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RE: Gtech + speedometer error = ???

The Gtech knows absolutely nothing about the cars speedometer. It uses an
accelerometer and time to compute speed and distance. This is also the
greatest source of error. Since the accelerometer can't tell the difference
between horizontal acceleration and vertical (gravity). You must be
absolutely careful to make sure it is perpendicular to gravity and pointed
in the direction you want to measure.   The error comes in when you pop the
clutch and the nose of the car raises and the gtech measures a gravity
vector along with your forward acceleration. Higher priced (much) units,
like the vericom I believe, use three accelerometers and can measure forward
and lateral acceleration as well as correct for deviation from vertical.


> -----Original Message-----
> From: owner-quattro@coimbra.ans.net
> [mailto:owner-quattro@coimbra.ans.net]On Behalf Of Chi Wong
> Sent: Friday, April 09, 1999 12:17 PM
> To: 200q; quattro
> Subject: Gtech + speedometer error = ???
> Just wondering if the recent Gtech results took the
> speedometer errors into account (200q 20v speedos are
> over-optimistic ie 60 indicated = 55 actual, at least
> that's what I understand from reading Chris Miller's
> site).
> The concern here is that if the speedo errors were not
> taken into account, the 0-60 accel times are actually
> 0-55, or am I missing something?