speedometer error

[AlfaNeely@domain.elided]

       I found it interesting that people were spending all kinds of money 
for GPS systems just to test their speedometers.  It sounds like they are 
saying "I have more toys than you do."
       Checking speedometer error is easy by timing mileage markers on the 
highway, or at least on all interstate highways nationwide.  As Jay said, 60 
mph is 60 seconds.  Rather than trying to figure a proportion from that, just 
divide your speed in mph into 3600 to get seconds per mile.  Or divide 3600 
by seconds per mile to get speed.  I could send anyone who wants it the 
actual formula, which is an inverse proportional relationship.  Doing mental 
long division does give you something to do on a boring interstate.
       I try to check my speedometer error as soon as possible after buying 
new tires.  Then, I check my speedometer error periodically as the tires 
wear.  I time several different mileage markers to compensate for hills, 
other traffic and the fact that I am never sure the guys who planted the 
markers were really into doing a proper job.

       I don't need no stinking GPS, I got a map and a magnifying glass so I 
can read it!

Ciao,
Russ Neely
Oklahoma City




In a message dated 01/29/2002 12:36:55 AM Central Standard Time, 
owner-alfa-digest@domain.elided writes:


> 
> Date: Mon, 28 Jan 2002 21:27:18 -0800
> From: Jay Negrin <jmnegrin@domain.elided>
> Subject: re: speedometer error
> 
> 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.
> 
<snip>
 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.
> 
> 

<snip>

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

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