Re: DeDion

["Dean W. Cains" <dwc@domain.elided>]

Hi Kyle:

A deDion suspension hopes to combine the beat aspects of both a solid rear 
axle and a fully independent rear suspension.

In a system such as on a Spider, with a solid rear axle, both wheels are 
always exactly parallel to each other, and hopefully always perpendicular 
to the road, both of which are good things.  The bad part is that the 
entire mass of that axle (including the wheels, tires, brakes, etc.), and 
all the components that hold it to the chassis (like the trunnion, trailing 
arms, etc.), have to move together.  Their combined masses have quite a bit 
of inertia, which makes them want to change velocity and direction less 
quickly than might be ideal, as the car traverses a rough road surface or 
changes attitude    .

A fully-independent system would have the differential firmly fastened to 
the chassis, so only the halfshafts with their locating arms, and the 
wheels/tires/nub carriers/brakes have to move with changes in the road 
surface or car attitude.  Ideally, there is less mass to move around (in 
some cases, even the brakes are inboard and fastened to the differential), 
but the wheels may not always be optimally aligned with the road surface at 
all times.  There may be quite large camber changes at different points in 
the travel of the suspension, for example.

As I said,  deDion tries to be the best of both.  The differential and 
brakes (at least on an Alfa) are mounted to the chassis, so moving mass is 
reduced to almost just the wheels/tires/nub carriers. But, there is also a 
floating framework that connects both wheels to each other, keeping them 
parallel, as with a solid axle, while the suspension moves in response to 
the road.

There are probably great and poor examples of each different type of 
system, and further analysis would reveal finer design points such as 
higher or lower roll centers, mass of the entire system, etc. that would be 
more important in a race car over a street car.  In the opinion of many, 
Alfa has done a respectable job both with the solid axle and deDion systems.

At 11:55 PM 9/9/2001 -0400, you wrote:

>Date: Mon, 10 Sep 2001 02:57:22 +0000
>From: "Kyle Chenier" <klyde67@domain.elided>
>Subject: DeDion
>
>okay. excuse the stupid question. would someone explain what DeDion is?
>
>kyle




Regards,

Dean W. Cains
dwc@domain.elided

'74 2000 Spider Veloce
Lutz, FL

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