Vintage BMW Motorcycle Owners

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?

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!!

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

Multiply the 1.2 by 0.621 to convert to KPH. That would be 0.745.

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

Dave

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

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.