acg@hermes.dlogics.com asks:
>Any typos above are the responsibility of the Sun-Times! Maybe someone
>can enlighten me about what the "-IRS" suffix means. Nice to see an ad
I've always assumed that "IRS" stood for independant rear suspension.
Have I been laboring under a false impression?
No, the IRS designation does mean that the TR4A has independent rear
suspension. Most TR4As did; I know that TR4s were solid-axle but I
seem to recall that a very very few As also came with leaves.
The thing I would like to have explained is what the heck a "swing
axle" is. Is it just another term for a solid rear axle/diff slung from
leaf springs, or is it some incredibly arcane British suspension
treatment?
Heh. It's not often I get to make fun of Spitfires and Porsches in
the same tirade... :-)
The swing axle is a sort of semi-independent rear suspension. Basically,
there is only one universal joint (or flex coupling, or CV joint), at
the inboard end of each half-shaft. This lets the wheel swing up and
down as the car traverses bumps. Unfortunately, there are some flaws
in the design when you approach the limits of the car's handling,
mainly that the wheels tend to "tuck under" if you brake while turning.
That is, if the rear of the car lifts (say, under heavy braking), the
wheels effectively drop, and the fact that they're at a fixed angle at
the end of the half-shaft makes them tilt so that they're riding on
the edge of the tires. In extreme cases, this can cause the car to
spin. (Porsches were more noticeable in this regard because they also
had the engine and its inertia at the rear; it made them very easy to
get turning, in the hands of an expert, but hard to stop, in the hands
of a neophyte. Porsche fixed this along about 1964 or 1965 when they
introduced the 900-series cars, as well as on several of their racing
cars before then.)
This is only an issue in extreme circumstances, such as autocrossing
or a dire on-the-road emergency. Under normal driving conditions,
it makes for a slightly more comfortable ride and actually helps with
adhesion on bumpy surfaces because a blow to one corner won't upset
the opposite wheel as it can with a live axle.
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