Speedo question

[officerbill]

Hi,
Anyone got a clue why the speedo would read about ten miles an hour slow at all speeds?
Thanks,
Bill

 

[almarconi]

Have you changed the size of your front wheel/tire?

 

[officerbill]

Standard eq. had it apart several years ago, cleaned and oiled what needed to be oil and reassembled. (I didn't go to far in the disassembly, just enough to get my clock oiler into the gears and give them a drop or two). The speedo was slow before I worked it over and it is still slow.
Bill

 

[almarconi]

I suppose it is possible that the speedometer is out of calibration. I used to own a 1988 suburban with a speedometer driven by a cable. I ended up getting a speeding ticket, took the speedo to a place that checks calibrations and found that it was reading slower than my actual speed. Once they told me how much it was off I could compensate.

I'm sure there are companies that can calibrate a motorcycle speedo but haven't got a clue what it would cost. My bike has a GPS on it and I usually use the GPS to track my speed. Depending on what the company would charge it may be cheaper to mount a GPS on your bike. Another option would be to install a used speedometer but there is no way of knowing how accurate that one would be.

 

[officerbill]

It could also be that I'm gaging my speed by the cagers around me. If my speedo is reading X in an X-10 zone and I'm keeping pace with all the little cars, could they all be speeding? I had a friendly chat with a Statie who told me I was doing 61 in a 40 zone, I would have sworn, not to him though, I was doing 70+. So, if I read the speedo at 45, I may be only going 35, but if I keep up with traffic they may be speeding. I need to ride with some one for a ways to see if I'm really off the mark, speedo wise.
Bill

 

[Nessism]

Inside the speedo, the cable turns a steel metal dome looking piece, and the needle mechanism must be magnetic since it indirectly picks up this movement and indicates the speed. The needle mechanism works against a spring, plus the needle movement is damped in some way. If the damping goes off, the spring gets weak, or if the magnetic attraction changes between the dome and the pickup, the speedo function will be off in some way.

Problem is that these units are not serviceable, nor can they be calibrated as near as I can tell. You can lube the gears that effects the odometer, but the speedometer function is independant of that and as near as I can tell, there is no way to service the damping action in the speedo needle mechanism itself.

 

[almarconi]

Problem is that these units are not serviceable, nor can they be calibrated as near as I can tell. You can lube the gears that effects the odometer, but the speedometer function is independant of that and as near as I can tell, there is no way to service the damping action in the speedo needle mechanism itself.

If the units are not serviceable then, a GPS would probably be your cheapest route for an accurate speed reading. If you like to do any exploring on your bike, the GPS is a great tool.

 

[bwringer]

At least borrow a GPS and get an idea of your real speed vs. your speedometer. Or, use a stopwatch and mile markers.

My GS850 speedometer is dead on for some reason. I have no idea how or why -- these devices are highly variable.

 

[Guest]

Take apart the speedo and make sure the spring returns the needle to 0. I make sure the needle sits on the peg on both sides. (Carefully lift it over the peg to the other side. If it moves away from the peg on the other side that is your problem.
Carefully pry the needle up from both sides protecting the guage face plate and reset it so it touches the peg on both sides.

 

[Steve]

It could also be that I'm gaging my speed by the cagers around me.

I have found that the only people you can trust less than "previous owners" would be the cagers around you.

One way to check your speed is to check your time through a measured mile. The mile markers on the freeway are usually close enough to get a good idea. If you don't have a stopwatch handy, at least get a watch with a second hand. If it is safe to do so, get your speedo to read exactly 60, check your time through a full mile. The formula is 3600/time=mph. For a few seconds on either side of 60, it's close to 1 to 1, so 55 seconds is 65 mph and 65 seconds is 55 mph.

Even better is to use a GPS, as you don't have to create a hazard by impeding traffic for a mile at a time, just compare the GPS reading with the speedo reading.

I seem to remember reading something several years ago that speedometers were supposed to read within 6% of actual speed, but could not read less than actual speed. Because production tolerances can go either side of design, manufacturers would set their target at -3%, then set the tolerance at +/- 3%. That is why speedos usually read faster than actual. Another reason is that the manufacturers would hope that weekend bragging, "I saw 125 mph yesterday" would entice a few more customers to their brand, even though the bike only actually did 115 mph.

