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[Phys-l] Real Tire Data



I think we were sometimes talking past each other in the tire
discussion. I also think some people have been writing without going
out and looking at real tires. I went out yesterday afternoon and took
photographs of real tires on real cars. I also photographed my 2004
Honda Accord EXL both jacked off the ground and on the ground. I
analyzed the high-resolution photographs with Photoshop CS3 Extended
which has excellent tools for determining distances, angles, areas, etc.
from calibrated photographs.

The data really turned out nice, which I say partly because it did, and
partly because it turned out just as I expected.

The photographs of the wheel/tire, if you want to analyze them yourself,
can be obtained from...

www.bluffton.edu/~edmistonm/AccordTireOffGround.jpg

www.bluffton.edu/~edmistonm/AccordTireOnGround.jpg

My analysis of these pictures (and the pixel-to-centimeter calibration
data) can be found in the pdf file (acrobat file) below. If you only
download one of the four files in this email message, open the pdf file.
This is where I spent a couple hours of analysis...

www.bluffton.edu/~edmistonm/TireSidewalls1.pdf

I also took photographs of different styles of tires, and I also have
head-on shots so you can see the profiles. The bulge profile is mostly
different than many people have been describing. I still believe I drew
it pretty accurately on the PDF file I referenced earlier. I mostly do
not see the changing angles near the bead that people have talked about.
Tire designers do not design a tire to flex much in the bead region.
The bulge is much lower (away from the bead and closer to the road).
Although I haven't analyzed the profile data yet, and plan to make more
analysis and photos available as I have time, I am now making available
the profile photo of my Accord. This photo is available at...

www.bluffton.edu/~edmistonm/AccordTireProfile.jpg

In this photo notice that the bulge is quite small and very low. I am
using my car jack as a pointer. The screw on the jack is pointing to
the outermost rim. Notice that the bulge area is way below the rim
edge, and the bead itself is another centimeter higher than that. In
the bead area I don't see any change in angle of the sidewall from when
the car is off the ground versus on the ground.

The photographs are each roughly 1.5 Mbyte files. If you don't want to
take the time to download them, at least look at the data in the PDF
file. It think these data are very revealing.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu