Stock tire size on my '87 was revealed to be reading slow when we borrowed "Samantha" the GPS from neighbors for a trip. �In addition to reminding us about all the turns we'd missed she informed us that at an indicated 65 we are really doing about 58. �Here I thought everyone else was really hauling and it turns out I'm the one who is not.
Stephen

--- On Mon, 5/6/13, Mike Miller <mwmiller6@ATT.NET> wrote:

From: Mike Miller <mwmiller6@ATT.NET>
Subject: Re: speedometer accuracy
To: vanagon@GERRY.VANAGON.COM
Date: Monday, May 6, 2013, 4:54 PM

I'm interested too. I've put 225/75-15 BFGs on and my speedometer is off,
according to my GPS, by more than the percentage the difference in size between
that and stock predict. I thought the stock VW speedometers were off but on the
high side as Karl indicated, but the percentage is greater, meaning the stock
was reading too slow?

Also I have a scan gauge and it indicates about 100 RPM less than the diesel
tach idicates? Which is likely to be more correct and how does each determine
RPM?

Mike in Cotati

________________________________
From: Karl Ploessl <karl.ploessl@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Mon, May 6, 2013 1:29:08 PM
Subject: speedometer accuracy

so I finally got a GPS in my van. And what do I notice?
Speedometer says 60 mph and GPS says 45 mph! At 70 (speedometer) the GPS
says 62!
I am running Michelin Agilis 61 in size 185/14 C and it is a Westy 81
aircooled. And it is in Delaware to satisfy Scott.
The question I have: does this discrepancy also affect the odometer?

------
Karl
1981 Westy "Jenny"
2000 VW Jetta GLS VR6
Wilmington, DE