Date:         Wed, 12 Aug 1998 09:06:10 EDT
Reply-To:     DAPrescott@AOL.COM
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         DAPrescott@AOL.COM
Subject:      What Bentley says Re: Speedo calibration (longish)
Comments: To: rubatoguy@WORLDNET.ATT.NET, Vanagon@VANAGON.COM
Content-type: text/plain; charset=US-ASCII

In a message dated 98-08-12 05:43:30 EDT, you write:

> If you look in the Bently manual it states (somewhere) that the speedo is
>  purposly set to read about 5% below actual speed in order to meet us DOT
> laws.  It also explains the number stamped below the VDO.

Todd et al:

Bentley page 90.30 reads as follows:

As of  May of 1983 the existing regulations (FMVSS 127) concerning vehicle
speed indication were cancelled by the Department of Transportation (DOT).
Starting May 1983, the only requirement is that the vehicle's speedometer
indicate a higher speed than is actually being driven.
Speedometers having European calibration specifications were installed in
vehicles for models years 1984 through 1985 (until December 1984 production).
These speedometer heads have a basic tolerance of (+) 6.2 miles per hour with
an additional (+) 5% of the actual speed driven.

For example

     Actual Speed          50 miles per hour
     + Basic Tolerance   6.2
     + 5% of Actual        2.5
____________________________________
Max. indicated speed:  58.7 miles per hour

Speedometers with the former FMVSS 127 calibration are installed starting with
December 1984 production. These speedometer heads have a tolerance of (+) 3
miles per hour.

For example
      Actual Speed         50 miles per hour
     + Basic Tolerance   3
___________________________________
Max. indicated speed   53 miles per hour

Bentley also note on the same page (under the Odometer heading) that:

The number printed on the speedometer face plate beneath the word MPH shows
the number of revolutions required by the speedometer cable mulitplied by 100
to travel a distance of 1/100th of a mile (52 feet, 9.5 inches)

>  The question is if using the number to calibrate still means that the speeo
>  will read 5% slow?

The speedo will, it appears, read as much as 6.2 MPH slow PLUS  another 5%
slow, whatever you do.  This explains why on our last camping trip we were
going 75 MPH (indicated) and getting passed by just about everybody!
I calculate an actual speed of as little as 62 MPH.  BTW, the speed limit was
65, in case you wondered.

The number (805 on mine) appears to give actual distance travelled, reassuring
us that the odometer is reasonably accurate.  Bentley says (-) 1% to (+)
3.75%.  I don't think it bears on speed at all.

Doug