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Discussion Starter · #1 ·
I was out riding the super slab (I-75) yesterday and had cruise control set, according to the speedometer I was cruising at 77 MPH yet the GPS indicated I was only doing 74 MPH. I have read and understand the slight variances between the 2 due to electronic issues. But I have never read or heard being 3 MPH off. Is it normal for a GTL to be out of calibration on its speed sensor?
 

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Yes. My 2015 is the same. And, I think it's a percentage off rather than a set MPH off. For example, my Harley was 2.6% off (haven't bothered to calculate it for the BMW), both in miles per hour and the odometer.

Sent from my Pixel 3a using Tapatalk
 

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Mr.Fix It
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With my aging eyesight I've never been able to accurately read the speedometer on my '12 GT; the speedometer dial leaves a lot to be desired. I refer to the NAV for speed.

Duane
 

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Every motorcycle I've ever owned, Japanese, US and Euro, have had speedos that read slightly higher than actual. Some more than others. Always figured it was intentional to avoid any possibility of the other way around. I'd prefer accurate, but it's not a big deal.
 

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Discussion Starter · #6 ·
With my aging eyesight I've never been able to accurately read the speedometer on my '12 GT; the speedometer dial leaves a lot to be desired. I refer to the NAV for speed.

Duane
I've got the same problem, so I have the display show the digital speed too, as I can't make out the fine details of the dial speedo either..
 

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There is always a positive speedo margin to allow the measurement difference due to tyre geometry as well as wear and pressure variations. Low readings may result in costly lawsuits.

Cheers,
 

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2021 K1600B Mars Red Metallic
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My 2021 1600B speedo also shows about 2mph slower when compared with the GPS but then again so have my previously owned motorcycles and most of the Cars, trucks and SUV that I've owned
 

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My 2021 1600B speedo also shows about 2mph slower when compared with the GPS but then again so have my previously owned motorcycles and most of the Cars, trucks and SUV that I've owned
EU Law prohibits vehicle manufacturers from ever showing slower (assuming you are running the spec'd tire size). There's even a rule/formulae.


5.3.The speed indicated shall not be less than the true speed of the vehicle. At the test speeds specified in paragraph 5.2.5 above, there shall be the following relationship between the speed displayed (V1) and the true speed (V2).

0 ≤ (V1 – V2) ≤ 0,1 V2 + 4 km/h
 

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K1600 GT SE 2011
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I work with cars, every car I have ever driven (with the exception of 1) and every bike I have ever ridden has had a speedo which reads faster than you are actually travelling, typically about 5-10%. Its only really since the advent of GPS that we notice the difference. Having said that, my Audi A2 speedo was out by the normal margin, but if I reset the average speed in the driver info display then its read out was spot on. So the car knew what speed it was doing but the speedo was calibrated to read high. The exception was a F355 Ferrari, its speedometer was bang on the money for some reason.
 

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K1600 GT SE 2011
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5.3.0 ≤ (V1 – V2) ≤ 0,1 V2 + 4 km/h
Doesn't that suggest the speedo should read the correct speed OR more (within 10% + 2.5mph). Not it must over-read...
 

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Doesn't that suggest the speedo should read the correct speed OR more (within 10% + 2.5mph). Not it must over-read...
Yep. They are not allowed to ever read slower. And you are correct that the vehicle knows the true speed. That's why the odometers are correct even though the speedometer reads high all the time.
 

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Preema
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ΔxΔp≥ħ/2 the greater the accuracy in knowing your speed, the less accurately you can know your position...

If you speedo was 100% accurate, your GPS would lead you into a lake!

So says Mr Heisenberg
 

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My Honda NC700X's speedo ranges from exactly actual road speed to reading ~1 - 2% higher than actual, depending upon which tire model I have on it, and the rear tire's state of wear.

The K1600's speedo reads a solid 5% higher than actual. The tires are pretty well worn out, so I'm curious to see how much closer it is when I replace them (and change tire make & model).

Concerning the EU rule about speedo accuracy: The US has such a rule, too, but it only applies to commercial vehicles. It's kinda amazing to me how lax and nearly pointless the rules are.
 

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Every motorcycle I've ever owned, Japanese, US and Euro, have had speedos that read slightly lower than actual. Some more than others. Always figured it was intentional to avoid any possibility of the other way around. I'd prefer accurate, but it's not a big deal.
Mine have ALWAYS been the opposite, speedo shows a few MPH faster than the GPS shows.
 

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Yep. They are not allowed to ever read slower. And you are correct that the vehicle knows the true speed. That's why the odometers are correct even though the speedometer reads high all the time.
The ODO's are not accurate either. After a long trip, my ODO and GPS distances are off by about 3% from each other in the same directions as the speedometer is off.
 
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