Xref: utzoo sci.physics:4628 sci.electronics:4069 rec.autos.tech:4800
Path: utzoo!utgpu!bnr-vpa!bnr-di!leibniz!keithh
From: keithh@leibniz.UUCP (Keith Hanlan)
Newsgroups: sci.physics,sci.electronics,rec.autos.tech
Subject: Re: Speedometers was: (Can 31 party balloons aggravate 1 police RADAR?
Message-ID: <178@leibniz.UUCP>
Date: 12 Oct 88 21:02:58 GMT
References: <880928.0208.11468@ontmoh.UUCP> <171@leibniz.UUCP> <3010@mtuxo.att.com>
Reply-To: keithh@leibniz.UUCP (Keith Hanlan)
Distribution: na
Organization: Bell-Northern Research, Ottawa, Canada
Lines: 32

In article <3010@mtuxo.att.com> gv@mtuxo.att.com (52341-G.VALENTINI) writes:
>In article <171@leibniz.UUCP>, keithh@leibniz.UUCP (Keith Hanlan) writes:
>> Peter, typically the speedometer lags behind the true speed of the
>> vehicle. If you had just turned the corner and finished accelerating
>> and your speedo read 70, with error, it is not unreasonable to guess
>> that you were really doing 88. 
>> 
>I don't agree.
>
>Typically the manufacturers set the speedometers
>to read HIGHER than what you are actually going. 
>...
>                                      George Valentini

Sorry, I guess I didn't make myself clear. By "lag behind", I meant
the speedometer's reading, *UNDER ACCELERATION*, is inaccurate. Once
the car's speed stabalizes (0 delta-v), the speedometer "catches up"
and becomes accurate. Note that "catches up" and "becomes" are not
instantanious. Thus for "finished accelerating" read "*just*
stopped accelerating". 

I hope that this clarifies the issue.

On the subject of speedmeter inaccuracies, I agree that most read
high (most notoriously Ferraris). My posting did not mean to imply
anything on this topic. Both my car's and my bike's speedometers have
been calibrated dead-on though so I wouldn't get in the habit of 
correcting your speedometer as you drive. ("But officer, I assumed that
my speedo was 5% fast and that you wouldn't mind +15% so I tried to keep
it at 120 in the 100 zone...")

Keith