Road speed slow to update / Inaccurate

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ColinHorn
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Road speed slow to update / Inaccurate

Post by ColinHorn »

Hi all,

Recently bought an XT having had a 660 for years which I really liked. Am enjoying the new features but when riding, my displayed speed seems really slow to update and at certain speeds on cruise control where for instance, I know the bike reading 73mph is actually a true GPS 70mph the XT reads 68mph, it sometimes lifts to 70. Can't seem to find any way to improve the accuracy, all software is up to date.
electro_handyman
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Re: Road speed slow to update / Inaccurate

Post by electro_handyman »

First thing that comes to my mind is where are you riding. Any gps needs a clear open view of the sky to be able to 'see'/satellite signals. If I'm not mistaken any GPS unit needs to be able to see a minimum of 3 satellites to be able to triangulate location/speed data.
I know that when I was riding in the mountains earlier this year my XT would be a little slow with speed updates, but then so was my 550 in the past.
I have no idea, if you are riding out west, if the smoke haze from all the fires would have an affect on GPS signals.
ColinHorn
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Re: Road speed slow to update / Inaccurate

Post by ColinHorn »

Hi, thanks for your reply, I'm in the UK, Having had the 660 I have a direct comparison and at the moment, the XL can do a load more great things but the speed issue plus it's very slow to find where it is and update it's position after turning for instance.

I can't see anywhere to improve or calibrate the satellite signals.
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mzeist
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Re: Road speed slow to update / Inaccurate

Post by mzeist »

On the main screen there is a gps signal indicator in the upper left corner. press that for a few seconds and a screen appears with more GPS reception info. There is however no way to calibrate GPS signals.

What bike do you ride, the TFT from some bikes (ie Triumphs) seems to interfere with the XT GPS reception, which could explain your issue.

https://advrider.com/f/threads/triumphs ... t.1447709/
Groet, Marcel.
ST1300 - Etrex Vista, 60CS, Co300, SPIII, SP2610, Nuvi760, Zumo660, Or650, Nuvi3590, Zumo590/5, Zumo XT
ColinHorn
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Re: Road speed slow to update / Inaccurate

Post by ColinHorn »

Hi, I do ride a triumph, a 1200 explorer, interesting about the tft causing interference. Will get the silver foil out! :D
sussamb
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Re: Road speed slow to update / Inaccurate

Post by sussamb »

I had a similar problem with a cheap dashcam in my car. Upgrading to a more expensive one, dashcam not car, solved the problem
jfheath
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Re: Road speed slow to update / Inaccurate

Post by jfheath »

It is worth remembering that any domestic satnav speed display shows you the speed that you have been riding by calculating distance over time for the last few position fixes. It is always behind the actual speed for a few seconds.

As commented, the quality of the satellite fix plays a part if you are in built up areas; the presence of buildings, trees, passing artics can interfere too. Ford Heated windscreens play havoc.

And there is some 'smoothing' going which seems to have developed as Garmins satnavs have grown up. Eg if the signal drops, the satnav makes 'sensible' decisions. Try riding into a tunnel. The 550 used to complain immediately. One of the later ones (the 660) used to keep the last speed for a while before saying reception was lost. The 590 and XT keep showing the same speed until the signal returns. Speed up in the tunnel, the satnav speed stays the same, but when it eventually gets a signal, it has to catch up with your position further up the road than it thought. According to the satnav, you exit the tunnel like a cork. Well into 3 figures!

One other thing I have noticed - when stopped, after a short while it stops moving the icon around due to those small positional errors. It is ignoring the signal because there isnt much change. Goodness knows what else it ignores or rounds off.

One thing is for sure. You cannot rely on your satnav speed to be accurate just from a quick glance. If you are traveling at a constant speed and a good view of the sky and the display isn't changing, then it will be pretty much spot on.

What are you measuring your speedo against ? That might be wrong, although vehicle speedos will normally show less than actual speed.

Get a pillion with a stop watch. There are measured miles marked in various places in the Uk. Failing that, motorways have numbered marker posts every 100m.

Today, I discovered something really important. I found another way that doesn't work.

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