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Old 12th March 2019, 08:24   #1
LittleMan
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Default Mileage reading

Today I have observed something warring: is it possible for my new second hand acquired 75 to read lower mileage?
I'm based in NZ, and the dashboard is in km. The speed is about right, 90km/h being actually 86-87km/h on GPS, as any other car.
Car is facelift, 2005 made.
So, I leave from work and see that the trip computer shows only 25.4km.
Get home, and is 50.9km. That's 25.5km. But my commute is at least 28km (my other cars always recorded 28.3-28.4km on same road). I've checked again with google maps, and is indeed 28km.
What should I check? Or the transformation from miles to km does not work well?

Thank you!
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Old 12th March 2019, 08:29   #2
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Check the tyre sizes on you new car. If the tyres are larger than recomended it would record a shorter distance than a smaller tyre. Less revolutions! Just an idea.

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Old 12th March 2019, 09:40   #3
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Of course, checked those first: 215/55R16 everywhere (although all are different models...no comment).
But the idea is the GPS speed to speedo is fine. Why is the recorded mileage lower by ~10%?
If that's always been the case since new, I wonder if the car has actually at least another 10k km...
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Old 12th March 2019, 14:39   #4
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Quote:
Originally Posted by LittleMan View Post
Of course, checked those first: 215/55R16 everywhere (although all are different models...no comment).
But the idea is the GPS speed to speedo is fine. Why is the recorded mileage lower by ~10%?
If that's always been the case since new, I wonder if the car has actually at least another 10k km...
Some time ago there was talk of legal action against car manufacturers based on "optimistic" speedometers (5%-15%). It was thought that the cars were racking up mileage to the maximum listed in the warranty 5%-15% quicker than reality and saving manufacturers money by the warranties ending early. It turned out that while the speedometers had that buffer to prevent unintended speeding, the odometers were accurate. How? I don't know. Measured against GPS? I don't know. Just thinking out loud.

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Old 12th March 2019, 16:01   #5
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Quote:
Originally Posted by LittleMan View Post
- - - the trip computer shows only 25.4km.
!

It might be interesting to check if the Odometer indicates any difference from the Trip.


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Old 15th March 2019, 15:46   #6
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Quote:
Originally Posted by slovcan View Post
Some time ago there was talk of legal action against car manufacturers based on "optimistic" speedometers (5%-15%). It was thought that the cars were racking up mileage to the maximum listed in the warranty 5%-15% quicker than reality and saving manufacturers money by the warranties ending early. It turned out that while the speedometers had that buffer to prevent unintended speeding, the odometers were accurate. How? I don't know. Measured against GPS? I don't know. Just thinking out loud.

Cheers,
Glenn
I think that you are correct.
When I had by digital speedo enabled, I noticed quite a difference between this readout and the analogue speedo.

My over-read on the speedo is approaching 10%, but I do not get those kind of discrepancies when measuring distances, with the odometer.




On the IPK Diagnostics on my car, I can get two different speed readings under 7.3 and 7.4. The readout is in km/hr rather than mph.
From what I can make out, the odometer and digital speed reading is the same as 7.3 and the analogue speedo is from 7.4.

I used the excellent guide from T-Cut here

Maybe something has gone wrong with the data on the OP's car.
I notice that 21.0 does a software factory reset in the event of a configuration error.
It might be worth trying that.
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Old 15th March 2019, 15:57   #7
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Speed displayed by default is faster than actually driven, as.mentioned above. Hence the phrase 'indicated speed' mentioned on police tv shows.

Mileage being displayed incorrectly is a separate issue and have no idea aside from what has been mentioned above regarding overall wheel circumference. In saying that, I would think 3 kms is quite difference over such a short distance. Although I wonder would the be a 10 per cent circumference difference between an 18 inch wheel tyre combo and a 16 inch?

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Old 15th March 2019, 19:47   #8
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I don't know what the regulations are in NZ, but my reading indicates that in Australia, Regulation ADR 18 says speedos cannot indicate less that the true speed, and over-indication accuracy is limited to a maximum 10 per cent plus 4km/h. This means that at a true speed of 100 kilometres per hour the speedo can’t be displaying 99 or under, but it could be displaying up to 114.
That sort of variance could probably explain the discrepency in travel distance as well.


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Old 16th March 2019, 08:57   #9
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Yes, but in LittleMan's case, he is getting an under read whilst measuring distance.

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Old 16th March 2019, 09:07   #10
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ŲCould you be suffering from an intermittent loss of signal from the front right abs sensor,?

Not enough to cause Speedo needle flicker and abs warning, but enough to drop the distance pulses counted,??


Do you have any warning lights or Speedo needle jumping??

You say it's a new car... does the ABS light cycle when you first turn on or has some scumbag blanked the led off,??
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