Re: Changing the roll center of a suspension

["George Schweikle" <schweikg@domain.elided>]

Nizam,

I don't have my "How To Make Your Car Handle" book handy, but here's what I
remember: the front and rear roll center points must be connected to
establish the roll axis. Think of this as the longitudinal line that the
entire car rotates around as it leans. This really establishes the basic
handling characteristic, and to define this axis requires knowing both the
front and rear roll centers. I'm not sure about the roll axis of a GTV-6,
but the 105 Spider/GTV has the roll axis angled downward from rear to front.
This why stock Spiders seem to want to corner on their outside front wheel
as the rear of the car hikes up. The Panhard bar kits sold for 105-chassis
cars move the rear roll center from the T-bar attachment at the top of the
differential to the level of the Panhard bar under the diffential. A drastic
change of 8-10 inches that improved the handling of my Autocross Spider. I
believe the GTV-6 Watts link already provides a fairly low rear roll center
at the center link pivot on the DeDion tube, but don't know how this
compares to that of the front suspension. Calculating the roll center of
independant front suspension is more complicated, but the Fred Puhn book has
some excellent material on this topic.

How about some comment from the racers out there?

Regards,

George Schweikle
Lexington, KY
76 Spider
87 Milano

----- Original Message -----
From: Nizam Zambri <nizam@domain.elided>
To: <alfa@domain.elided>
Sent: Monday, November 19, 2001 8:35 PM
Subject: Changing the roll center of a suspension


> Hi guys,
>
> There has been lots of talk lately about shocks, and springs.  Zamani
> also brought up drop spindles and upside-down balljoints.
>
> What we are really trying to do is to move the roll center further down
> in a chassis.  >
> I had a brief conversation with Larry at APE and he didn't think this
> was a good idea.  However, I'll keep his reasoning for later because I'd
> like to hear what the forum has to say on the subject.
>
>  ...some of you may think differently.  What
> say you?
>
> Nizam

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