A Different Speedometer Accuracy Question

[mzflorida]

I did not want to place this in "The Bar." Maybe it's the wrong place though.

It was @670cc who recently mentioned a speedometer correction device recently and it sparked my curiosity about a related performance element. I am back considering buying the BMW C400GT which is limited to 86MPH, I would imagine through the ECU, which contributed to my curiosity. I have a few questions.

• Am I correct in thinking that the data sent to the speedometer is the same data sent to the ECU (or whatever limits speed) for purposes of restricting speed?
• If so, and the data was inaccurately reported by the sensor to the ECU, would that translate into shifts on a DCT bike ocurring at points that were not aligned to the program for each ride mode (e.g. Tour S1, S2, S3)?
• Would a "speedo healer" correct the data sent to the ECU (or whatever limits speed) or only that data sent to speedometer display?
• If the answer is "no" to the above, is there a way to calibrate the speed data that informs the restriction function of the bike?

I'm clearly not a speed demon, evidenced by the fact I am thinking about another scooter. But, there are times that it would beneficial to accurately know how much potential you have left to plan certain maneuvers, such as passing, on a lower displacement bike. Plus, I appreciate precision and accuracy.

Could be a stupid question or thought process but thought I'd ask.
Mike

 

[TNHoosier]

I am not intimately familiar with the BMW C400GT. My experience with automotive ecu's tells me it would take an ecu reflash to achieve what you want. We did do work on the H-D V-rod ECU and it would require a reflash. Same for the jet-skis and snowmobiles we were working on at the time (late 1990's - early 2000's).

 

[670cc]

On the NC, and on my Goldwing and CRF250 (the latter two currently having speedo correctors installed) the correction device I use is connected immediately after the Vehicle Speed Sensor. The correction device receives a pulse train from the VSS, interprets it, then sends out a pulse train with a different repetition rate to wherever the motorcycle uses that signal. Thus, any function of the machine that relies on the VSS will receive a modified, corrected signal. Now, whether or how an ECU uses the VSS signal for any of it’s control, such as speed limiting or automatic transmission shifting, I don’t know. On my manual transmission Honda motorcycles, I think the speedometer is the only affected device.

On a semi-related side note that might be of interest, my Zero motorcycle has Eco, Sport, and Custom ride modes. The modes affect the maximum acceleration, throttle sensitivity, amount of regenerative braking, top vehicle speed, etc. Eco mode limits top speed to 70 mph, Sport mode is unlimited, and in the Custom mode configuration, the user can select the maximum vehicle speed. The behavior is refined yet interesting. When the bike reaches the programmed top speed, seen on the speedometer, the propulsion is just as smooth as ever, no hesitation or sputtering, but regardless of throttle position the bike simply won’t go any faster.

 

[mzflorida]

I am not intimately familiar with the BMW C400GT. My experience with automotive ecu's tells me it would take an ecu reflash to achieve what you want. We did do work on the H-D V-rod ECU and it would require a reflash. Same for the jet-skis and snowmobiles we were working on at the time (late 1990's - early 2000's).

Thanks. I guess what I want to get out of any mods would be a precise display of the speed while also ensuring that the right signal is being sent to the appropriate controllers on the bike. I'm thinking this might also impact cornering ABS if the actual speed is different from what the bike is measuring. I think the IMUs are informed by the speedometer as one measure (inferring really).

 

[mzflorida]

On the NC, and on my Goldwing and CRF250 (the latter two currently having speedo correctors installed) the correction device I use is connected immediately after the Vehicle Speed Sensor. The correction device receives a pulse train from the VSS, interprets it, then sends out a pulse train with a different repetition rate to wherever the motorcycle uses that signal. Thus, any function of the machine that relies on the VSS will receive a modified, corrected signal. Now, whether or how an ECU uses the VSS signal for any of it’s control, such as speed limiting or automatic transmission shifting, I don’t know. On my manual transmission Honda motorcycles, I think the speedometer is the only affected device.

On a semi-related side note that might be of interest, my Zero motorcycle has Eco, Sport, and Custom ride modes. The modes affect the maximum acceleration, throttle sensitivity, amount of regenerative braking, top vehicle speed, etc. Eco mode limits top speed to 70 mph, Sport mode is unlimited, and in the Custom mode configuration, the user can select the maximum vehicle speed. The behavior is refined yet interesting. When the bike reaches the programmed top speed, seen on the speedometer, the propulsion is just as smooth as ever, no hesitation or sputtering, but regardless of throttle position the bike simply won’t go any faster.

