[T3] Speedometer/Odometer ratio?

[Jim Adney]

I believe that all US cars have speedometers that expect 100 
revolutions of the speedometer cable per mile of distance traveled. 
To get this right, appropriate speedometer drive gears are installed 
in the vehicle transmission at the factory, and the speedometer cable 
gets its drive from a special connection on the side of the 
transmission.

VDO does this differently. On the back of every VDO speedometer there 
is a stamped number which I believe is the ratio that makes this 
speedometer/odometer correct for this car and tires. All the Type 3 
speedometers I've ever seen, which get their drive directly from the 
front wheel, have either W0.80 or W0.82 stamped there. I assume the 
small change might have come with the introduction of radial tires, 
or it's possible that VW just made a minor correction at some time. I 
really haven't noticed whether this was a change that happened at one 
particular time or if they started getting mixed at some point.

I also have a VDO speedo out of a Mercedes, and that is marked W1.47. 
Those cars got their drive from the transmission.

So here's my question: What does the W0.82 mean? (I just measured the 
diameter of my tires, and they are about 0.65 m. Not even close to 
0.82.)

Does anyone know what this means?

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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