[DeTomaso] Stiff springs and 1" sway bars! (was Re: De Anza Autocross)

MikeLDrew at aol.com MikeLDrew at aol.com
Tue May 17 00:21:05 EDT 2011


In a message dated 5/16/11 20 26 26, julian_kift at hotmail.com writes:


> That argument does not seem intuitive to me, even though the wheel is 
> wider with a greater contact patch and more out board it is still reacting 
> through the same wheel flange and then through the same a-arms and pivot 
> points.
> 

The total lever arm is based upon the relationship between the center of 
the contact patch, and the A-arm mount on the chassis.   The fact that the 
force is being transferred between the flange of the wheel and the upright at a 
given point is irrelevant.   They are firmly fixed to one another, and thus 
can be erased from the equation and considered as a single entity.   On the 
widebody cars, the lever arm is a fair bit longer due to the fact that the 
contact patch is so much further outboard of the spring mount on the A-arm.  
 So the wheel rate is higher, i.e. the wheel exerts a greater force on the 
suspension by virtue of the fact that it is further away from the A-arm 
mount.   Thus the spring needs to be stiffer to offer the same level of 
resistance that would be given to a narrower wheel/tire combo with the center of the 
contact patch closer to the A-arm mount.

You can spend all day searching websites for various mathematical 
calculators for figuring out wheel rate, etc.   I'm lucky enough that Goran Malmberg 
gave me a copy of his book on race car chassis design. :>)

Mike



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