Commando Speedometer Error?

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northern750

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I've been enjoying my 72' Roadster for these past few weeks. Other than one exhaust flange loosening during a ride it has been trouble free and enjoyable.

I have a question about speedo error on these bikes: my machine has stock 19" wheels with Avon Roadrunners. The speedo needle is smooth, not bouncy. I get the distinct impression that the speedo is a bit optimistic, that it reads faster than my actual speed, based on the traffic around me on roads I often drive where drivers tend to stick close to posted speed limits.

Do these speedos have a reputation for reading a bit high or does my Commando give me the illusion of going slower than it actually is?

Thanks.

Derek.
 
Yeah, its a bit optimistic.

If you know what gearing you have, you can calculate road speed per 1000 RPM, but that would require a pretty accurate tach.

I would travel 10 miles on a highway at an indicated 60, and measure how long it takes you to click off 10 mile posts. If its exactly 10 minutes, then your speedo is accurate; if its 11 minutes, you're reading almost 10% high.

If your highway markers are metric, then you've got an additional conversion.
 
Based on my experience over the last few day, it appears my speedo is the opposite. Comparing the GPS speed (which I trust, having checked it in the car), mine shows a few mph slower than actual. What I recommend is you borrow a GPS from someone and check it for yourself. You will find GPS to be dead accurate.

Hope this helps.
 
My speedo reads about 70 mph when I am running at 60 mph based on an electronic bicycle speedo which I presume is pretty accurate.
 
Teach you a trick how I cheated. We have police speed signs that post your traveling speed.
I live on the east coast, Penna, USA.
It is radar and is spot on. If you have one of these in your area do a drive by say at 40mph.
Hold it steady at 40 and see what the illuminated speed response is.
My speedo is right on, but it only has 9082 orig. miles on the bike so speedo is still good.
Depending how old you speedo is it may have some wear factor as well.
Hope this helped 8)
Marshal
 
Here's another reference point: With stock tires and a 19 tooth sprocket you should be close to 16 mph per 1000 rpm. So 4000 rpm aught to be 64 mph. My speedo agrees very closely with my Garmin Zumo GPS.
 
Like Marshal i tried the roadside radar but all i ever got was " SLOW DOWN " :lol: One other way to check is by using your GPS . Select the speedometer screen and go for a ride . You will be able to check the accuracy by watching both the speedo and the odometer and calibrate as necessary.
 
my old triumph Bonneville 750 was off in the 1980's so I got my girlfriend in her mustang to ride next to me at 50 mph in her car.
We yelled back and forth till we were at 50. I was reading a little more.
Make sure she's a really good girlfriend before trying this :lol:
 
By the way, when you find out how far out it is, you can indeed adjust it yourself. If you take the speedo off and look underneath, you will see a small serrated screw, quite well protected, in the inspection hole. If you get in there with a small screwdriver or pointed instrument, anticlockwise adjustment will slow your speedo down and vice versa. My speedo went crazy and my Norton owning watchmaker friend stripped it, fixed it and returned it to me. He showed me this adjustment. It was running a little optimistically so I adjusted it and I now only need one more slight adjustment and she's spot on. Tachos are the same.
 
MarshalNorton said:
my old triumph Bonneville 750 was off in the 1980's so I got my girlfriend in her mustang to ride next to me at 50 mph in her car.
We yelled back and forth till we were at 50. I was reading a little more.
Make sure she's a really good girlfriend before trying this :lol:
Click to expand...

A girlfriend who owns a Mustang sounds really good to me :mrgreen:
 
My speedo is 5mph optimistic. On the same subject, what is the correct original speedo drive number for Commando...such as BG5330/xxx?

Thanks
 
Same problem in a `71 that I "un-mothballed" a couple of months ago after 12 years -- very smooth speedo operation, but reads about 12-13 mph FAST compared to a Garmin 60CSx GPS taped to the handlebars. I just put 1/4" white stick-on/stationery dots at each 10 mph point and annotated the correct reading w/ a Sharpie pen.

I'll send it off to Palo Alto Speedo when it gets too cold to ride this Winter
 
At least you folks aren't too far off. When we started testing the two prototypes, the speedos were so far out it was ridiculous. It turned out that someoine in design had specified an instrument that was calibrated for 1000 revolutions per mile and the speedo gearbox was putting out 1600 revs/mile. I don't think we got it corrected for the majority of the road test project.

It was relatively easy when you were running within the range of the instrument (50 mph read as 80), but once you got up beyond 120 indicated (actually 75 mph) you were completely dependent on reading the tcahometer and calculatiing what your speed was. Needless to say, running less than 75 when you're out on the open road and trying to break things didn't happen that often!
 
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