Re: Roll stiffness and cornering

[DeWitt Harrison <de@aztek.com>]

I wrote:
>>As a minor digression from the main thread, I am curious why the
>>use of shorter tires would have any bearing on the suspension
>>geometry.  On the face of it, a shorter tire just brings the road a
>>bit closer to the car's CG without changing any of the geometric or
>>dynamic relationships.
Then you wrote:
>Shorter/taller tires also affect the roll center(s), scrub radius, etc. ...
>sometimes this can be helpful and sometimes it screws things up, depending
>upon the car, its intended use, etc.  I'd make a sketch to show this but I
>think it'd be virtually impossible to do in ASCII given the small
>differences involved...     
> _________________________________________________________________________
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>    / |      _| o    | \       _| o     Jeffrey Goggin
>   /__| | | / | | __ |  | | | / | |     audidudi@delphi.com
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> _________________________________________________________________________

Scrub radius: you're right. I estimate roughly a 0.1" change with the tire
size change you specified.  Would this typically require compensation
elsewhere in the geometry? Roll center change: you're right again. I forgot
the center of the contact patch is on the line that locates the roll center. Am
I correct in betting the roll center height increases relative to the CG with
shorter tires? But then the CG gets closer to the road. If so, wouldn't it
be possible that the net height of the roll center relative to the road remains
roughly constant when you switch to the shorter tires?

DeWitt