The GPS SHOULD be much more accurate than any other kind of
speedometer. After all, if it can pinpoint where you are within a few
yards, it should be able to figure out how fast you're going within a
very small margin of error.
George Graves
'86 GTV-6 3.0 'S'
On Nov 10, 2009, at 4:52 PM, Will Owen wrote:
Brian Shorey reports:
"OK, My GTV-6 speedo says 80 MPH @ ~3600 RPM which is consistent
with the 22.14 MPH/1000 rpm (which is what the specs on the GTV-6
says as well). BUT my GPS receiver tells me that when my speedo says
that I am doing 80 MPH, and the tach says ~3600 rpm, I'm actually
doing only 72 MPH."
Inneresting. My Milano ('87 Gold) has not had a working speedometer
for ten years, as of this very weekend (no celebrations planned), so
for all this time I've been using the tach as my speedo. Second
through fourth gears I figured out by driving past one of those
radar trailers the cops set up so you'll see how badly you're
speeding and be shamed into slowing down. I'd come up with 10, 14
and 18 mph/1K respectively. I remembered my old Berlina was geared
exactly like that, and that its fifth gear was pretty much 22 per
thou, so I assumed this was the same, and drove accordingly,
including across the country. Lately I've been using my Garmin as my
speedo in that car, and have discovered that the speeds are more
like 10, 15, 20 and 24! Doesn't seem like such a big difference, but
while 66 mph on the Interstate is always OK, just-shy-of-75 often is
not... and that 75 I thought I was driving around here is a tad over
80.
Unless you've got a stump-puller ratio in your car, Brian, I'd think
twice about taking your GPS's word for it!
Will Owen
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