In a message dated 08/08/2002 5:17:11 PM Central Daylight Time,
mporter@zianet.com writes:
> Actually, both of these equations overstate mileage by about 23%,
> 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?
Bill
PS
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.
