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Thread: Speed W Numbers and Rear Drive Ratios

  1. #1
    rbleau
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    Speed W Numbers and Rear Drive Ratios

    Hiya - I searched the MOA forum a bit, sorry if I missed a prior post, but I am looking for the list that matches rear drive ratios with "W" numbers in the speedo unit. I have a 1973 R60/5 with a 37/11 rear drive. Not surprisingly, the odometer failed. I read Snowbum's articles, and some ABC tech stuff, and he nicely calculates a theoretical "accurate" ratio - but I am looking for what are the actual W numbers BMW put in the bikes ! Thanks in advance....tough to read the speedo head stamping on the /45 unit but it "looks" like 1.215, assuming the German "1" looks sort of like a funny number "7".

  2. #2
    Liaison 20774's Avatar
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    This discussion by Snowbum?

    http://bmwmotorcycletech.info/ringgears.htm

    Not surprisingly, the odometer failed.
    What do you mean by that? Having any given speedometer hooked to a bike, even if it is the wrong ratio, doesn't necessarily mean it's going to fail.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Registered User lmo1131's Avatar
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    even if it is the wrong ratio, doesn't necessarily mean it's going to fail.
    And . .. . according to the guys at Palo Alto Speedo, the intermittent shock loads caused by a bunged-up drive cable can cause instrument failure...

    They're old instruments. I just had mine rebuilt too.

    the German "1" looks sort of like a funny number "7".
    Hence the reason for the slash...

    "It is what you discover, after you know it all, that counts." _ John Wooden
    Lew Morris
    1973 R75/5 - original owner
    1963 Dnepr

  4. #4
    Liaison 20774's Avatar
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    Quote Originally Posted by Lmo1131 View Post
    And . .. . according to the guys at Palo Alto Speedo, the intermittent shock loads caused by a bunged-up drive cable can cause instrument failure...
    I agree with some malfunctioning equipment. But the OP seemed to suggest that running a rear drive not compatible to the speedometer ratio would cause it to fail. Even it were the correct ratio, a bad cable can still break something.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
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    If that is an original (unmodified) speedometer, it should have a W1244 (1.244 on snowbums article) code if it is in miles per hour and calibrated for 3.36:1 findal drive ratio. That indicates the input cable turns 1244 revs per mile.
    BMWs in my garage: 1982 R65LS, 1978 R100/7

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