Re: [St] Speedometer accuracy

["Joel Ashman" <ashmite@xxxxxxxxx>]

I agree with Mike.  My 2000 ST would show 70MPH on the Speedo and 62 on GPS
units and those radar trailers that the cops use.

And don't worry about the artificial error in GPS.  Mathmatically, it goes
away when traveling in a (relatively) single dimension. In otherwords, if
there is a +/- 100ft margin of error, when you apply to moving in a straight
line, the +100 cancels out the -100 and gives you a 0 average.  So, while
the GPS will be off somewhat for locational (read: targeting) purposes, they
are very accurate for velocity and distance.

Disclosure:  This is all according to the mathematical world of Joel and is
not to be used or trusted for any hard (or soft) science, etc  <grin>.

--Joel

On Mon, Apr 21, 2008 at 3:11 PM, Young, Mike <myoung@xxxxxxxxxxx> wrote:

> The GPS is probably nuts on. Remember that the GPS system is constantly
> measuring minute Doppler effect changes in the timing of signals coming
> from satellites orbiting the earth. You can't go fast enough on the
> surface of the earth to out run a GPS signal. If you held your speed
> constant long enough to read both your speedo and the GPS, your GPS had
> time to update five or six times.
>
> Mike
> '06 ST
> Seattle
>
>
> -----Original Message-----
> From: st-bounces@xxxxxxxxxxxxxxxxxxxx
> [mailto:st-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Kevin Liske
> Sent: Monday, April 21, 2008 11:33 AM
> To: ST@xxxxxxxxxxxxxx
> Subject: [St] Speedometer accuracy
>
> I recently borrowed a Garmin Rino 120 from work to take on a road trip.
> I
> put it on the trip computer settings.
> I had speed, max speed, average speed, odometer, and a few other
> readings.
> It seemed that the Garmin odometer matched the bike odometer very
> closely.
> I did notice that as my speed increased above 50mph, there was an
> increasing
> variance in
> the readings of the bike speedo and the gps speedo.
>
> Bike     GPS
> 40        40
> 50        49
> 60        58
> 70        66
> 80        75
> 90        83
> 100      92
>
> I have two theories.  1)  The bike speedo is actually inaccurate at high
> speed.
> 2)  The bike speedo is correct and this gps can not process the signal
> accurately
> enough to be correct while moving at high speed. (This is a hand unit
> designed for
> people walking around after all and just may not have the specs to
> handle
> high speed.)
>
> Any thoughts?
> --
> Kevin Liske
> `03 Sprint
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