It is rare that your actgual speed is more than what is shown on the speedo, but if the drive unit is not the correct one, it's possible. The 700 and 1100E models that came with a 16" front wheel had a different drive unit on the front wheel. It was geared for the smaller wheel. If you use one of them on a bike with a larger wheel, you would definitely be going faster than the speedo indicates.

.

 

[bwringer]

It's an age-old problem. Modern bikes always have speedos that read high. It's usually quite consistent within a certain model type. The DL1000 uses a pickup on the output shaft, so if you change gearing it gets even worse.

They could make an accurate speedometer, but they won't.

 

[blackhawk]

Nessism is exactly right on how the speedometers work. There is a magnet and spring involved. I have a 81 GS1100E and my speedometer reads about 15 mph high at 60mph (says that I am doing 75). I have been researching this and it looks like these can be calibrated. Only one speedometer shop said that they would do it for me and they wanted $75. A little high in my opinion. From what I have learned so far you can calibrate the speedometers in one of 2 ways. You can change the tension of the spring or the strength of the magnets. I am going to play around with the spring tension. I will report back if this works.

 

[chuck hahn]

i would take it to the shop..you stretch the srping the wrong way or snap it and you may never get it right again..let the pros do the job.that way if THEY ruin it you will have some backup to get it replaced. And what the heck 75 is nothing compared to all kinds of tickets and fines....just my opinion of course.

 

[TheCafeKid]

oR you just snag another speedo drive off ebay and hope its in better shape.. hell ive got three or four of em laying around here..

 

[Skateguy50]

GPS in view would work as an alternative

Here in Mass the speed is really only an issue at the dead of night, otherwise just try to not be the fastest or slowest on the road and you are ok. At times staying under the speed limit can be very dangerous on the highway, I find the left lane to be the safest and when someone is going way to fast coming up in my mirror I slide over and let them pass.

 

[tkent02]

or you could just put your own markings on the speedometer, like these:
http://www.thegsresources.com/_forum/showthread.php?t=130920&page=25&highlight=face+plates

 

[blackhawk]

I finally got around to try the calibration on my speedometer (81 GS1100E). I have not tried the bike out yet on the road, so I don't want to jinx myself, but I think that I have it calibrated. The spring in mine is a spiral one. The one end is attached to a brass collar that sits on the shaft. The second end is attached to a little sheet metal leg that is riveted to the speedometer body. This second end is sitting horizontal in the speedometer. The little sheet metal leg can be pushed in or out with a small screwdriver to easily adjust the tension on the spring. You only have to move that leg less than 1/64th of an inch to change the speedo reading. To ease Chuck's concerns, I don't see how you could break the spring unless you tried to move it some huge amount, like 1/2 an inch. If you move it too far, you jest bend the leg back the other way just a minor amount. I adjusted it 5 or 6 times to get it right.

Here is how I checked the calibration, since I knew that my odometer was measuring correctly. I borrowed a drill that turned pretty fast (2400 rpm) and used this to turn the speedo. I then ran the drill slowly to get the 1/10th mile part of the odometer to read where the top of the 0 was exactly lined up with the opening. I then ran the drill wide open for exactly 2 minutes. (I used 2 minutes instead of 1 minute, just to lessen the error.) After 2 minutes the odometer read just under 2.2 miles. So, 2.2 miles / 2 minutes = 1.1 miles per minute. So 1.1 miles per minute * 60 minutes per hour = 66 mph. My speedo should be reading 66 mph. My speedo was showing about 78 mph, so it was way off. I then kept adjusting that spring leg until I dialed it in to read 66 mph.

I actually had two other speedometers from 81 GS1100 bikes that a friend gave to me. (He used to buy junk bikes.) I tried the drill in these as a double check, just assuming they were correct. One read 66mph and the other read 65mph. With this double check, I felt pretty good. The road test will be the true one.

I took a picture of the inside of my speedo showing the spring that gets adjusted. I will try and post it soon.

 

[posplayr]

I actually had two other speedometers from 81 GS1100 bikes that a friend gave to me. (He used to buy junk bikes.) I tried the drill in these as a double check, just assuming they were correct. One read 66mph and the other read 65mph. With this double check, I felt pretty good. The road test will be the true one.

I took a picture of the inside of my speedo showing the spring that gets adjusted. I will try and post it soon.

Clever ; I use my drill to test spedos and tachs but never calibrate