Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (January 2001, week 5)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Wed, 31 Jan 2001 03:46:14 EST
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: What I Found About Tire Height Calculations
Comments: To: derekdrew@rcn.com
Content-Type: text/plain; charset="US-ASCII"

Derek,

Just a few additional comments. For my application, 2wd Westfalia, 15 inch Ronal alloys, I concluded that the Yokohama Geolander AT+ 215/75R15C tires were the largest I could fit. These gave a revs/mile number of 755. This compares to the stock reinforced 185R14 r/m rating of 836. This reduces the engine revs per mile (or the effective gearing) by 10.7%. My 5.87 rear axle becomes 5.30 effectively.

Compared to the 235/75R15C Geolander AT+ at 723 r/m, it seemed a good compromise.

Note that the rev/mole numbers are measured with about 3 significant figure accuracy. If you examine the Yokohama tire catalog for the various light truck tires available in the 30-9.50x15 size you will find numbers such as 705, 709 and 704 for different sidewall and tread designs. Within the Yokohama brand group, the 235/75R15 tire has r/m numbers varying from 723 to 744.

These numbers are also strongly related to sidewall strength, as shown on the Dunlop Tire page. Compare the Dunlop P235/75R15 (passenger tire) with r/m of 753 to the LT235/75R15 (light truck tire) with r/m of 744 (Radial Rover AT) or 741 for the Radial Rover RV.

Finally, as has been pointed out before, at the bottom of the speedometer, VDO has marked the calibration point of the unit in revs/mile (US deliveries). On my 82, this calibration point is 805 revs/mile. In my measurements, this has proven to be correct to within 0.6%. For the pathologically inclined, I connected the speedometer cable to an electrically encoded calibrated motor. I found 60 mph indicated on the speedometer 801 shaft rotations per minute (801 revs/minute, or 1 mile per minute and 60 miles per hour). Most people report dead accurate speedometers when running 27-8.50R14C tires (rated at 795 revs/mile as Dunlop Radial Rover RV's, and 801 for the BF Goodrich Comp T/A). Unfortunately the range of revs / mile for the 27-8.50R14C tire varies from 785 to 831 for the range of available brands.

During my 14 inch wheel period, I found the BFG's to be superb and dead on!

I should also mention that there are excellent videos with a strobe camera showing the flexure of the tire sidewall and profile while moving at speed on a regular surface, while cornering, while braking and while running over rougher terrain. Frankly, I'm amazed that they work at all!

Good luck on further calculations,

Frank Grunthaner


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.