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  • From: "Bill Geschwind" <geschwin AT email.unc.edu>
  • To: "'Internetworkers: http://www.ibiblio.org/internetworkers/'" <internetworkers AT lists.ibiblio.org>
  • Subject: RE: [internetworkers] Surveillance, USA
  • Date: Wed, 9 Apr 2003 08:25:17 -0400

Another variable to throw in to the equation would be the state of
inflation of each tire and the amount of wear on each tire. If a tire
develops a slow leak, the diameter of the tire could potentially
decrease by several millimeters until it appears "soft" before the owner
does something about it, such as re-inflate it, or get it fixed or
replaced. Also, a brand new tire has a slightly larger circumference
than one on which the tread has worn off. The rate of wear of the tire
and, in the case of a slow leak, the rate of deflation is not
necessarily constant or easily predictable.

- Bill

-----Original Message-----
From: internetworkers-bounces AT lists.ibiblio.org
[mailto:internetworkers-bounces AT lists.ibiblio.org] On Behalf Of Shea
Tisdale
Sent: Wednesday, April 09, 2003 12:05 AM
To: Internetworkers: http://www.ibiblio.org/internetworkers/
Subject: Re: [internetworkers] Surveillance, USA

That was my thought also. I don't beleive the Auto manufacturers have
much
to do with tires. Adn any critical thought on the issue would blow many
holes in the idea. Here is my 5 minute 'debunking'.

Technologically speaking, if this was going to be done, it is much
simpler
to build the device into the on board computer. Since 1996 the EPA has
required OBD II or On Board Diagnostics version II. This computer
system
controls how your car runs and has been in almost (99% or better) every
car
sold in the United States. This system knows about the speed of your
car
and a whole host of other information (100 or more sensors), including
in
some cases the acceleration and braking g-forces. And in many cases can
store information for long periods of time. So that's a location that
already has the information and that the auto industry actually has the
ability to modify.

And then you have the issue of it being a tire. First, tires are
frequently
subjected to horrible shock, vibration, puncture, and tremendous
centrifugal
forces. That's a great place to put sophisticated electronics like
accelerometers, transponders, and the like. Second, a transponder in a
tire
would have to be pretty sophisticated and specifically tuned to each
individual tire to determine a vehicles speed. To determine the speed
it
will need to know the diameter of the tire and the rotational velocity.
To
determine diameter it would have to know sidewall height * 2 plus wheel
diameter. Sidewall heights are in millimeters and wheel diameters are
in
inches. So convert sidewall height into inches. Anyway, take the
results of
that equation and then multiply it by Pi and you have circumference.
Take
that number and multiply it by the number of revolutions over a given
time
period and you should be able to determine speed. Third, your have to
four
of them. Four signals? And with four signals you would probably
actually
receive four different speeds since all the wheels don't spin at the
same
speed unless you are going perfectly straight. Fourth and lastly, tires
don't have power sources.

So, given these facts, I think the story is bogus. It is much more
plausible that the auto industry would be able to incorporate a
transponder
into an existing piece of electronics they already put into every car,
that
has a power source, and that already knows your exact speed. Or then
again,
they could take over the entire tire industry to include a sophisticated
electronic device which would be essentially disposible into disposable
tires...







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