Re: Wheelspin

["Jeremy R. King" <jrking@ces.clemson.edu>]

Eric.  The traction and slip angle you're referring to have to do with
cornering power.  Sure the maximum tractive force is achieved at the
optimum slip angle.  But that angle is the angle made by the path of the
contact patch vs. the angle of the rest of the tire.

Attempted ascii art:

        ______
       |      |
       |      |
       |      |
       \      \    Angle of deformation of the contact patch.
        \      \
       |      |
       |      |
       |      |
       --------

This is a crude sketch, but hopefully y'all get the picture.  This
deformation creates a force normal to the direction of tire travel
commonly known as cornering force.  Once the optimum slip angle is
passed, the cornering or tractive force decreases - this is why you can
reach a point where if you steer a little more, the steering effort gets
lighter.  The tire contact patch can't deform any more and starts to
slide.

If you have questions on any of this, refer to "Race Car Vehicle
Dynamics" by Milliken and Milliken or "How to Make Your Car Handle" by
Fred Puhn or anything by Carrol Smith.

In all my reading, I've never noticed the term slip angle equated with
wheelspin.  All wheelspin does is allow your engine to reach it's torque
band more quickly.  Traction actually goes down.

Jeremy R. King
Suspension Team Leader
War Eagle Motorsports '96

STEADIRIC@aol.com wrote:
> 
> >Question #1: Um.. you mean for maximum *performance*, maybe?  I'm kinda
> >hard-pressed to see how 10% slip gives you more traction than no slip.
> 
> It all has to do with elastic deformation and the generation of the
> Maximum Coefficient of friction which occures at some degree of slip
> which for a street tire is about 10% For more detail (It's really nerdy)
> get the SAE paper written by Harvey and Ressler.
> 
> >Question #2: Semantics aside, WHY?  I don't doubt you, I just want to learn
> >more about this.
> 
> See #1
> 
> Later!
> 
> Eric Fletcher
> '87 5KCSTQIA2RSR2B
> St. Louis, MO
> 
> STEADIRIC@aol.com

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Jeremy R. King  Clemson University, S Carolina, USA
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