Bonneville America Forums Forums Technical Forums General Tech The Return of the Speedometer Error

Hey, all.

I was just reading some old threads on the speedometer error issue. I just acquired a Garmin 60CSX gps and mounted it to the handle bar...now I can see the error that everyone was talking about (with understanding that the gps would have a small error).

Has anyone figured out a way to calibrate the speedo?

Should I just go fast as hell and wait for a cop to tell me my speeds? (not a very efficient way to calibrate )

The mechanism inside is magnetically inducted, there is no adjustment. Well, you could move stuff around a little, but you could also make it a lot worse or even ruin the speedo. Just gotta live with it and figure out what your actual speeds are and remember them as you go an indicated 85 through town.
The local police here in Canandaigua will be glad to tell you on the ticket.
We also have a lot of those radar signs around that tell you how fast you are going, when ever they set them up I go back and forth to see how accurate mine is. Now I know.

Find a school zone on a sunday, they usually have those radar things mounted to a pole so you can check. How nice of them! I just figure 7 or 8% which is hard math to do, so I figure a couple MPH less than 10% over

One way to lessen the speedo error is to install a taller front tire. When my 33 Laser(110/80-18) wore out I couldn't find another one before I went on a trip, so I put on an ME880(110/90-18). The speedometer now reads only about 5% high instead of the usual 10%.

IF you knew exactly where everything is inside, you could probably drill a small, pluggable hole in the case and give it a tweak.
The common adjustment is to vary the tnsion on the return spring. On ones that have to be very accurate such as police ones, they also adjust the magnet airgap so that it is more liner.

On my bike, the speedometer seems to track accurately, but it is high by 10 MPH from about 30 on. I'm not sure what to do with that other than taking it all apart and rotating the dial. If I tried to set the spring tension, it would only be accurate at one point, and read under or over depending on whether I went faster or slower.

Is this common for these type of speedo's (on different makes)?

Went for a 250km ride with a buddy that had a new Heritage Softtail. Commented on him driving slow, taking it easy on the bike, he said he was doing 100kmh. Didn't tell him his speedo is out the same 10% as mine. In the US there is a standard as to the accuraccy of a speedo on a motorcycle (10%?), in Canada there is none according to the dealer.

Any Triumph I have ever ridden with has it. From my very first RAT ride in 02, the guys were talking about speedo error. Classics, sports, tourers, all of em.

I ride with a friend who owns a new 800cc kawasaki vulcan and his speedo's got the exact same error as ours. I'm thinking there's probably very few companies in the world who make motorcycle speedo mechanisms.

hmmm...sounds like a conspiracy. I vow to fight this problem with all my might and...ah, heck with it...I'm tired

Hate to encourage this but if these are pickup speedos then the speed correction box they sell for off-road trucks (big tire/rear end correction) should work. It justs counts the incoming pulses and creates another pulse signal at the corrected rate... http://www.ricksontruck.com/speedometer.html

these are purely mechanical speedos, pretty sure. I read somethingi n a car mag once that said even cars speedos are a wee bit off. They err on the side of caution.