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Speedo to match final drive 35:11

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Wynand
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Speedo to match final drive 35:11

Post by Wynand »

Would appreciate if someone can confirm the stock speedometer that goes with a final drive ratio of 35:11

This is for a R50 1956 of the which the final drive is 35:11 and correct according to a couple of sources.

Veigel or VDO, but what ratio? 0,95?

And would the right one be available in km/h or only mph?
R50, R60/6, R90s

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schrader7032
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I couldn't find any sources

Post by schrader7032 »

I couldn't find any sources that list that specific final drive for the R50. Other sources that list speedometer ratios for given final drives also didn't show the 35/11. But looking at what Snowbum has on this page:

http://bmwmotorcycletech.info/ringgears.htm

there is a direct relationship between the final drive and speedometer in order for the speedometer to read correctly. 35/11 equals 3.1818 and in looking at his chart, the ratio 3.1818 falls 3.09 and 3.2. By interpolating on the W numbers for these two, I come up with 0.7327. Don't know if such a speedo exists, but that's what it should be.

If I look at the numbers at the towards the bottom which Snowbum specifies for /2 bikes, he has limited information. I took the values for 35/8 and 32/7 and extrapolated back to 35/11 (3.1818), I get 0.7956. So, I'm not sure which W numbers are correct...probably the 0.795.

If I use the numbers on this page:

http://bmwvmca.org/joomla/index.php?opt ... &Itemid=37

and interpolate for 3.1818, I get 0.7698. Go figure!!
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Daves79x
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Whichever

Post by Daves79x »

Which ever KM ratio that's equivalent to 1.2 in MPH would be correct. My 35/11 final drive has a matching 1.2 speedo, in MPH. Those should be pretty common.

Dave
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schrader7032
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Multiply the 1.2 by 0.621 to

Post by schrader7032 »

Multiply the 1.2 by 0.621 to convert to KPH. That would be 0.745.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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Verified

Post by Daves79x »

Yes, just verified the KM ratio would be .75. New ones are still available in KM from S Meyer.

Dave
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The W number is an indication

Post by schrader7032 »

The W number is an indication of how many turns the speedometer cable makes per mile (or kilometer). So a 1.2 means it turns 1200 times in one mile. So one could do some tests by putting a paper clip on the end of the cable and rolling the tire through one exact revolution. That way you can figure out exactly what is needed. Palo Alto Speedometer has a form describing the process:

http://www.paspeedo.com/ratio.htm
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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Wynand
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Thanks Kurt and Dave, So I

Post by Wynand »

Thanks Kurt and Dave,

So I confirm speedo with ratio 1.2 for mph and 0.75 for kph. Seems to be part number 62128080076 that would match this final drive of 35:11 and give a true speed reading.

Quoting from Slabon's book, page 106: "Solo gears for the R50, R60 and R69 were first 11/35; that is, eleven finely cut teeth... After 1961, the gears were changed to 25/8, which was also used on the R69S"

Especially appreciate the calculations Kurt. Always nice to know the answer is backed up by the maths.



R50, R60/6, R90s

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