Speedo question

[grumpyone]

Hi folks
Got the R80 (1986) finally running respectable and now have only small this and thats to take care and the first on the list is the speedo. It registers about 20 to 25 mph to fast.
I fail to have a clue where to start if it were a normal situation like a car and mech speedo I would say the gear was replaced with the wrong ratio one in the transmission???
The OD is accurate and dead on wtih our car and the highway markers over a 30 mile test.
The speedo does not seem to have a lot of jumping or vibration in the needle either.
Any tips on this would be much appreciated.
All your help has been very useful in the past and we thank you.
Thanks
Jim and Esther

[20774]

Jim -

BMW speedos were notoriously optimistic...actually there's a bullentin out which identifies how much they can be off, ie, reads high. I've heard that the 85mph speedos were more accurate.

Part of it will have to do with the size tire you're running. But from what you're reporting, it sounds like you have a mismatch between your final drive ratio and the ratio of the speedometer. There's a table in this website:

http://bmwmotorcycletech.info/ringgears.htm

which identifies which FDs went with which speedos. The ratio on the speedometer is in small numbers below the dial.

Beyond that, you could send it out for repair. You could install a GPS for use or use one to calibrate the speedo. Or you could run down a 5-mile stretch of a freeway while holding a steady speed and noting the time to cover the distance. After doing the math, you can compare the computed average speed with what was showing on the speedo. Then you just remember this approximate delta whenever you running down the road.

[fishd4]

The speedometer on my R100/7 was very SLOW. It read about 12mph slower than speed as per GPS. First time I was on interstate with it I felt like I was going much faster than indicated. Riding buddy confirmed at next stop.

With your odometer being correct, I would doubt that the ratio is wrong.

I used the following link http://www.ibmwr.org/otech/speedo.html to take mine apart and look at it. Moved the little brass piece a little and reassembled. Now it was too slow. After several times apart and back together, it now is within 1mph of my GPS. There was not enough room in mine to use the little hook mentioned.

Keep us posted with your results.
Dave

[20774]

An additional link to the insides of the speedos...

http://www.pbase.com/dwerbil/1978_r1007_odometer_repair