RE: Wandering, Negative Steering Roll Radius?

["Weiss, Dave " <Dave.Weiss@mkg.com>]

Scott Mo. and Graydon wrote:

>> for thought and ask does a change in wheel offset/width alter this
>> Negative Steering Roll radius enough to make the car more susceptible 
>> to wandering?

> Yes.  Possibly, or if you change the offset in the right direction, it 
> could even get better.

>> The V8 and 1991 200TQ 20V have different front hubs (441-407-615C) 
>> than the 1989-90 200 (447-407-615B) which I believe moves the wheel 
>> out further?

> I think I've heard that also.

>> What is the over all effect with the 35mm offset 15X7.5 wheels used 
>> on the V8 and 91 200TQ 20V?

> One would have to plot out the changes to determine if they changed 
> the negative steer radius.  If they changed the kingpin inclination 
> angle, that would affect it also.  I know they did this to the S4. 

> This was part of the reason for the mulitlink front suspension of the 
> A8/A4/A6.  With that design, the upper "virtual" ball joint is out by 
> the rotor which allows them to make the negative roll radius larger.  
> The downside is that you have much greater potential for slop in the 
> fornt suspension since you have twice the number of ball joints.

JG added: 

> Audi's "Negative Steering Roll Radius" is a fancy term for the more 
> frequently used "scrub radius."  On the 4000-based cars, it varies 
> between 12-14mm -- the exact number depends upon where the balljoint 
> is positioned) -- which means if you increase the offset of the wheel 
> by more than that -- say, changing from a 45mm offset to 24mm -- you 
> now have a positive scrub radius and all of the benefits that Audi 
> claimed from the design are gone.

S4 16X8's are 40mm offset...  Need to look at the rotor thickness, too.  
If someone wants to measure UFO's and 276's, I'll put calipers to the 
S6+ rotors.  Are the spindle and lower control arm dimensions the same 
on the 89's vs. V8's/91 200Q's?

At what point (in practical terms) does _increasing_ this force become 
detrimental?

Dave Weiss (still unsubbed and viewing via Web)
91 V8
98 CR-V