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 - Vanagon, Transporter and Iltis Sales and Importation - European Lighting for most Volkswagen models -----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. |
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