Fred Cisin cisin at xenosoft.com
Wed Dec 2 11:55:16 CST 2015

On Wed, 2 Dec 2015, Paul Koning wrote:
> I'm sorry for stirring up this hornet's nest.

Well, I put "emoticons" in, in a futile attempt to indicate that I was 
joking. ("emoticon captioned for the humo[u]r impaired") I also hoped that 
the "in some states" would give a further hint to that.  I couldn't resist 
the humour opportunity, but I did not intend it to be nasty - it is a 
reasonable question.
And, without feeling hurt, I can always count on y'all to catch me up on 
inaccuracies!  :-)

> I actually meant to ask a real question, and the way I phrased it made a 
> mess of things.  The real question: for rubber rollers in this sort of 
> application, does the distortion that occurs significantly affect the 
> circumference?  Or is the nature of the material such that it's squished 
> out of shape, but circumference does not change much?

The question can remain partially inconclusive.  If the rubber is shifting 
without compression, such as if the ID was too large, then the 
circumference could be partially unaffected, but then the circumference 
times the RPM of the axis of the roller is no longer the sole determinant 
of tape motion.

Compression will have an effect on EFFECTIVE circumference (the amount the 
tape gets moved, not the actual measurement around the roller) and remains 
PI times twice the [compressed] radius of the circular segment at the 
area of contact.
Try to IGNORE the other side of the roller that is not compressed, or 
imagine if the entire roller were equally compressed, not just the 
contact patch.
That's why I included the explicit example where tire pressure change 
is/was detected by ABS speed sensors (now often done more directly with 

Here's a similar, but off-topic, one to contemplate:  If kids have helium 
balloons floating against the ceiling of the backseat of your car, which 
direction do the balloons move when you go around a tight corner?

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