Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (July 2002, week 1)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Mon, 1 Jul 2002 10:09:32 -0400
Reply-To:     Jay L Snyder <Jay.L.Snyder@USA.DUPONT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jay L Snyder <Jay.L.Snyder@USA.DUPONT.COM>
Subject:      Speedometer/Odometer Calculation
Comments: cc: Rocky.R.Snyder@usa.dupont.com, jfmaurer@juno.com
Content-Type: text/plain; charset=us-ascii

Over the weekend I checked my tachometer reading at 60 mph indicated and it read 3500 rpm. This an '85 4-speed, with the 4.86 ring and pinion and the 0.85 fourth gear. I am running Kirkland 195-75-14 tires, which have a theoretical circumference of 80.16". However, from the Tire Rack website, the same size tires are listed as 816 revs per mile. The speedometer is marked as being calibrated for 805 revs per mile. I have recently checked the odometer using mileage markers over a twenty mile distance and it reads 4% fast. It read 10.4 miles for every 10 miles traveled. If you use the 816 revs per mile figure from Tire Rack, it calculates to a 3.8% error. Which means both my speedometer and odometer are probably both reading 3.8% fast. So 60 mph indicated is really 57.8 mph at 3500 engine rpm. The Bentley lists the allowable speedo error as +3 mph. A true 57.8mph can only read as high as 60.8mph on the speedometer, which means my speedometer is within the specs. The difference between tire revs per mile and the theoretical circumference calculated from the diameter given is curious. I didn't realize the tread contact area and tire bulge affected the "rolling circumference" this much. Do inflation pressures then affect the tire revs per mile?

Jay


Back to: Top of message | Previous page | Main VANAGON page

Please note - During the past 17 years of operation, several gigabytes of Vanagon mail messages have been archived. Searching the entire collection will take up to five minutes to complete. Please be patient!


Return to the archives @ gerry.vanagon.com


The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.

Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.