Calibrating VDO/Audi speedometer to compensate for different tire diameter

Ameer Antar
Wed, 31 Jan 2001 14:39:02 -0500

oh ya, about calibrating the speedo, I don't see anything about adjustment 
in my 5k Bbentley. But I think the speedo sensor just outputs a 0-5V signal 
to indicate speed.  So you could adjust this by putting a simple circuit in 
between the sensor and speedo. To reduce the voltage, you can simply use a 
voltage divider [just 2 resistors in series], and to increase the voltage, 
you can use an op-amp w/ a linear gain. The circuits would be real easy to 
build, but setting it up and calibrating would be the hard part.


At 01:49 PM 1/31/2001 , you wrote:
>lowering springs help a lot.  of course with the gearing in that car,
>taller tires shouldn't be a problem.  Sorry, I have no idea how to
>recal. the speedo though...
>"Mark W. Byrum, Jr." wrote:
> >
> > Can VDO/Audi speedometers be calibrated to compensate for different
> > (as opposed to stock) tire diameter?  My '89 80q seems to have a lot
> > of room around the tires in the wheel wells; if a calibration could be
> > done, somewhat larger tires might be installed.
> > Just a thought.
> > TIA,
> > Mark
>Huw Powell