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Rolling diameter and new numbers

To: <tigers@Autox.Team.Net>
Subject: Rolling diameter and new numbers
From: "Dave Binkley" <dbinkley@cox.net>
Date: Wed, 15 Dec 2004 20:23:49 -0700
That's a good suggestion to measure the rolling circumference and then
calculate the diameter.  It does indeed come out different.   After doing
the mark, roll, mark and measure routine in the driveway I came in with the
raw data, fired up the PDP-11 and wrote a Forth program to perform the
calculations prescribed by Steve.  Yesterday I reported the diameter to be
22.64, but today I am reporting that the actual rolling diameter is 21.76.
The difference of .88 inch smaller is enough to make my tach error worse by
about 100 for a total error of 500 rpm too low in the 60 - 70 mph range.  

Dave





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