RE: Trail Mileage and GPS and bikes

["Salim Nice" <snice@hcrecovery.com>]

If you want to get an accurate GPS reading you need to buy the external
antenna if you have a Garmin.  The price is about $100 at West Marine and
you need to be sure it is not the extension cord for the existing antenna.
The one I am talking about looks like a little computer mouse only much
smaller and does a much better job of acquiring and locking onto satellites.

Salim Nice

> -----Original Message-----
> From: Ed & Wendy Hauser [mailto:sisufarm@mmmpcc.org]
> Sent: Wednesday, August 23, 2000 2:35 PM
> To: Ridecamp
> Subject: RC: Trail Milage and GPS and bikes
>
>
> I just got back from riding my odometer equipped bike on a "20"
> mile loop of
> my ride.  These trails have been used for many years, but I have
> always felt
> that they were "short"
>
> I bought a new odometer and calibrated it per the manufacturers
> instructions.  I then rode it on a measured course and got
> agreement to the
> 0.01 mile over 1.5 miles.  I think this is as good as it gets.
> This morning
> I went to the park with my bike and GPS.  I was hopeful that with the
> "selective availability" turned off, the odometer on the GPS would work
> well.  As these trails are along the beautiful St. Croix River, they are
> very flat, so no problems with elevation changes should happen.
> Much of the
> mileage is wooded however.   At this season, the leaves may screen the
> signal.  My results were quite interesting.  I carefully avoided using the
> front brake, and steered as straight down the trails as possible.  I did
> have to zig-zag at times, so my bike mileage should be on the high side.
>
> In the past my GPS has seemed to understate the mileage by about 10%.  Now
> on the first half of the loop the bike said 9.49 miles, and the GPS said
> 9.15 miles.  An error of -3.6%.  Not bad.
>
> Things got interesting on the way back.  On one section (which was going
> over the same trail in the opposite direction) the bike said 5.08
> miles but
> the GPS said 6.98 miles!   By the end of the loop the GPS said I had gone
> 19.71 miles, but the bike said 18.73 miles.  For a difference of +5.2%.
>
> My conclusion is that while things are better now, my GPS does strange
> things with mileage every once in a while.  The accuracy is certainly good
> enough for training rides, but if using it to measure a distance ride one
> should double check for strange things.  I don't know why my GPS messes up
> mileage, because it always locates my position with great precision.
>
> By the way if anyone is going to be in MN Sept 16,17 come to Sisu-Sisu.  I
> can at least guarantee accurately measured trails, and a spaghetti dinner.
> (an email would get a ride flyer).
>
> Ed and Wendy Hauser
> 1140 37th St.
> Hudson, WI 54016
> sisufarm@mmmpcc.org
>
>
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