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Offline RedbirdXR

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Speed Reading difference between Navigator and Speedometer?
« on: September 04, 2018, 03:38:28 PM »
I might be a bit picky, and this does not ruin my ride, but my Navigator 4 always shows 3-6 mph less than the speedometer.  I'm running the same size tires, same rims, OEM chain/sprocket. 

Does anyone have the same?  Has anyone confirmed if one is more accurate than the other?


Offline Norbs

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #1 on: September 04, 2018, 04:08:12 PM »
GPS is more accurate, I have never had a car or a bike that matches the GPS (gearing changes excluded). Cars tend to over read by 3mph at any speed. Bikes over read by 3mph aswell but this stretches even more the faster you go. 105mph on a bike is more like 100mph in real terms. If you were to go on the autobahn you'd see 150mph on the bike might only be 143-144mph on the GPS.

Online Speedy

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #2 on: September 04, 2018, 04:10:29 PM »
From my experience, nearly all motorcycle speedometers read/indicate faster than actual.  Trust the GPS.
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Offline aviator

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #3 on: September 04, 2018, 04:10:49 PM »
Yep, totally useless speedo. Its like BMW was giving you a false sense of how fast the bike is.  :008:
Hope they did not feck up with the emissions.
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Offline RedbirdXR

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #4 on: September 04, 2018, 04:17:09 PM »
Thanks all!

Offline Bree

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #5 on: September 04, 2018, 04:19:10 PM »
Yep got to add, that its fairly common knowledge that vehicle speedo's over read you actual speed. As others have said GPS is more accurate.   :305: :305:
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Offline PaulS1000XR

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #6 on: September 04, 2018, 04:36:42 PM »
Thats because the speedometers are calibrated assuming the tyres are nearly worn out rather than nearly new so the circumference of the wheel with a worn tyre is less ..... etc.   :305:
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Offline Bree

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #7 on: September 04, 2018, 04:39:08 PM »
 :005: :005: So are you saying Ive got to ride around on Knackered tyres to be accurate.  :001: :156:
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Offline PaulS1000XR

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #8 on: September 04, 2018, 04:51:31 PM »
*Originally Posted by Bree [+]
:005: :005: So are you saying Ive got to ride around on Knackered tyres to be accurate.  :001: :156:

Yes but its not compulsory  :305:
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Offline Martin

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Re: Speed Reading difference between Navigator and Speedometer?
« Reply #9 on: September 04, 2018, 05:24:42 PM »
Vehicle speedometers aren't calibrated, they are designed to over-read so that taking into account all normal errors and tolerances, you can never be travelling faster than indicated.

As your tyres wear down, the circumference gets smaller so the difference gets greater, i.e. the speedometer will over-read more as the tyres wear.

The integrated Garmin nav in my Mercedes is linked to the speedometer so the two always read the same, use a secondary GPS speedometer and as expected it reads lower.  Strangely enough I find that annoying and wish it was like the BMW so I could see the difference between road derived and GPS derived speeds.

On a similar note, I also find it annoying that BMW disable the fastest speed feature on the Nav VI  :164: :008: