"W" markings on speedo

[Mike Arman]

On 7/28/2012 4:36 PM, Cody Forbes wrote:
> That seems odd in this instance. Haven't we seen like 4 different W numbers for cars with the
> same final drive?
>


Could be. Tire size makes a difference (not a big one), what's in the parts bins sometimes does, and 
what's available in the parts yard might, too. I can say though, that for BMW motorcycles 1950 
through 1969, the W number on the VDO speedometer definitely codes across to match the final drive 
ratio - every time. It is stamped on the back of the speedo, and printed on the face. The final 
drive ratio is stamped into the aluminum drive housing.

In fact, when converting to sidecar use, you are supposed to change the final drive (yeah, right, 
anyone find out what that costs?) and the workshop manual cautions you to change the speedometer to 
one with the correct W number as well so the reading will be accurate.

Hollywood Speedometer and Clock used to fix these (they still may) and they *always* asked for the W 
number and the final drive ratio. These bike used a mechanical speedo, driven by a conventional 
cable, not some fancy, expen$ive electronic device.

Best,

Mike




> -Cody Forbes
>
> On Jul 28, 2012, at 3:08 PM, Mike Arman <Armanmik at earthlink.net> wrote:
>
>>
>>
>> The "W" marking (a number) on the speedo indicates which final drive ratio that speedo should
>> be used with to get a correct indication.
>>
>> When I was fooling with BMW motorcycles (vintages 1950 through 1969), I made a list of the W
>> numbers and the final drive ratios they matched up to. Similar lists are floating around the
>> internet.
>>
>> For instance, a W=1.2 goes to a 27/8 final drive, and the indicated speed will then be accurate
>> (or as accurate as can be expected). Those numbers may not be correct, it has been a few years,
>> but that's what they are for.
>>
>> Best Regards,
>>
>> Mike Arman 90V8Q and a bunch of old BMW bikes _______________________________________________
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