Zumo User Forums

Les wrote: ↑Sat May 06, 2023 12:29 pm My Zumo 660, like many (not all) garmin units records highest speed, however it does not record when or where the speeds were achieved, so would be useless for any prosecution.

All of the Zumos that I know of from the 550, 660, 590, 595 and XT have recorded track logs, and you can turn them on and off. I have kept most of mine as a historical record of our longer tours. And they tell me where I was, what time and how fast I was going.
I do not know whether another copy is maintained in the system folder in a compacted format.

Speed is always calculated from positional fixes, and all sorts of stuff can affect the accuracy of the fix - trees, mountains, passing HGVs ...
If the position is subject to (say + or - 10m either way, then that is a difference of 20m for two consecutive readings for your actual position). 60kph is nearly 17m per second. So in just one second with, the satnav may have you covering anywhere between 3m or 37m in that 1 second- ie between 10.8km per hour or 133km per hour. (6mph to 83mph ish)

But - over a time period of say one minute, the positional error may still be as high as (say) plus or minus 10 metres. In a minute at 60kph you will travel one kiliometer. With the error, the satnav will calculate this (in the extremes) as either 980m or 1020m

980m in one minute is 58.8 km per hour
1020m in one minute is 61.2 kph.

I've used kilometres because the maths is easier to understand. But you can see that although a fix at a particular point in time is impossible to achieve, a distance / time calculation over a minute is much more convincing - even with the exaggerated + or minus 10m error that I described.

Especially if the speed limit was 40kph.

10m is a big positional error for a satnav, by the way - you may see it just turning it on, but once it has got a fix on a few satellites it drops pretty rapidly to 3-4 metres. I'm inside at the moment and mine is showing an accuracy of 3metres. It took about 20 seconds to get enough satellites to reach that level of accuracy.

Becasue of all of the above, the satnav never shows you the speed that you are currently travelling. Its shows you the speed that you have been travelling in the last few seconds. If this is in the last 5 seconds, it works out the distance travelled from where you are now to the point you were at 5 seconds ago, and displays that as a speed. It seems to update it every second and it settles to your current steady speed after around 5 seconds.

If you are travelling at a constant speed with no mountains around, a clear view of the sky, no buildings or passing trucks and the satnav speed is staying pretty steady and is showing a speed that is the same value different from you speedo - then it is a good indication of you true speed.

The speedometer will never show you travelling faster than your true speed - so if it shows you doing 60mph, you will definitley be doing 60mph or less. Never more.

You cannot rely on the satnav for that. It may show 60mph and you could be doing a good few mph faster than that. Not often, but it is possible.

And just for amusement. This is the speed profile drawn fromthe gpx file of my track log.
Where those spikes come from, I do not know. But they are completely spurious. Yet they have been recorded in the log. I have watched the video - which shows the speed from another GPS receiver and the lat/long coordinates. There was no sudden change in speed. Maybe it was a fault in the satnav or the GPS receiver, or maybe the fact that I was riding through Snowdonia and the view of the satellites was limited. I don't know. My current Zumo doesn't do this.

The red line is closer to the actual plot speed and I've just drawn that freehand. But if you take a look at the actual speed recordings in your GPS file, they can be quite alarming. Probably not as extreme as my 2nd XT satnav, but they certainly need smoothing out.

If the cops could be botherd and knew there way around the Zumo they would find that. But who is to say you did that on the highway, could have been on a track or private road

They could also read this from your tracks stored on the Zumo. I would not worry too much. And no, I don't think you can turn it off

Not to make things even more complicated, i have been trying hard not to make a remark. (I failed)

But lets consider this very hypothetical example:

You get ticketed, and you're sure you were not driving to fast. Could you use the tracklog to prove this?
I doubt the police would accept the tracklog as proof. So how can they use the tracklog to prove you were speeding?

The tracklog, as is the max. speed recorded, simply does not qualify as proof, in my view.

