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RE: Speed equation

To: fot@autox.team.net
Subject: RE: Speed equation
From: "Barr, Scott" <sbarr@mccarty-law.com>
Date: Fri, 9 Aug 2002 11:16:14 -0500
Bill's process is the same as what we use when calibrating the computers on
our racing bicycles.  But in centimeters.  It works very well in that case.

Scott Barr
sbarr@mccarty-law.com <mailto:sbarr@mccarty-law.com>
(920) 766-4693
(920) 766-4756 (fax)


-----Original Message-----
From: Bill Sohl [mailto:billsohl@mindspring.com]
Sent: Friday, August 09, 2002 10:52 AM
To: Mark J Bradakis; fot@autox.team.net
Subject: Re: Speed equation


Mark wrote:
> Getting an accurate tire rolling diameter can be tricky.  For instance, if
> one were to measure the outside edge of the driver's side front tire of my
> '87 Civic Si, you'd get a distance a good inch or two larger than the same
> measurement taken on the inside edge.

I'd offer the best way to get as near a true rolling diameter would be
the following:

1. Mark a point on one of the tires (front or rear depending on
which is the powered wheels).

2. On a flat area (parking lot), bring the car to a stop so the marking
on the tire is at the bottom of the tire (180 degrees) and, therefore,
directly adjacent to the pavement.

3. Mark the pavement where the tire marking is.

4. Drive the vehicle forward so the tire has gone through 10
complete revolutions and stop the vehicle with the tire
marking again at 180 degrees (i.e. next to the pavement.)

5. Measure the overall distance from the starting point as marked on
the pavement in step 3 to the end point and then divide by 10.

The reason for doing 10 revolutions is to get greater accuracy
and granularity to the final calculated result while also minimizing
any pavement imperfiections/variables if you only directly measure
one full wheel rotation against the pavement.

Cheers,
Bill

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