[Shotimes] weird noise/weird tach/weird speedo

[George Fourchy]

On Fri, 18 Mar 2005 10:57:31 -0500, Jason Hartberger wrote:

>When my speedo says 70, my GPS says 69, which 
>makes sense cos I got a speeding ticket for going 69 in a 55 (my cruise 
>was set to 70), but when I'm going 30, GPS says I'm going 25-26. What's 
>the deal with that? I'm running 225-55-16s on my car... I'm not worried, 
>but could it be bad in the future?

Assuming it isn't binding or wearing out bushings and bearings (or electronic), your
speedometer gives only an approximation of your speed, even in the best conditions. 
It is made up of a magnetic yoke spinning around a disc, which is induced to move by
the magnetic field.  The amount of magnetism can be varied from one speedo to
another, and can be adjusted by a competent speedo shop, which will vary the amount
of movement of the needle at a given speed.

The odometer is mechanically driven by a gear drive coming off the yoke.

In the '60s, I had a 65 Mustang....the yellow one on my website.  I had the speedo
calibrated to read accurately at 140 mph, its top indication, and after that was
done, it read fast at the 60-80 mph range.  We calibrated the car on a dyno at the
shop, so then I could say that when it was going 125, its top speed, it REALLY was
going 125.  Also, I got to cruise at a faster indicated speed than I really was
going on the highway, and so was safer from tickets.

Lexux cars come that way from the factory....5 mph fast at 70, so that their drivers
get less accidental speeding tickets.

George