I'm not worried about it - I'm just providing information.

And each point in the track log is accompanied by the lattitiude and longitude, elevation, date, time, speed, course (bearing)

Eg - taken from my track log, with the location altered to a different location in the same format.
<trkpt lat="53.97474" lon="-2.02729">
<ele>106.36</ele>
<time>2023-04-15T08:55:17+01:00</time>
<extensions>
<gpxtpx:TrackPointExtension>
<gpxtpx:speed>12.35</gpxtpx:speed>
<gpxtpx:course>196.24</gpxtpx:course>
</gpxtpx:TrackPointExtension>
</extensions>
</trkpt>

And one of these is recorded every second or so - it depends on how fast you are moving. There's no point in recording a point if it is very close to the last point.

This track log is recorded in GPX/CurrentTrackLog.gpx on the Zumo XT, with a copy in the system folder DriveLog - with a slightly different name. Older logs are stored in the Archive Folder. On the 590 and 595 the filenames are the same, although I think Drivelog is relatively new - at least, I never noticed it before. On the 660 the current track log was called something else, I do not remember waht it was.

You can stop them from being recorded on most Zumos. On the XT it is in Settings->Device->Travel History. Untick it. The other Zumos had the option in a similar location.

But - as I said before, whether there is another copy that cannot be turned off, I do not know. If you know better, then I would be pleased to learn about it.

@Peobody

I have heard mention of someone that used the track log to suggest that he was not speeding, and that was enough to raise doubts. But I cannot quote it, so unless I can find it again its just anecdotal. But the max speed - no. It is prone to capturing every single rogue value that was greate than the last one. Never the other way.

I have heard - again anecdotal - that police can monitor the speed of approaching vehicles from the info communicated constantly with cellphone towers.

jfheath wrote: ↑Tue May 09, 2023 6:55 pm You can stop them from being recorded on most Zumos. On the XT it is in Settings->Device->Travel History. Untick it. The other Zumos had the option in a similar location.

To be clear, this does not disable the max speed record; it just disables logging.

Is Norway police so anal about speeding??
I see all European bikers are covering their speedo on YouTube. Looks like the police has no other things to do just to watch the YouTube for speeders lol .

In some country's here in Europe you can be filed when a video in the course of an investigation is showing that you are way off the allowed speed, but - this only counts for a vehicles speedometer, because they must(!) be within a certain range of the exact speed (i think a difference in between 5 to 10% is allowed)...

Rofor wrote: ↑Wed May 10, 2023 8:25 am In some country's here in Europe you can be filed when a video in the course of an investigation is showing that you are way off the allowed speed, but - this only counts for a vehicles speedometer, because they must(!) be within a certain range of the exact speed (i think a difference in between 5 to 10% is allowed)...

Uk and europe, the speedo must never show less than the actual speed in any conditions. They may show more than actual speed - I believe it is up to 10% plus about 2mph for a motorcycle. So at a true 70, it may (just) legally show 79mph. But not 69.9. The majority will show somewhere in the middle of that range - 75. Which is possibly why many people believe that all speedos read 10% too high. Mostly that would be about right, but yours may be one of the few that read at the extremes of that range.

The manufacturing figure was 10%+5mph for a motorcycle (6.25mph for a car). It has changed since I last looked it up

When I travel by Air I take my current GPS with me and have it record the top speed.

I did in the past get pulled over by an officer for speeding. He wanted to look at my top speed (this was with my Zumo 660.) I said sure but it won't help him. When I showed it to him he broke out laughing because it was at 900+ kph. I said my bike was fast but not that fast.

He didn't give me a ticket.

In Ontario, Canada my understanding is that GPS info can't be submitted in court. However if an officer sees a (Realistic) high speed he may figure we are in the habit of going fast and might not cut you any slack.

..Tom

They have no right to look at your GPS. Still by refusing to let him look you have a better chance not to get a brake.

On a side note, I couldn't get a reading in the air for some reason...