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Re: Speed equation

To:, ('')
Subject: Re: Speed equation
Date: Thu, 8 Aug 2002 18:33:21 EDT
In a message dated 08/08/2002 5:17:11 PM Central Daylight Time, writes:

> Actually, both of these equations overstate mileage by about 2-3%,
> depending upon the tire.  The most accurate equations for such (calculating
> speeds or determining pulse rates for electronic speedometers) use the
> rolling circumference of the tire, rather than the calculated
> circumference.  The rolling circumference is dependent upon the length of
> the tire patch at normal pressure, so the larger the footprint of the tire,
> usually the lower the rolling circumference. 

Ah so!  

How does one get a reasonably accurate rolling circumference?  

We've taped tires with a soft tailor's tape to get a circumference, and 
always came up with a number different from one produced with the 
mathematical calculation.  But neither allows for a loaded foot print you say 
comes into play.  

I have to assume the tire and wheel would have to be loaded with the car's 
weight.  So do you mark the side of the tire, lay a tape on the ground 
parallel to the car, and then roll the car forward?



Probably be better if I just went on estimating my speed.  Sometimes I get up 
to 160 then.  I don't think I can do that with these calculations.

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