Speedo reading low?!?

[Steve Sears]

Mike,
It depends on the car, I suppose.  My cable-driven speedo on my 1980 5k is
extremely out of wack - measures around 90 km/h on the highway when I _know_
that the traffic I'm keeping pace with is doing at least 110 km/h.  The
speedo in my 1987 5ktq is electro-mechanical, relying on signals from a gear
in the tranny output - if the gear lost a tooth I guess it would read low.
When brand-new, you are correct that the speedometers intentionally read a
bit over the actual speed for the car, to allow for errors such as slight
different tire rolling diameters, etc.  Maybe the trooper was bored, tired,
out of practice arguing with a driver, needed an ego boost, liked your car,
????  The mile-marker method is a decent way of checking the calibration of
the speedo.
Cheers!
Steve Sears
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
----- Original Message ----- 
> From: Michael McLaughlin <mcloffs at mac.com>
> Subject: Speedo reading low?!?
> To: quattro at audifans.com
> Message-ID: <188bfb4853b307b095213b30d5078a29 at mac.com>
> Content-Type: text/plain; charset=US-ASCII; format=flowed
>
> I got pulled over last night. I was doing a quick round trip between
> home and a town about 75 miles away, on two-lane rural highway with a
> 60 mph limit (for you Northwesterners it was between Pullman, Wash.,
> and Spokane). I'm Mr. Five Over, and had the cruise control set right
> at 65. On the way up I came across a Washington State Patrol cruiser
> heading the other way who didn't seem to be concerned with my speed. On
> the way back, I was also doing 65 and came across a WSP cruiser heading
> the other way again. This time, he turned around and pulled me over.
> Turns out it was the same trooper -- he said he didn't have a chance to
> turn around the other time, and recognized my car coming back (I guess
> Pelican Blue really is distinctive).
>
> Anyway, he told me he clocked me going 70 (both times). I was really
> surprised, of course, and told him I had the cruise control locked in
> at five over. He took my driver's license, was back at his car for
> about a minute, and let me off with a warning and a recommendation to
> slow down a bit.
>
> Finally, I get to my point.  :-)  Is there any chance in heck that my
> speedometer is reading low? It I recall correctly, German speedometers
> tend to read high, and I have stock-size tires. I have a feeling he was
> using a bit of hyperbole to get me to slow down, since if I really was
> going 70 he probably would have ticketed me.
>
> So, what do you think? This is making me a bit paranoid. Next time I
> come across a speedometer check area on the freeway I'm going to time
> it.
>
> Thanks,
> Mike
>
> P.S. He didn't seem too concerned with my lack of front plate, nor my
> illegal window tinting.  :-)