Speedo calibration - Ducati Monster S4

[Duc]

Anyone know if it is possible to calibrate the speedo on a 2002 S4 Monster?

Where? How?


GPS informed me my speedo reads approx 10 kph low at critical speeds:

eg speedo 100kph = GPS 90 kph

speedo 120 = GPS 109 kph

I want reasonable accuracy in this speed range so I do not need to do mental math as I ride.

Upside: I can travel a little faster than I thought I could previously.

[vifferman]

Well, if it's electronic, you can fit a speedo corrector to it. Jaycar sell a simple kit that's not too hard to put together. (I've got one fitted to the VFR to allow for lowered gearing).
The only problem is this: most speedos are deliberately optomistic (read high), whereas the odometers are fairly accurate. I believe this is done for legal reasons, so that if people are caught speeding it's not because their speedo is lying, so they (i.e., Mrkns) can't sue the manufacturer. But (however) the odometer has to be pretty accurate so the vehicle's not under-recording the mileage and misrepresenting that.

SO, if you DO adjust your speedo (however you do it), be aware that your odometer may be out (i.e., over-reading) by more than 10%.

[Duc]

Thanx - I'll take a look.

Thats the weird thing. The speedo is out 10% and the odo is accurate. Id rather have the speedo correct.

Ducs use bolts on the rear wheel hub, read by a sensor so gearing changes etc do not make a difference .

[NighthawkNZ:Me]

Thats the weird thing. The speedo is out 10% and the odo is accurate. Id rather have the speedo correct.

I just use a mix of GPS speed and the speedo which is out by 7 odd kph

[NinjaNanna]

Why are you assuming the GPS is right and the bike is wrong?

Have you cross referenced it in your car?

Personally I would put little faith in a GPS reading (it may be old information) but I thought standard GPS units were only good for an accuracy of +-3m

If this is true I certainly wouldn't be relying on it for an accurate speed calculation.

Found this on wikipedia

[edit] Accuracy and error sources
The position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal. The position accuracy is primarily dependent on the satellite position and signal delay.

To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version. By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about 1% of a bit time, or approximately 10 nanoseconds for the C/A code. Since GPS signals propagate at the speed of light, this represents an error of about 3 meters. This is the minimum error possible using only the GPS C/A signal.

Position accuracy can be improved by using the higher-chiprate P(Y) signal. Assuming the same 1% bit time accuracy, the high frequency P(Y) signal results in an accuracy of about 30 centimeters.

Electronics errors are one of several accuracy-degrading effects outlined in the table below. When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft). These effects also reduce the more precise P(Y) code's accuracy.

Sources of User Equivalent Range Errors (UERE) Source Effect
Ionospheric effects ± 5 meter
Ephemeris errors ± 2.5 meter
Satellite clock errors ± 2 meter
Multipath distortion ± 1 meter
Tropospheric effects ± 0.5 meter
Numerical errors ± 1 meter

[duckonin]

Darn some up to 10% incorrect and I thought I was going fastthats why I didn't get the ticket my wife said I was going to get speeding past our local ticket giver... ha ha Actually I used that as my defence after receiving a ticket in the mail for 61k's in a 50 speedo calibaration was out ha ha didn't work still had to pay but I tried, nice picture of the bike and wifes pink jacket though so we got something for our money...

[Duc]

GPS Accuracy - your info mainly refers to positioning and not speed. Known issue that I have observed many times in boats.

I tested my GPS unit in three cars and when I did the test on my Ducati ,I had a companion on another bike . We had a pre arranged signal where I could indicate the GPS speed reading to him and he could check his speedo. My Ducati was the only vehicle that displayed the wide error/difference. I trust the GPS unit.

This type of speedo error is widely reported in Ducatis and many other MBs.