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 Speedo / ODO accuracy and relationship

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motomoto

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PostSubject: Speedo / ODO accuracy and relationship   Thu Oct 22, 2015 4:31 pm

I have a dumb question here.   I just don't understand how adjusting the speedo to be accurate doesn't also make the ODO accurate.

(Using American units here)

If

speed = (miles/hour)

and our speedo is correctly expressing our speed.  Then as long as our speedo has an accurate clock

distance = (speed) * (time)

our distance should be accurate as well.  Why do most people experience that their ODO is off after correcting their speedo?
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Jens Eskildsen




PostSubject: Re: Speedo / ODO accuracy and relationship   Thu Oct 22, 2015 5:20 pm

The odo is correct form the factory, but the speedo is like 8% of. So anyway you ajdust it, you'll have that difference.

You could ge the odo 4% low and the speedo 4% high, but then neither will be really accurate.
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motomoto

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PostSubject: Re: Speedo / ODO accuracy and relationship   Thu Oct 22, 2015 8:33 pm

Does anyone know why the odo is off from the speedo?
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Jens Eskildsen




PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 3:19 am

Speedo is too high, so people can say they can reach arund 100mph on a 250 GAHHHH

It seams like most bikes theese days are way optimistic. My old 1982 xt550 with cable-driven speedo is way more accurate.
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DutchTerror




PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 7:14 am

motomoto wrote:
Does anyone know why the odo is off from the speedo?

I believe there was a mandate/law/rule, whatever you want to call it that indicated speed had to be greater than actual speed. Some manufacturers and models hold this to a tighter tolerance (+1-2mph), whereas some are much further off. My old Yamaha V-Star 1100 was only 1-2mph high at 60mph. My Super Tenere is 5mph high at 60mph. I my WRR was like 8mph high at 60mph. I think part of the excessive amount may also be due to the potential for a larger lug tire (like a knobby) that indicates one speed when new and another speed when extremely worn out.
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Mozart 2




PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 9:23 am

No one has addressed Motomoto's original point/question (a question I too have often pondered). It's not an issue of if or why the speedometer is off .
The computer calculates speed by measuring distance (via the transmission output) and then compares distance traveled to the elapsed time via an internal clock (as per Motomoto's original equation). Unless the clock is also off, the error has to be in the distance measurement - presumably the same distance measurement used for the odometer.
I wonder if the speed healer correction circuit is correcting the speed number AFTER the speed calculation. If this is the case, then the speed healer shouldn't have any effect on the odometer reading. Does anyone know if this is the case? Or does the speed healer circuit change both speedometer and odometer readings...?
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DPete

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PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 9:40 am

I thought mine was off, 8% @ 60=4.8 mph slow. No wonder I never get a ticket Very happy
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motomoto

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PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 11:01 am

Mozart 2 wrote:
No one has addressed Motomoto's original point/question (a question I too have often pondered). It's not an issue of if or why the speedometer is off .
The computer calculates speed by measuring distance (via the transmission output) and then compares distance traveled to the elapsed time via an internal clock (as per Motomoto's original equation). Unless the clock is also off, the error has to be in the distance measurement - presumably the same distance measurement used for the odometer.
I wonder if the speed healer correction circuit is correcting the speed number AFTER the speed calculation. If this is the case, then the speed healer shouldn't have any effect on the odometer reading. Does anyone know if this is the case? Or does the speed healer circuit change both speedometer and odometer readings...?

Thanks for re-iterating the question.  I always find it useful to see questions posed from different people's perspective.

If there is truly some mandate for motorcycle speedometers to read high I could see how the manufacture would purposefully induce a bias into the speed calculation but make the odometer accurate for maintenance purposes.  This almost borders on conspiracy theory here but so far it's the only thing that makes sense to me.  

I plan on putting on a 48T rear sprocket soon and I'll probably pick up a speedo healer/DRD.  Maybe I'll spend a little time looking at the installation or wiring diagrams to see what I can discern.  I design electronics and software for a living but don't have much experience with motorcycle maintenance and modification.
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DutchTerror




PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 11:21 am

Per the United Nations Economic Commission for Europe:

http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r039r1e.pdf

See section 5.3.

And the Wikipedia version here:
https://en.wikipedia.org/wiki/Speedometer#cite_note-6
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Jens Eskildsen




PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 11:51 am

Mozart 2 wrote:
Or does the speed healer circuit change both speedometer and odometer readings...?


Jens Eskildsen wrote:
The odo is correct form the factory, but the speedo is like 8% of. So anyway you ajdust it, you'll have that difference.

You could ge the odo 4% low and the speedo 4% high, but then neither will be really accurate.

I'll try to say it another way. It changes both, again, thats why you can only have one of them to be 100%, the other will differ the same amount as the differences between odo and speedo on the stock bike. Currently theres no way around it. And its really not that big of a deal.

