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Re: Speedometer Accuracy

Over the past two years I've had several different Garmin GPS models, and 
have used them on several bikes. Three of my bikes have calibrated bicycle 
speedometers installed. The GPS speed indications and the bicycle 
speedometers have always been in agreement when I compared them. I often get 
bored when I drive a cage, so I play with my GPS a lot and have checked my 
speed using the stopwatch function in my wrist chronograph to time the 
passage of mile markers. Again, the chronograph and the GPS agreed. I don't 
know if the US Government can fudge the GPS speed info, but other than 
something happening along those lines, I believe we can use GPS as a very 
reliable and very accurate speedometer.

- ----- Original Message ----- 
From: "Pete and Nat Lavengood" <laveng@xxxxxxxx>
To: <oilheads@xxxxxxxxx>
Sent: Friday, June 03, 2005 10:50 AM
Subject: Re: Speedometer Accuracy

>I also use a GPS and the bicycle speedo and they agree and I believe they 
>are accurate.  Pete
> ----- Original Message ----- 
> From: "Bob Hadden" <kbhadden@xxxxxxxxxxx>
> To: <oilheads@xxxxxxxxx>
> Sent: Thursday, June 02, 2005 4:17 PM
> Subject: Re: Speedometer Accuracy
>> Pete,  I have done just that on my new GS.  Haven't found a way to 
>> confirm the accuracy of the bike speedo yet, but it reads about 2 mph 
>> below the bike speedo.  I was very surprised at that.
>> If one has GPS on the bike, is the speed display super accurate at any 
>> given moment?
>> Bob Hadden '05R12GS, '62R27
>> On Jun 2, 2005, at 8:48 AM, Pete and Nat Lavengood wrote:
>>> BMW Designs the speedos to read high. The intent is for the speedo to 
>>> always read high even with the largest possible tire mounted on the 
>>> front rim. They will not recalibrate as it is supposed to be this way. 
>>> Inexpensive and accurate solution is to get a bicycle speedo using a 
>>> magnetic pick-up mounted on the brake disc. This unit is calibrated to 
>>> to the tire on your bike. ie mark a spot on the tire and the pavement, 
>>> roll ten times and measure the distance between spots and divide by 10. 
>>> This is an accurate circumference of the loaded tire and is entered into 
>>> the bicycle speedo to calibrate it to your bike.
>>> From: "Gregory Appling" <gappling@xxxxxxxxxxxxxx>
>>> To: <oilheads@xxxxxxxxx>
>>> Sent: Wednesday, June 01, 2005 10:32 AM
>>> Subject: Speedometer Accuracy