Thanks. I appreciate it. Where it resides in those two vehicle application certainly suggests that if the ECU receives the data after passing through the correcting device, while also controlling speed restriction, that the limit may more closely match the actual speed travelled.

 

[670cc]

Pertaining to the NC alone (not knowing anything about the BMW), I would think a good experiment would
be to simply temporarily disconnect the VSS, then ride the bike and see if all functions (except the speedometer) do or don’t work, including ABS, Engine, DCT, etc. But then, since the primary focus in this thread is the BMW, the NC’s behavior would be irrelevant.

 

[mzflorida]

Pertaining to the NC alone (not knowing anything about the BMW), I would think a good experiment would
be to simply temporarily disconnect the VSS, then ride the bike and see if all functions (except the speedometer) do or don’t work, including ABS, Engine, DCT, etc. But then, since the primary focus in this thread is the BMW, the NC’s behavior would be irrelevant.

That would be a good little test. I can try it on my Xmax first.

 

[lootzyan]

That would be a good little test. ...

This would be a test of the accuracy and veracity of the information in the Service Manual. According to it, disconnecting the VSS should have no effect on the bike's operation.

 

[670cc]

Another thought on this topic came to mind while I was riding. Honda, for example, surely has engineers that can design a perfectly accurate speedometer. However I believe when motorcycles are reading, say, 5% optimistic speeds, it was designed that way intentionally. Anecdotal evidence strongly suggests that NC speedometers intentionally vary in accuracy depending which country market they were built for.

So my point in all this is that a motorcycle or scooter could have a speedometer that intentionally reads 5% optimistic, while the ECU, if it has a reason to know vehicle speed, may be programmed to read the VSS signal correctly, and know the true vehicle speed. By correcting the VSS signal to make the speedometer correct, you might inadvertently be skewing the signal to the ECM, to make it compute an inaccurate speed, again if it even cares.

 

[gary]

Hi Mike,
i know this is not directly related, but may address your concerns on potential capacity for passing etc.
i recently saw a video showing top speed of the C400GT at 153 KPH. (about 94.86 MPH) i don't know the country of origin or the speedo accuracy,
but if the accuracy is close, it shows you may be able to get more than the restricted 84 MPH here with a remap ?
i'm guessing the CanAm didn't please your wife ? (or maybe you purchased that also)

 

[mzflorida]

Hi Mike,
i know this is not directly related, but may address your concerns on potential capacity for passing etc.
i recently saw a video showing top speed of the C400GT at 153 KPH. (about 94.86 MPH) i don't know the country of origin or the speedo accuracy,
but if the accuracy is close, it shows you may be able to get more than the restricted 84 MPH here with a remap ?
i'm guessing the CanAm didn't please your wife ? (or maybe you purchased that also)

Nope on the Can Am. She is not even riding her scooter and I'll probably be listing that this or next week. But like any other person, I am not going to encourage her to ride when she feels it is no longer right for her. Maybe a convertible?

Thanks for the heads up on the TS of the C400!

 

[HarveyM]

I always thought speed was generally limited by a rev limiter. That is once the red line is reached the spark is cut. Depending on the style it could be hard (no spark until revs reduced by a set amount) or soft (spark limited to say 2 out of 3 cycles).

 

[the Ferret]

Nope on the Can Am. She is not even riding her scooter and I'll probably be listing that this or next week. But like any other person, I am not going to encourage her to ride when she feels it is no longer right for her. Maybe a convertible?

Thanks for the heads up on the TS of the C400!

when my wife decided she could no longer ride with me as a pillion she decided to get her own ride, so last year she bought this

We have since taken it to multiple famous motorcycle roads lol

It's not a motorcycle, but it's a different kind of fun.

of course a few weeks ago, she also bought the PCX 150 scooter lol.

 

[mzflorida]

when my wife decided she could no longer ride with me as a pillion she decided to get her own ride, so last year she bought this

We have since taken it to multiple famous motorcycle roads lol

It's not a motorcycle, but it's a different kind of fun.

of course a few weeks ago, she also bought the PCX 150 scooter lol.

I like the Mustangs a lot and would not mind having one at all. Your wife has as good of taste in cars as she does in husbands! As an aside, unsure if others follow cars at all, but the VIN 001 of the new hybrid Corvette sold today here in Florida at Barett Jackson for $1.1 M! Charity purchase but still a lot of money.

