DarkStar
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Re: Speedometer calibration ?

Sun Feb 26, 2012 6:54 pm

jkirkebo wrote:I have verified that the average speed is the correct one, by external GPS and radar speed displays along the road.

GPS is only as accurate as its own current accuracy and sample rate. Roadside radar speed displays usually display low due to using older RADAR technolgy and their positioning/aim on the road. Systems like LIDAR that law enforcement use are much more accurate and would probably be better to test your speedometer. Know any cops? :D
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garygid
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Re: Speedometer calibration ?

Tue Feb 28, 2012 11:40 pm

What is "GPS own current accuracy"?

+/- 50 feet out of 8000 miles?

100 feet out of 8000 x 5000 is one part in 400,000.

Sample rate in typical handheld GPS units is about 1/second.
In some cars perhaps 2 times per second.
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jkirkebo
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Re: Speedometer calibration ?

Wed Feb 29, 2012 2:32 am

DarkStar wrote:
jkirkebo wrote:I have verified that the average speed is the correct one, by external GPS and radar speed displays along the road.

GPS is only as accurate as its own current accuracy and sample rate. Roadside radar speed displays usually display low due to using older RADAR technolgy and their positioning/aim on the road. Systems like LIDAR that law enforcement use are much more accurate and would probably be better to test your speedometer. Know any cops? :D


Still, when external GPS, radar displays and the avg.speed indicator ALL agree on the speed (to better than +/- 1kph) and the speedometer displays 8% higher, I tend to believe the former three...

cwerdna
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Re: Speedometer calibration ?

Wed Feb 29, 2012 2:46 am

turbo2ltr wrote:It would seem very unusual for the speed to be high and the distance to be correct. They are usually derived from the same signal.

FWIW, you and others here might find this old article from 2002 interesting: http://www.caranddriver.com/features/sp ... er-scandal. There's also an easy to miss .pdf link from that article at http://www.caranddriver.com/var/ezflow_ ... 2a5a71.pdf.

There's some discussion of UNECE (!) regulations at http://priuschat.com/forums/gen-iii-201 ... ost1282138.

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garygid
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Re: Speedometer calibration ?

Wed Feb 29, 2012 10:16 am

The internal speed and distance values are as accurate as the car can manage (and circumstances like tire size and pressure permit).

It is only the DISPLAYED-to-the-driver speed that is "boosted".

So, the display-only speedometer "lie" does not affect the odometer or other internal speed or distance calculations.
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gasmiser1
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Re: Speedometer calibration ?

Wed Feb 29, 2012 10:22 am

I received a speeding ticket a few years back.

Speedo showed 55mph but I was actually going 68mph (freeway posted max was 55). It was that much out of wack.

I went to a Speedometer shop for calibration readings for proof to take to court to fight the ticket.

Judge said, "You aren't required to have a speedometer in the vehicle, you are just required to drive the speed limit."

I lost the case :evil:
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TonyWilliams
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Re: Speedometer calibration ?

Wed Feb 29, 2012 2:55 pm

jkirkebo wrote:My average speed and distance reads correct. If I accelerate to 80kph, set the cruise control and reset the avg. speed, it will show ~75kph after a while. I have to set the cruise control to 86kph for the average speed to read 80kph. .


I'm not sure if this is a good method. Why would it know the seemingly correct average after the reset at 80kph indicated on the display?

But, regardless, something doesn't add up. Have you tried the calibration settings in the service menu?

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garygid
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Re: Speedometer calibration ?

Wed Feb 29, 2012 7:53 pm

Where does one see the "Average Speed" displayed, please?
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2014 Tesla S, Model 3 in 2019
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derkraut
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Re: Speedometer calibration ?

Wed Feb 29, 2012 8:13 pm

Man! You guys crack me up with your "nit-picking". I mean, it must be frustrating to try to pick the fly-s$$T out of the pepper. Why don,tcha just drive and enjoy.... :roll: :roll: :roll: :roll: :roll:
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TonyWilliams
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Re: Speedometer calibration ?

Wed Feb 29, 2012 8:25 pm

The adjustment in the service pages, "Navigation", "Speed Calibration", is only +/- 2.5%.

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