Re: Watts Linkage on Milanos and GTV6

[James Montebello <jamesm@domain.elided>]

The Watts linkage doesn't function as a sway bar in any way.  It allows
either end of the DeDion or the whole thing to move freely up and
down, but not at all side to side.  It's not completely intuitive just
looking at the thing, but if you draw a couple of simple diagrams,
you'll see that's how it works.  All three points on the center link
are meant to pivot freely, as are both of the outer ends of the links.
The semi-trailing arms primarily locate the DeDion tube fore-aft.
The Watts linkage locates it laterally.

Earlier, live axle Alfas used either an A-arm or a T-bar to provide
lateral location, and simple trailing arms for fore-aft location.
The Watts linkage was probably chosen for the DeDion because the transaxle
occupies the area the T-bar would normally live in.  It also has some
roll-center benefits.

A sway bar is supposed to resist the body rotating with respect to the
suspension (i.e., body roll).  It's meant to keep the *body* relatively
parallel to the ground, not the axle.  On a live axle or DeDion, the only
time the axle isn't parallel to the ground is when you've lifted a rear
wheel off the pavement. :-)  Sway bars also strongly influence weight
transfer across the car in cornering, and so have a strong influence on
transitional handling effects, like turn-in.  On completely independent
suspensions, like the front of a GTV6/Milano, they also affect camber
change in cornering, since body roll causes positive camber on such
suspensions.  On a live axle or DeDion, sway bars have no effect on
camber change, since, again, the tube is always parallel to the ground
so the wheels are always perpendicular to it.

My GTV6 has a rear sway bar, and I believe they came that way from the
factory.  Can't say for sure about the Milano or any other transaxle car.

james montebello

On Mon, 11 Feb 2002, John Cecil wrote:

> This may be a duh... question, but exactly what does the Watts linkage
> accomplish on the late model De Dion Alfas? If one looks at it, it would
> appear that it does something similar to that an anti-sway bar would do,
> i.e., maintains the rear axle more or less parallel with the road when
> assymetrical cornering cornering loads are experienced.  The
> semi-trailing arms locate the De Dion tube relative to the chassis and
> neither  Alfa Milano/GTV6  have an anti-sway bar. The Lancia Flaminia
> and Aurelia, which also used a De Dion rear suspension, but with
> semi-elliptic springs, did not use an anti sway bar either. So ...
> inquiring minds would like to know the real function of the Watts
> linkage of the Alfa Milano. Incidently, the Caterham version of the
> Lotus 7 use a De Dion, a Watts linkage AND an anti-sway bar. What
> (Watts) going on here?
> Regards,
> John Cecil
> <jcecil@domain.elided>
> <jcecil@domain.elided>
> <http://home.earthlink.net/~jcecil66/index.html>
>
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