[ROVERNET - UK] P6 Rear Suspension Function

Vern Klukas vern at inkspotco.com
Mon Apr 7 17:50:03 BST 2008

>Steven Dibdin wrote:
>>No, both systems have the DD tube conected to the hubs for the same 
>>reason; to try to keep the both wheels prependicular to the road 
>>surface. Neither are turely independent systems. The idea is you 
>>get the pluses of the independent's low unsprung weight (good for 
>>ride and handling) and the live axle setup (wheels planted firmly 
>>to the road by maintaining camber independant of suspension 
>>travel). As a way of doing things it works pretty well but with 
>>some new compromises.
>'Splain it to me some more...
>I understand the camber advantages, but maybe I'm not clear on the 
>way the tube works. As far as I can see the tube is simply bolted to 
>the wheel hubs in a static manner. The two halves of the tube slide 
>laterally, but they do not rotate with respect to each other, and 
>the tube is stiff.

The two sections of the tube do rotate in relation to each other, the 
rest of the compliance (flexibility) is created by flexing of the 
trailing arm rubber bushes

>Therefore, when one bounces or leaves the road, I would think that 
>the other wheel would have to be affected.

With one side on the bump-stop, there is a small camber change 
relative to the opposite wheel, but it is several times less that the 
camber change of most IRS suspensions. But keep in mind that this 
talk of camber change is not about the movement of the wheel over 
bumps. It is about controlling camber change as the car body rolls 
under the influence of cornering forces, an entirely different kettle 
of fish.

As for the effectiveness of the P6 vs SD1, on a smooth surfaced road 
there is probably not much between them, but introduce a rough road 
with potholes, undulations and camber changes and the P6's rear 
wheels will stay planted while the SD1 rear axle will be dancing 

>In fact, I'm not sure why something doesn't break.  If the two wheel 
>centers are on the same plane and the camber is fixed, how can one 
>wheel go over a bump without changing the camber of the other wheel 
>just as it would in a live axle setup? Are you saying that the 
>DeDion tube flexes? I can't see where it is designed to do that.

Actually, just about everything flexes. For example, did you know 
that under hard cornering a standard steel wheel rim will deflect by 
a half inch or so, depending on the diameter of the wheel. It's why 
rims occasionally fail with the centre breaking away from the outer 
section of the wheel.

>I've read the theory, but how does it actually work?


Vern Klukas                             I'm a little . . .
Inkspot Type & Design
vern at inkspotco.com

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