You get used to it.
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greenboy

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PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 2:45 pm

Just to underline all this, from SpeedoDRD FAQ --

"Odometer vs Speedometer Correction Explained...
SpeedoDRD does allow for Speedometer and/or Odometer correction, although sometimes getting them both 100% correct continuously is not possible, this is because some vehicles have an odometer error rate which is not equal to the speedometer error rate, since your ECU or Gauge Cluster uses the same signal to determine both the odometer reading and the speed reading, this type of problem lies within the ECU or Gauge Cluster itself. If you find yourself in this situation, you will be able to get your speed 100% and the odometer very close. Or you can choose to get the odometer 100% and the speed very close, or you could even choose a happy medium between the two, and get them both equally close, its up to you, and it depends on how far apart the two error rates are from each other."

Stock WR250R gearing and tire error is said to be 7.7%
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wwguy

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PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 3:55 pm

My professional experience includes 20+ years working with industrial instrumentation and control systems.  While I don't profess to know exactly how the WRR odo/speedo circuit operates, the operation explained here and elsewhere aligns with my previous experience, as well as the WRR wiring diagrams in the service manual.  That's fancy way of saying I'm about to make an educated guess.

There's a single sensor, probably either a magnetic or inductive pickup, that feeds a series of pulses from the transmission output shaft to the ECU.  The ECU is a small computer which does some math with the sensor input to convert it to MPH/KMPH (speed) and miles/kilometers (odometer) and then passes that along to the dash display.  The ECU math is factory set and not user-programmable.  It also includes roughly 7.7% error in the speedometer calculation as discussed previously and verified over and over by WRR riders.

SpeedoDRD and similar "calibration" devices are user-programmable signal conditioners that are added inline between the transmission speed sensor and the ECU.  They can be programmed to increase or decrease the signal pulse rate sent to the ECU.  Programming these devices is a matter of setting the ratio of actual pulses detected to those sent to the ECU.

The 7.7% speedometer factory error rate in the ECU never goes away.  It just appears that way because the speedometer "calibration" devices increase or decrease the number of pulses sent to the ECU until the speedometer indicates the desired actual speed.  So the speedometer calibrator is actually intentionally introducing error in the signal source to compensate for the factory error in the ECU speed calculation.  The side effect of this is that the intentionally induced signal error is also passed along to the odometer calculation in the ECU.  So the odometer that was previously accurate is now in error equal to whatever % pulse change  you programmed into your speedo calibrator to correct the speed calculation.

With only one pulse source (the speed sensor) and only one pulse receiver (the ECU) there's no way to make two modifications to the signal.  So you have to choose.
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motomoto

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PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 6:13 pm

wwguy wrote:
My professional experience includes 20+ years working with industrial instrumentation and control systems.  While I don't profess to know exactly how the WRR odo/speedo circuit operates, the operation explained here and elsewhere aligns with my previous experience, as well as the WRR wiring diagrams in the service manual.  That's fancy way of saying I'm about to make an educated guess.

I have a similar background.  I'm an electrical engineer and I design PCBs and write C/C++ code for embedded systems.  I've built some devices that are not entirely dissimilar to the speedo re-calibrators myself.  I fully agree with everything that you said and I think that you've stated it very well.  Thank you!

I guess my original question was not so much "how does all this work" but more of a big "why is it like this"?

DutchTerror wrote:

Per the United Nations Economic Commission for Europe:

http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r039r1e.pdf

See section 5.3.

And the Wikipedia version here:
https://en.wikipedia.org/wiki/Speedometer#cite_note-6

This is actually very interesting to me.  Looking at section 5.3 of the pdf gives an equation for the relationship between indicated speed and true speed.  Likewise, the wikipedia article makes a couple of statements about error

wikipedia wrote:


  • The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
  • The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.


So, in the end, I guess it's true that the manufactures pump up the indicated speed deliberately!  Thanks for all of the input guys!
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wwguy

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PostSubject: Re: Speedo / ODO accuracy and relationship   Fri Oct 23, 2015 9:18 pm

Sorry for any confusion about the intent of my post.  I was attempting to answer this question:

motomoto wrote:
Does anyone know why the odo is off from the speedo?

... and to clear up what I believe are misconceptions stated in this post:

Mozart 2 wrote:
No one has addressed Motomoto's original point/question (a question I too have often pondered). It's not an issue of if or why the speedometer is off .
The computer calculates speed by measuring distance (via the transmission output) and then compares distance traveled to the elapsed time via an internal clock (as per Motomoto's original equation). Unless the clock is also off, the error has to be in the distance measurement - presumably the same distance measurement used for the odometer.
I wonder if the speed healer correction circuit is correcting the speed number AFTER the speed calculation. If this is the case, then the speed healer shouldn't have any effect on the odometer reading. Does anyone know if this is the case? Or does the speed healer circuit change both speedometer and odometer readings...?
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motomoto

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PostSubject: Re: Speedo / ODO accuracy and relationship   Sat Oct 24, 2015 2:57 pm

Fair enough.  Honestly, I think you answered the question as asked.  Guess I didn't really know what I was after until we explored the topic somewhat. dunno
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