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## Re: Speed equation

 To: mporter@zianet.com, fot@autox.team.net ('fot@autox.team.net') Re: Speed equation BillDentin@aol.com Thu, 8 Aug 2002 18:33:21 EDT
 ```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 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? 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. ```
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