 

[mzflorida]

Another thought on this topic came to mind while I was riding. Honda, for example, surely has engineers that can design a perfectly accurate speedometer. However I believe when motorcycles are reading, say, 5% optimistic speeds, it was designed that way intentionally. Anecdotal evidence strongly suggests that NC speedometers intentionally vary in accuracy depending which country market they were built for.

So my point in all this is that a motorcycle or scooter could have a speedometer that intentionally reads 5% optimistic, while the ECU, if it has a reason to know vehicle speed, may be programmed to read the VSS signal correctly, and know the true vehicle speed. By correcting the VSS signal to make the speedometer correct, you might inadvertently be skewing the signal to the ECM, to make it compute an inaccurate speed, again if it even cares.

That is very interesting. I get where you are coming from. But thinking about what @lootzyan posted, would it even matter or is there some other measure that is calculated specifically in DCT bikes to manage shifting? I apprecaite you adding more to consider and taking the time to think about it.

 

[mzflorida]

This would be a test of the accuracy and veracity of the information in the Service Manual. According to it, disconnecting the VSS should have no effect on the bike's operation.

View attachment 51721

Thanks. That complicates things for me a bit (regarding understanding). I would have thought for sure the shifts, at least, would have been tied to the VSS. IF it is not the VSS, do you know where it gets the data to perform the calculation to perform the shifts? Maybe RPMs and the selected driving mode? Guessing entirely.

 

[mzflorida]

I always thought speed was generally limited by a rev limiter. That is once the red line is reached the spark is cut. Depending on the style it could be hard (no spark until revs reduced by a set amount) or soft (spark limited to say 2 out of 3 cycles).

Very interesting and I have hit the rev limiter in similar circumstances...and accidentally. Thanks!

 

[670cc]

Thanks. That complicates things for me a bit (regarding understanding). I would have thought for sure the shifts, at least, would have been tied to the VSS. IF it is not the VSS, do you know where it gets the data to perform the calculation to perform the shifts? Maybe RPMs and the selected driving mode? Guessing entirely.

Your post jogged my memory. In the early days of NC700X, testers were stymied in trying to do dynamometer testing on the DCT. If the front wheel ABS sensor did not detect wheel rotation, the automatic transmission would never shift to second gear. Likewise, over the years, owners that had a rare broken or damaged front ABS sensor reported the bike would not upshift past first. So it appears that the DCT operation depends on the front wheel sensor. Also note that some manual transmission NC models have no ABS, but as far as I know, all DCT versions have ABS.

 

[dduelin]

Your post jogged my memory. In the early days of NC700X, testers were stymied in trying to do dynamometer testing on the DCT. If the front wheel ABS sensor did not detect wheel rotation, the automatic transmission would never shift to second gear. Likewise, over the years, owners that had a rare broken or damaged front ABS sensor reported the bike would not upshift past first. So it appears that the DCT operation depends on the front wheel sensor. Also note that some manual transmission NC models have no ABS, but as far as I know, all DCT versions have ABS.

I may be the only owner that cared about a dyno run and found out from Honda that the DCT limp mode can be turned off in order to shift through all the gears with the front wheel immobilized but the bike has to be plugged into a dealer's diagnostic computer to do so. The software is available only to authorized dealers. We ran 4 runs on my 2015 NC700XD using a Dynojet on 5/20/2016.

It is more complicated than just a functioning front wheel ABS sensor but I don't know much more than that. There are possibly at least 4 votes or data sources in the committee controls the shifting. The vehicle speed sensor (VSS) on the transmisson, the two transmission gear shaft rotational speed sensors (one may double duty as the VSS), and both wheel speed sensors. I believe the transmission control module can throw or detect temporary diagnostic codes from any one of the 4 that prevent normal DCT normal operation. Some DTC codes can reset by cycling the key off and back on. One time on a sandy unpaved road I excessively spun the rear whee up trying to get out of a hole. The ABS light illuminated and the DCT would not not shift out of first. I rode for a short distance limited to first gear but I was about 65 miles from home deep in a national forest. Fortunately the system reset after turning the ignition off then back on.

 

[lootzyan]

Thanks. That complicates things for me a bit (regarding understanding). I would have thought for sure the shifts, at least, would have been tied to the VSS. IF it is not the VSS, do you know where it gets the data to perform the calculation to perform the shifts? Maybe RPMs and the selected driving mode? Guessing entirely.

As I said, that would be a confirmation of the information from the Service Manual. It's not understandable for me either, but I haven't done such tests (disconnecting VSS) and I didn't have a need for it, and I won't have a chance to do it in the future.