Re: Pathological speedometer

["Mark Battley" <m.battley@domain.elided>]

>I've always had problems with an inaccurate speedometer on my '74 GTV, 
>but was once told to "multiply the tach by 2" to get an estimate of my 
>speed in 5th gear (eg 3500 RPM in 5th gear is about 70 MPH.) 

Leaving aside the tyre size issues that you are already aware of, it will
only be as accurate as your tacho, which in my case I know is LESS accurate
than my speedo. They are both mechanical gauges, working on basically the
same principle, subject to same problems with wear. Both can be
recalibrated.

I'd suggest that you check your speedo calibration, either against "mile
posts" as has already been suggested, or with a hand held GPS. Then you can
work from that.

<I was once told of a proverb that a man with one watch knows what time it 
<is, but a man with two watches is never sure...

Indeed, particularly when both are likely to be wrong!    :-))

Mark Battley
Auckland, New Zealand.

1973 Alfa Romeo 2000 GT Veloce

Alfa Romeo 105 series Bertone Coupe home page and register at:
      http://www.geocities.com/MotorCity/1806/105GTV.HTML

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