George:
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.
Depending on which rear end, which speedo sender and the tires you've got
installed, it might be right and it might be wrong. Regardless, don't
depend on your GPS receiver to provide an accurate speed measurement. GPS
doesn't actually offer any measure of speed, and so the speed calculation is
made by your receiver itself. The accuracy of the reading is totally
dependent on the processing power of the receiver and the design of its
differentiation routines. To get the most accurate reading, you must be
driving at a steady speed for a long time, say, two minutes or so. And even
then, it may not be that accurate.
I'd suggest taking out the old stopwatch and driving at steady speed between
two mileage markers. That will be more accurate.
Rich Wagner
Montrose, CO, USA
'82 GTV6
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