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From: Doug Milliken <bd427@freenet.buffalo.edu>
Subject: Re: Understeer in open wheeled sims are gonna get better
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Date: Tue, 8 Dec 1998 04:57:14 GMT
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On 7 Dec 1998, Jim Sokoloff wrote:

> This depends on the castor of the wheel. If the effective center of
> the (sliding) contact patch is to one side of the axis about which the
> wheel can pivot, there will be an aligning torque.

Since this has gotten pretty technical, it's time for some standard
terms...even though I swore off this thread earlier...!

Aligning Torque (AT) is the torque about a vertical axis (SAE "Z" axis)
through the axle and the wheel centerplane.  It is one of the tire forces
and moments and is independent of steering and suspension geometry.  It's
primarily a function of slip angle and load.  It's not quite zero when
the slip angle is zero (tires don't really run quite straight).

Trail results from Castor angle and/or Offset in the steering geometry. 
Tire lateral force at the ground produces a torque about the kingpin.

Steering torque about the kingpin is a combination of the AT and the
lateral force x trail torque.  Then to get it up to the steering wheel
there is a gear ratio, and (usually) quite a bit of friction.
 
-- Doug
		Douglas Milliken  <bd427@freenet.buffalo.edu>
		Milliken Research Associates Inc.



