Date: Tue, 2 Jul 2002 21:28:40 -0700
Reply-To: David Marshall <vanagon@VOLKSWAGEN.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Marshall <vanagon@VOLKSWAGEN.ORG>
Subject: Re: GPS to check Speedo
In-Reply-To: <000001c22230$7e750cd0$ac2579a5@LorenLaptop>
Content-Type: text/plain; charset="US-ASCII"
I think you should be stating that you should be careful for using a GPS for
an odometer for the 'as the crow flies' errors. The speedometer is pretty
accurate unless you are drastically changing your direction within one
second. My Garmin GPS II+ is VERY accurate as a speedometer.
Also, taking a stop watch and cruising at 60 MPH for 60 seconds is
impossible - you CAN'T drive a constant 60 MPH for 60 seconds you will
deviate from the 60MPH by a few percent and this will throw your
calculations off.
In Alberta there are many measured kilometers that last for about 6 to 7
kilometers and my GPS is spot on - the odometer is a joke!
David Marshall
Fast Forward Automotive Inc.
4356 Quesnel Hixon Road
Quesnel BC Canada V2J 6Z3
http://www.fastforward.ca mailto:sales@fastforward.ca
Phone: (250) 992 7775 FAX: (250) 992 1160
- Vanagon Accessories and Engine Conversions
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-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf
Of Loren A. Busch
Sent: July 2, 2002 6:25 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: GPS to check Speedo
Be careful before you rely on your GPS to check your speedometer.
Depending on the make and model of GPS, you may be getting distance as
'the crow flies', NOT actual road distance. Not a problem if traveling
on a straight road for the testing, but a problem if any curves in the
road. Set a course into your GPS, then start down the highway in any
direction. The 'distance and bearing" to the next waypoint will be
shown as if you could drive a straight line to the waypoint. Most of
the earlier handheld GPS receivers were developed with boaters in mind,
and make the assumption that you are going in a straight line. More
recent models are designed with the hiker in mind, and some are set up
specifically for use on the road. Figure out how yours' is set up
before coming to any important conclusions. The best bet is still the
measured 5 mile stretches on the highway, just take your stop watch,
cruise at 60 to make the calculations easy, time the 5 miles, note the
reading on the trip odometer at start and end, and back into a
correction. I end up .2 of a mile long in 10 miles on the odometer, and
about 1 to 2 miles fast indicated speed on the speedometer on my '90
Westy running Michelin 185/14 Agilis.
