speedo accuracy

[rapieper@yahoo.com (Ron Pieper)]

I have a speedo that is accurate according to calculations on gear
ratio, wheel/tire diameter, and engine RPM.  Dead accurate, the
correlate to the best my vision can determine.

BUT when I pass one of those portable police radar "Your Speed Is..."
trailers, the speed indicated by the radar is nearly 10% higher than my
speedo and tach/theoretical speed chart would indicate.

I have to assume my calculations AND my speedo are off, or the radar
trailer is off...WTH?


--- Allyn <amalventano@sc.rr.com> wrote:
> > If I thought about it I'm sure I could figure out why speedos
> > are less accurate at higher speeds mathematically but I'm too lazy.
> 
> its due to driven wheel slip % at higher speeds.
> 
> > At first I thought it was the flexibility of the cable making it
> unable to
> keep
> > up with the speed of the vehicle but that energy has to go
> somewhere and
> > eventually it would just twist off everytime you drive
> 
> answered yourself on that one.
> 
> > Probably has to do with the higher tension
> > of the spring on the needle at higher speeds!  HTH
> 
> nope, spring is linear, the tension goes up even from 10-20 mph.
> going from
> 10-20 adds the same tension as going from 100-110.
> 
> Al
> 

=====
Cheapass Ron
'87 Scirocco 16'Victor'

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