6 replies [Last post]
Wynand
Wynand's picture
 Offline
VBMWMO #7935
Cape Town, South Africa
Joined: 01/15/2011
Posts: 121

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?

__________________

1956 R50
1976 R60/6

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6831
I couldn't find any sources

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?option=com_content&task=view&id=118&...

and interpolate for 3.1818, I get 0.7698. Go figure!!

__________________

Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Daves79x
Daves79x's picture
 Offline
VBMWMO #9030
Joined: 08/09/2015
Posts: 350
Whichever

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

__________________

Dave

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6831
Multiply the 1.2 by 0.621 to

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

Daves79x
Daves79x's picture
 Offline
VBMWMO #9030
Joined: 08/09/2015
Posts: 350
Verified

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

Dave

__________________

Dave

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6831
The W number is an indication

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

Wynand
Wynand's picture
 Offline
VBMWMO #7935
Cape Town, South Africa
Joined: 01/15/2011
Posts: 121
Thanks Kurt and Dave, So I

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.

__________________

1956 R50
1976 R60/6

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.