From: potamian@hpl.hp.com (Spyros Potamianos)
Newsgroups: rec.autos.sport
Subject: Re: Tires : Slicks vs. Treaded: Help Pleas
Date: 7 Oct 92 16:04:00 GMT
Article-I.D.: hplabs.BvrDyp.8IB
Organization: Hewlett-Packard

andyw@meaddata.com (Andy Welter) writes:
>
>In article 718451041@vipunen.hut.fi, bassek@lesti.hut.fi (Basse Kankkonen) writes:
>>It ocurred to me that the formula of friction is F=u*m*g
>>(u=constant of friction,m=mass,g=acc. 9.81m/s^2)
>>This means that the traction is not depending on the area.
>>	[ stuff deleted... ]
>I believe that formula for friction is a simplified one that does not take into
>account all variables.  I don't believe this takes into account the shear strength
>of the materials in question.  The contant of friction (u) is assumed to be constant
>within the range of mass in question.  
>       [ stuff deleted... ]
>---
>|Andrew Welter	     |  All views are mine and not |      (513) 865-6822   
>|Mead Data Central   |    that of my employer      |      pd&o-ps-ts-dsp       
>|P.O. Box 933        |                             |     andyw@meaddata.com
>|Dayton, Ohio  45401 |          	           | ...!uunet!meaddata!andyw

I agree, as Carrol Smith says in his (excellent) book "tune to win":
"The racing tire does not follow Newton's Laws of Friction - which are for
friction between smooth bodies".
Apart for the examples mentioned in the previous articles, it also quite
"impressive" that the friction generated by a tire is *not*
proportional to the vertical load (the function is sublinear, i.e. if
you double the vertical load, the max friction that can be generated by
a tire increases but does not double).

And for sure tire width increases friction (otherwise they wouldn't use
wide tires in racing). At least in dry roads... Has anybody noticed the
ridiculously skinny tires some rally cars wear when they are racing on the
snow??? (while the same cars use much wider tires when racing in paved
roads)

BTW, (changing the subject) one of the things I really liked in Smith's
book is the "statement of non-liability". I found it very refreshing,
especially after reading a recent thread on the widow of Mark Donahue
suing Goodyear for the death of her ex-husband. Here it is copied without
permission:

       Our society has reached the point where I am advised that,
    in order to protect myself from possible lawsuits, I should include
    a statement of non-liability in this book. Since I believe that the
    human being is wholly responsible for his own actions, I strongly 
    object to this necessity and to the morality that has spawned it.
    However, I would object even more strongly to being sued - so her it
    is.
       The price of man in motion is the occasional collision. Motor
    racing is dangerous. In order to be competitive in this business it
    is necessary to operate at the outer edges of the performance
    envelope. The closer we come to the edge, the greater risk of falling
    off becomes. This book is about improving the performance of the
    racing car and its driver - particularly with respect to the
    roadholding department. It deals with the deliberate exploration of
    the outer limits of traction. The closer the racing car approaches its
    potential in this department, the less forgiving it becomes and the
    greater the chances of paying a sudden stop type penalty become when
    an error in judgment occurs.
       If, while attempting to apply any of the ideas, procedures or
    advice contained in this book, you should come unstuck, you will have
    done so through you own conscious decision. I disclaim responsibility
    for your actions - and for your accident.

Spyros Potamianos
potamian@hpl.hp.com
Newsgroups: rec.autos.sport,rec.autos.tech