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Discussion Starter #1
Hey guys I turned on my digital speedo and noticed that the digital read out didn't match the analog readout. The analog readout appears to be about 2 mph faster than what my digital speedo reads. Just wondering if this is normal or I should get it checked out at the dealer.
 

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All speedo's are off, on every brand car. The speed on my Tom Tom Navigation, is also different from the speedo, compare to the 500. Don't waste a trip to the dealership. I really think you car is pretty normal.
 

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my analog reads a tad faster than the digital readout, and my clock loses time.
now we know why italy never was a technological threat to the swiss, germans, or japanese lol
 

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All speedo's are off, on every brand car. The speed on my Tom Tom Navigation, is also different from the speedo, compare to the 500. Don't waste a trip to the dealership. I really think you car is pretty normal.
Not trying to get technical here but when you refer to your Tom Tom Nav speed are you referring to to speed estimate? Or does the Tom Tom unit pull data from the car? Because unless it's pulling data from the car the speed is going to be based on the delta time between samples of location data which leaves a relatively high percentage of error.

If this is a common thing does anyone know which readout is more accurate?
 

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GPS speed is more accurate that you can read the speedo.

Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on.
We use GPS data loggers on race cars these days, and they are VERY accurate.
 

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Hey guys I turned on my digital speedo and noticed that the digital read out didn't match the analog readout. The analog readout appears to be about 2 mph faster than what my digital speedo reads. Just wondering if this is normal or I should get it checked out at the dealer.
I know what you mean, the needle points to a different speed that the digits rendered.. mine too, and my new fixed clock is now 2mins fast every couple/3 weeks vs 2 mins slow every 2 weeks... woo wee!
 

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mine is the same way. the digital is closer to the speed signs around town and thats what i judge my speed off of. so i stick with the digital readout. its not perfect but its close enough for me.
 

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Discussion Starter #8
GPS speed is more accurate that you can read the speedo.



We use GPS data loggers on race cars these days, and they are VERY accurate.
The precision of the data will depend on the chipset, antenna, and power of the device. I'm sure the loggers on race cars extremely sophisticated, but the precision of a vanilla TomTom unit is questionable. TomTom won't provide the chipset they use but they probably use a low end SiRF or Infineon chipset in their unit.
 

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Not trying to get technical here but when you refer to your Tom Tom Nav speed are you referring to to speed estimate? Or does the Tom Tom unit pull data from the car? Because unless it's pulling data from the car the speed is going to be based on the delta time between samples of location data which leaves a relatively high percentage of error.

If this is a common thing does anyone know which readout is more accurate?
I would assume my GPS to be the most accurate of the 3 speedometer reading. I've been side by side more then once, with a Honda Civic, on the highway with the large digital speedometer read out on they dash board. A different speed is showing on their car too. Speedo are accurate up to maybe 5-6 mpgs, I'd would guess.

Again I don't think, anything wrong, with the OP's car.:)
 

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Discussion Starter #11
All analog gauges become uncalibrated over time, it's the nature of a physical device to change over time.

I understand that the accuracy of instantaneous speed is different between vehicles. However, why is it that if the analog and digital speedo get their speed data from same source ( transducer to canbus, correct? ) do they give significantly different readings?

So far it seems this is normal for the 500's to have this bug. Italian cars are known for having poor electrical systems so I'm not surprised I suppose. I wonder if Jonathon can ask an engineer for me?
 

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Is the needle really analog????? Just looks analog. Maybe the needle doesn't respond as fast, as a read out. Both readings come from the same digital source. Italian cars were know for poor electric systems maybe back in the 1970's. Speedometers use to be hooked up to old cables, down to the tranny's. the cables use to wear out. Not today cars.


Your car is brand new why would it be worn out already???? Many???????
 

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I thought about the response time playing a role and came to the conclusion that it isn't so. Because if I maintain 40mph on the digital readout the analog output is always the same 43-42mph.

A physical output is always analog. The needle is an analog output but the canbus is digital. So the digital electronic signal has to be converted to an analog electric signal. Either the digital to analog has a bug, or the gauge itself is faulty.
 

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my analog reads a tad faster than the digital readout, and my clock loses time.
now we know why italy never was a technological threat to the swiss, germans, or japanese lol
Super LOL!
 

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The precision of the data will depend on the chipset, antenna, and power of the device. I'm sure the loggers on race cars extremely sophisticated, but the precision of a vanilla TomTom unit is questionable. TomTom won't provide the chipset they use but they probably use a low end SiRF or Infineon chipset in their unit.
Some big assumptions. Not all race dataloggers are high end expensive units. Many are in the price range of basic nav GPS units.

And that ignores the quote I supplied about the accuracy of the Garmin GPS units. And I suspect the Tom Tom, even in worst case, is accurate to withint 1 MPH.

And do you know how an analog guage works? If so, tehn you can figure out why the analog needle may read differently than the digital readout, that takes direct digital speed info from the transducer.

And they are both still more accurate that BMW speedos. BMW spec is to read not less than the actual speed and not more than 2.4 MPH + 10% of the actual speed. So at 60 MPH, BMW speedo could be reading 68.4 MPH and be considered within the spec.
 

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All speedo's are off, on every brand car. The speed on my Tom Tom Navigation, is also different from the speedo, compare to the 500. Don't waste a trip to the dealership. I really think you car is pretty normal.
I agree with Smark.. within specs seems to be within 0-3 miles per hour on the readout. Comparable also to the navigation..
 

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I went up to car wash, this morning. I have a sport, with a dark dial. I don't even how you can tell if both of them were accurate not. The needle on the speedo, is really wide. The incriments on the dial are really crude. I'll stick to the digital out. Worry about nothing!!!!!!!!!
 
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