kirbyasmith at gwi.net
Thu Oct 20 16:57:35 EDT 2005
Do you consider the static loaded radius a useful (proper?) means of
calculating revs per mile from which speedometer calibration can be
inferred? The reason I ask is this historical tidbit.
Once upon a time there was a large deck tape recorder series
manufactured by Ampex (which I noticed last week still have a building
in the Valley). The tape speed was determined by a capstan that pinched
the tape between itself and a rubber idler so that tape speed equalled
the surface speed of the capstan. Below the deck the capstan axle was
attached to a steel wheel with a rubber band around it about 1/4 inch
thick. This wheel was driven by a precision diameter metal wheel
attached to the motor. The motor wheel was smaller in diameter than the
capstan wheel by a factor of, say, five. The tape speed could be
tweaked by changing the motor wheel to capstan wheel pressure. The
interesting thing was that if one wanted the tape to go slower, the
pressure was increased, pushing the motor wheel into the capstan drive
wheel, reducing the rolling radius (which one might think would make it
spin faster). What was happening was that the motor wheel had to travel
along the entire circumference of the capstan wheel to generate one
capstan revolution, and this circumference was slighly _lenghtened_ by
distorting the rubber inward.
I have always wondered whether the rolling circumference of a tire is pi
times the loaded radius, or something larger that the tire companies
determine by experiment.
Bruce Schug wrote:
> Here's another figure of interest, especially to Bill who is trying to
> figure hub to wheel opening figures. The static loaded radius for the
> 6.50-13's ranged from 11.1 - 11.5. For 7.00-13's; 11.5 - 11.9 and for
> 7.00-14's 12.1 - 12.2.
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