re: speedometer error

[Jay Negrin <jmnegrin@domain.elided>]

Mitch commented/asked:

<<For lack of better company, I took my GPS for a ride in my '74 spider
to  check the speedometer.  I was surprised to find it indicating about
12% BELOW  actual speed.
Every other Alfa I've been associated with ('67 and '74 GTV's) all were
optimistic by at least 10%. They all have/had stock tires and wheels.

I'm curious as to what the range is, and thought it would make a good
rainy  day thread. Has anyone else checked their Speedo vs. an accurate
car, GPS, or  police radar gun (intentionally or otherwise)? >>

I've had the Alfetta on the open road to the track (just for visiting
our club member in competition, you understand), and at least here in So
Cal, the highway dept, or who ever, has been nice enough to put paddle
markers with mileages on them every mile or so.  In addition to that,
they have put markers with mileage on many overpasses and bridges.
Those are usually posted to the nearest 0.01 mile.

At a true 60 mph, it takes 1.00 minutes to go one mile.  If your clock
measures 10% less than that, you travelled the mile 10% faster, or 66
mph.  10% more time means 10% slower, or 54 mph.  For what it's worth,
my Alfetta comes up reading fast.  Indicated 70 mp really is about 66
mph, according to calcs.

And, the markers are there day and night, day after day, month after
month.  You do not need police rader (thank you, Officer Judy) to tell
you just how fast he thinks you were going.  Ain't that a relief?!

Jay Negrin
76 Alfetta GT
ARO So Cal --- Alfiesta coming to Southernn California, July 4-7, 2002

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