Fred Cisin cisin at xenosoft.com
Wed Dec 2 10:06:18 CST 2015

On Wed, 2 Dec 2015, Paul Koning wrote:
> Actually, it's the circumference that matters, not the diameter.

I always thought that there was a relatively stable relationship between 
those!  :-)
Circumference tends to be a little over 3 times the diameter (3.0 in some 
states)    :-)

> Does the circumference of a rubber roll change significantly when you 
> press on it?
If it shifts or squeezes out to the sides, not so much.
If it compresses, yes.

Before TPMS, some cars got a crude estimation of low tire pressure by 
comparing the RPM of a tire (ABS sensors) with its fully inflated 
(circumference changing with pressure change)

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