Date:         Fri, 8 May 1998 08:59:16 -0400
Reply-To:     "Lebron, Nathan (GEP, Contractor)" <Nathan.Lebron@GEPEX.GE.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         "Lebron, Nathan (GEP, Contractor)" <Nathan.Lebron@GEPEX.GE.COM>
Subject:      For the mathematicians:  Tires and Speedometer
Comments: To: Vanagon <vanagon@vanagon.com>

I was driving bak home and had my friend follow me to measure the speed.  She
was doing 55 MPH while I was hanging out at about 73 mph.  The last time we
did this, after replacing a bad speedo cable, she was doing 30 while I was
doing about 42 mph.  Considering that there is a certain acceptable margin of
error with speedometers, the discrepency is pretty large.

Now, VW recommends 185/80 R14 for the 85 Vanagon ( as stated on the door
jamb).  Presently I have 205/75 R14.  I understand that the radius is smaller
on the present tires, but would this be responsible for such a large
discrepency?

Another thing, what is the formula for determining the radius and
circumference of a tire given the tire measurements?  I am going to be
replacing the tires and I would like to get light truck tires with the same
meaurements as the 185/80 R14.


Nate El Great
85 GL , 180k mi