to patch or...

[Lawrence C Leung]

As an engineer of nearly a decade(no longer practicing), and a current
physics teacher, as well as a competing sports car racer, the basic
principles of the gas laws apply to the tire contact patch issue. Plain,
and simple. 

Sure, in actual application, one has to apply the specifics of the
situation, such as weight distribution, dynamic status of the vehicle,
spring constants of the tire carcass and rubber in static and dynamic
states, damping rates (which effect corner loading, oh, did I already
mention dynamic weight distribution), etc, etc, etc. In my recollection,
the poster was trying to get a GENERAL idea on what effected hydroplaning
in a vehicle, and this discussion transitioned back into the tire patch
size issue discussed several months ago. Since I didn't feel we needed to
back through this ALL OVER AGAIN, I stated a general principle. 

IN GENERAL, tire patch size is directly proportional to the weight of the
vehicle, and inversely proportional to the pressure in the tire, all
other factors being equal. This holds extremely well within any given
brand and type of tire, and within any given vehicle, in normal and even
under extreme performance situations. It only begins to noticably fail as
a principle in the case of an EXTREMELY underinflated tire. If you wish
to explore a tire's contact patch size variation under these completely
useless conditions, go ahead, even there the principles of physics and
engineering hold, it just becomes mathematically even more difficult to
model. What is best considered in the patch vs. weight vs. pressure model
is not the absolute patch size (though this is close anyway!) but the
CHANGE in patch dimension in relation to pressure and or weight. The
absolute patch size relation is a reasonable model, at normal operating
pressures, weights, and transfered loads. 

Is the absolute optimum model of the situation a complicated one? Yes, I
agree it is. Can the general public make an informed decision and gain a
good understanding of the situation based upon the basic physics
principles that underly all of the complicated engineering issues
mentioned in the original post here. You bet!  So, if you understand the
spirit of the original post, great!. The previous post I made nor this
one were not intended as an engineering thesis on the design of
automotive tires. If you wish to persue it more, go search the archives.
Then decide if you need to continue this further. 

'nuff said, I'm through venting....

LL - NY

On Fri, 2 Feb 2001 10:56:30 -0800 "Tihol Tiholov"
<ttiholov at rodeo.sd27.bc.ca> writes:
>l.leung at juno.com wrote:
>
>>It works exceeding well. Only in extreme conditions (like there being 
>no
>>internal air pressure, or exceeding stiff sidewalls such as trailer
>>tires) does this begin to be a little less proportional.
>
>So, to paraphrase: It works exceedingly well, except when it doesn't 
>work
>
>then he wrote:
>>It's a
>>straightforward application of physics.
>
>If physics was enough to build something, the engineers wouldn't 
>study other applicable/practical disciplines and wouldn't need to 
>experiment a lot; not to mention that all tires would be made of more 
>
>or less the same material, so one company would hire chemistry 
>specialists, the rest - industrial spies :-)
>
>All knowledge is a bunch of relative truths and I thought that the 
>conquest for an absolute truth has at least subsided as of late, 
>despite the hope that it can make our lives nice and simple...
>
>Anyway, I don't know the whole truth either
>Have a good weekend yeall!
>
>Tihol