does anyone know the answer

[cookie]

to this request from an ebay punter? he's talking about the ratio markings on the speedo.

While we're on the subject of speedos, do you have any idea what the "W715" actually represents...? I'm looking for a 'W773" for a fellow enthusiast, and out of curiousity, but I honestly haven't a clue as to what the difference is between these speedos. There's another one on the german ebay site that ends today or tomorrow, but it's a "W747". Haven't managed to find anything in either my Haynes or Clymers' manuals. Thanks for any info.

 

[Le singe]

As most of the speedo cable driving parts seem to be the same,could the numbers relate to the revolutions of the cable the speedometer requires to record a mile?

 

[Vern]

I checked all this out ages ago,and the only thing I could find out was that I couldn't find anything out.Most speedos used to have the gearing on the face,but when I was hunting,all the part no's were the same except for some military spec things
I started because of people changing their wheels for alloys,if you do the sums,it works very much in mbw's favour when it comes to servicing!!!

 

[Steptoe]

The old airheads had different speedos numbers to match the final drives, as the speedo ran from the gearbox .

Oilheads speedos run from the front wheel, and the speedo drives are different ratios/numbers, for whatever model you have -

Are they selling the speedos with the drives ? and are just quoting the drive unit number ?

 

[cookie]

i'm selling an airhead speedo & have received a queery re: W number & what it means.

 

[Le singe]

If you've listened to a German speaking english,you'll know that the W stands for wevolutions.

 

[hops]

You're probably not far away!

If you've listened to a German speaking english,you'll know that the W stands for wevolutions.

Back in the depths of my mind I seem to remember something to do with tachograph calibration and the 'W' does stand for something 'turns'

I think it is the number of pulses for one revolution of the gearbox or something like that anyway!!

 

[Le singe]

Joking aside,'Wicklungsverhaeltnis' means 'turns rate'.
Therefore,the W numbers should relate to this.

 

[Alts]

Ok. If the numbers signify the turn rate..., WHAT, exactly, are they turning? Why the differences between a W715, a W773, and a W737, or whatever other ones that I have yet to come across? Surely there must be some reason why the different speedos are not interchangeable.

I just discovered a little piece called a speedometer pinion or speedmeter drive gear in both my Haynes' and Clymers' manuals; and, after carefully checking the parts cd, it seems as though the part number is the same for all G/S and GS's irregardless of the year.

What is the function of this piece?

Warning!: I understand quickly, but you have to explain a long time.

 

[Le singe]

I'm not familiar with the differences between all the BMW models,but,if you've found the speedometer drives are the same,the number of cable rotations will vary per unit distance because there are differences between different models wheel sizes.
For instance,a 19" wheel will obviously complete less rotations in a mile than an 18" wheel.
As the drives are the same,the difference must be catered for in the speedometer itself.
Could it be,for example,a 19" wheel speedometer cable rotates 773 times whereas an 18" whhel speedometer cable would rotate 793 times,so each wheel would require a speedometer with a W number relating to this?
All the numbers above are given just as an example.

 

[Alts]

So far, so good. I'd thought of the wheel possibility. And to follow that reasoning a bit further (sorry, but I'm new to this), if I were to replace with a different ratio speedo, this should also mean that the actual speed would be incorrect, non? At least within a reasonable limit, as between 773 and 747, for example.

Other question, also: what does the rear drive ratio (i.e. my 37/11) have, if any, on the speedo reading?
This might seem as if it's a silly question, but I'm only at the beginning of my apprentissage.