring AND the camber
compensator. And it stayed that way until 1983, when my friend and I bought
the
then-abandoned race car with a mind to having a cheap, fun autocrosser. Since
CHEAP
really was the operative word, we touched nothing on the suspension...and it
was just fine as an autocrosser for many, many years.
Bottom line(s): I like the camber compensator a lot on the earlier cars, both
street and autocross. It's a bit of a band-aid solution, but when the
band-aid you use was conceived by someone with the credentials of someone like
Mr.
R.W. "Kas" Kastner, ya gotta figure it's a pretty good band-aid, right? BUT,
having also autocrossed and street-driven "stock" Mk3 and MkIV/1500 Spitfires
off
and on for many years, I think ultimately the swing-spring is as good or
better. I'd as soon add a camber compensator to an early car as go to all the
added expense of properly updating the same car with a swing-spring AND fatter
front sway bar, etc., etc. At the same time, I'd probably leave the later car
pretty much as-is, since that setup seems to work fine.
Of course, there's always simply having a somewhat stiffer (i.e.,
"competition) early style rear spring and/or having that rear spring dearched,
which is
pretty much all that most of the Triumph "Works" competition Spitfires had
done
to them. And a good set of Konis never hurts on either version. And I've
rambled on enough about this.... :-)
--Andy Mace
*Mrs Irrelevant: Oh, is it a jet?
*Man: Well, no ... It's not so much of a jet, it's more your, er,
Triumph Herald engine with wings.
-- Cut-price Airlines Sketch, Monty Python's Flying Circus (22)
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