1978 R100RS Speedometer

[stevenrankin]

What is the correct speedometer for the 1978 R100RS? I have a speedometer marked W1.112 in it now. Seem like I am going a lot slower than it it is indicating. Also the odometer is not working. Before I spend the cash to have the odometer fixed, I want to make sure it is the right speedometer. St.

 

[toooldtocare]

This is a photo of my now sold 78 R100RS Motorsport. The number on it is W-1.078, kind of hard to see from the photo. As you said, they are not correct. I removed the needle on mine and moved it back a bit, about 10 mph at 60 to correct it. Easy to do.

 

[beemerphile]

The number on the speedo needs to be correct for the final drive ratio that you are using. W=1.112 is for the 2.91:1 ratio (32:11) and the W=1.078 is for the 3.0:1 (33:11) rear. My 1977 R100RS came with 33:11 gearing and the 1.078 speedo. The ratio is stamped on the front nose of the final drive beside the small fill plug for the driveshaft lube.

 

[20774]

Lee -

I'm thinking you might have those final drive ratios and speedometer ratios mixed around. My '78 has the 33/11 rear end and 1.112 on the speedo. My speeds rear relatively accurately when doing timing runs...sorry, I don't have a GPS for absolute confirmation. That's also reflected here in Snowbum's page:

http://bmwmotorcycletech.info/ringgears.htm

As for the odometer not working, likely what is happening is that the wheels are not messing anymore. It's not too difficult to get to them, reengage them, and put a drop of glue on the end of the shaft. There's a very nice pictorial here:

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

 

[beemerphile]

Lee -

I'm thinking you might have those final drive ratios and speedometer ratios mixed around.[/url]

You are correct. I have a 1977 and a 1978 in boxes and mixed it up.

Sorry for the confusion. My 77 is 33:11 but I picked up the wrong speedo. Or vice versa. I'm not real sure as they are boxes of parts right now. The other thing that affects the speedo ratio that I didn't mention is whether it is an MPH or KPH speedo.

 

[stevenrankin]

Thanks for the replies

Well all, Thank you so much for the replies to my question. I have the correct speedometer for the final drive for my make and year according to Snowbum's chart. So I guess now, I can safely have it repaired.
Just seems like a heck of a lot of people were passing me when I was indicating 10 over the speed limit. I have a GPS on my phone I can check to see just how far off it is.
I have not had the bike on the road since I wrecked it in 2000. So memories of speed versus rpm and sensory memories are rusty.
It is a heck of a lot different ride on the 78 R100RS versus my 84 R80RT. St.

 

[stevenrankin]

Speedometer is just a bit off

Well, now I know why people were trying to run over me. When I indicate 60mph, I am only doing 50mph.
I have another speedometer to fit the bike with the same ratio number. So, I can try it out and see which of the two works or if either of them work.
If they don't work, one will go off for repair. St