Re: GTV6 suspension geometry

[Chris.Prael@xxxxxxxxxxx (Chris Prael)]

> Date: Tue, 22 Sep 1998 12:16:32 +1200
> From: graham.hilder@domain.elided (Graham Hilder)
> Subject: GTV6 suspension geometry (WAS Tyres for GTV6)
> 
> In no.119, Chris touched on the GTV6 front suspension geometry,
> including :
> 
> >>>>>>>>>>>>>>>
> .........about the geometric limitation on cornering speeds, the front
> geometry of the GTV6 keeps the outside tire perpendicular to the
> pavement through approximately 15 degrees of body roll.  With
> greater roll, the outside front wheel camber goes positive, quite
> rapidly......... Classic, designed-in geometric understeer.
> >>>>>>>>>>>>>>>
> 
> I wonder if Chris (or others) would like to go into this a
> little further please, to explore the following lines of thought.
> 
> Firstly, I wonder if this an explanation for the generally-accepted
> result that stiffening up the front of an Alfetta/GTV6/etc will
> reduce its understeer, rather than increasing it as conventional
> textbook wisdom might suggest. 
> (Although based on Chris's info above, I guess that what it would
> really mean in this case is that the ONSET of major understeer
> would be delayed, rather than understeer being generally reduced
> across the whole band).

Precisely!  
> 
> Secondly, is it the use and the particular layout of unequal length
> wishbones which gives the camber result Chris describes ?

I would assume that this effect was designed in.  Though I have no proof.
> 
> And if so, how would his 15 degrees figure be altered if the car
> is lowered, with consequent changes to the wishbones' initial
> angles?    I.e. would the +ve camber occur at a lower or higher
> angle of roll?   Since I don't have the details of the wishbone
> lengths, mounting points and initial angles from horizontal, I can't
> work this out for myself, but possibly Chris or someone else
> already knows......

Note that the 15 degree figure is an estimate.  I could be off by a fair
number of degrees, either way.  It would be interesting to instrument a car 
and get the real number.  

Similarly, I would be interested to learn whether correcting the ride height
to European spec. changes the roll angle at which gross understeer sets in. 

Even if there is no change in the roll angle, reducing the ride height
shortens the roll moment arm, which means that gross understeer should set in
at a noticeably higher level of lateral accelleration.  (Translation into
English: you should be able to corner a lot faster before the front end washes
out.)
> 
> Intriguing stuff !
> Best regards,
> Graham H,
> NZ. (Alfetta, GTV, Alfasud)

Cheers,
Chris Prael

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