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

[Tomas Gunnarsson]

This is not correct Mike. It's true for a swing arm suspension but not a
double A-arm suspension. The leverage will change but the reference
distance is not the center of tire to chassis mounting point, it's
center of tire to virtual rotation center for the suspension. This
distance is much bigger than the A-arm length so the change in ratio is
much lower. In an equal length parallel arm system the wheel offset
would theoretically have no impact at all on the wheel spring rate.
 
Tomas

<-----Ursprungligt Meddelande----->
From: MikeLDrew at aol.com [MikeLDrew at aol.com]
Sent: 17/5/2011 6:21:53 AM
To: julian_kift at hotmail.com; thomas at hax.se; detomaso at realbig.com
Subject: Re: [DeTomaso] Stiff springs and 1" sway bars! (was Re: De
AnzaAutocross)

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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