The speedometer is very easy to re-calibrate. Simply reposition the needle. As for the odometer most from this vintage are over ambitious ~4%. The number at the bottom of the speedometer face indicates revolutions per mile. Compare that with the RPM of the tire size you wish to run. Some vans have speedos calibrated for 805 revolutions per mile and stock tires run close to 830. That 3% right there. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Ralph Meyermann
Sent: Monday, July 28, 2014 9:22 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Crazy idea?

I'm probably not the only one to think of this. With all the various tire sizes/options we are putting on and changing our Speedo readings, I was thinking modification of the O2 mile counter or making something in its place with changeable gears to correct the reading for running non factory size tires???  Do I need medication for this idea??

Velma 82 1.9L AAZ TD Westy