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Hi all

I've just purchased a brand new 2017 Giulietta, but the speedometer seems to be under-reading, specifically at low speeds.

With a reading of 70mph on the speedometer, GPS says I'm going 68 - fine.
With a reading of 30mph on the speedometer, GPS says I'm doing exactly 30.
With a reading of 20mph on the speedometer, GPS says I'm doing 26 - not fine.

I've tested this with a couple of GPS units, as well as the one built into the infotainment system. Even a roadside speed warning sign says I was going well over 20 when my speedometer indicated I was under.

Even the digital readout you get in 'All Weather' mode says I'm doing 25 when the analogue dial says 20.

Has anyone experienced similar/know if a fix is possible?
 

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Report it to the dealer - benefit of it being a brand new car. Then post back and let us know what they said.
 

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I wouldn't worry. Your sat nav isn't as accurate as you think as it is only accurate to within 10m in any direction - that's up and down as well as left right, forward and backwards. That means it finds it difficult to take account of incline so it could be ore than 10% out itself.....which is less than your speedometer error! I find the GPS reads about 2-3mph below what the speedo does, but then if you really want to know what speed you are going, you need something that is designed to measure speed accurately, not something that tells you where to go nor something that indicates what speed you are doing.
 

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I would just get a friend to drive next to you and see what his reading is while you're doing 20mph, if it's indeed off you should get the dealer to sort it.
 

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Might be my memory or me just being stupid but doesn't the G speedo increments change after 20mph? The first 20mph seems to be bigger than the rest? I'm going to have to check this I feel....

Sent from my Moto G (4) using Tapatalk
 

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Hi all

I've just purchased a brand new 2017 Giulietta, but the speedometer seems to be under-reading, specifically at low speeds.

With a reading of 70mph on the speedometer, GPS says I'm going 68 - fine.
With a reading of 30mph on the speedometer, GPS says I'm doing exactly 30.
With a reading of 20mph on the speedometer, GPS says I'm doing 26 - not fine.

I've tested this with a couple of GPS units, as well as the one built into the infotainment system. Even a roadside speed warning sign says I was going well over 20 when my speedometer indicated I was under.

Even the digital readout you get in 'All Weather' mode says I'm doing 25 when the analogue dial says 20.

Has anyone experienced similar/know if a fix is possible?
Fix = new dials.
 

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Mine is the other way around; it over reads. When on the northern A1 with the average speed cameras I set my speed on the cruise control at 54mph (within 10% of 50 limit) on my GPS/Sat Nav but the dial is reading virtually 60mph.
 

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Mine is the other way around; it over reads. When on the northern A1 with the average speed cameras I set my speed on the cruise control at 54mph (within 10% of 50 limit) on my GPS/Sat Nav but the dial is reading virtually 60mph.
I also tend to set my cruise control a bit higher than speed limit because of it and while doing this I'm slowly but surely overtaking pretty much everyone which means they all are set at speed limit but in reality driving below it thus all cars over read.

I'm sure it's the manufacturers being on the safe side as the other way around will get them in loads of problems.
 

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according to regulations, the car's speedometer is not allowed to indicate less then true speed, so they will always err on the plus side.

regulations:
European Union member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers[7][8][9] are similar to the UNECE regulation in that they specify that:

The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

aus:
https://www.racq.com.au/cars-and-driving/safety-on-the-road/driving-safely/speedo-accuracy
 

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Mine is the other way around; it over reads. When on the northern A1 with the average speed cameras I set my speed on the cruise control at 54mph (within 10% of 50 limit) on my GPS/Sat Nav but the dial is reading virtually 60mph.
Alfa says the gauge overreads by 6% + 1 kph. That of course will also depend on the tyres fitted and how much they are worn.
 
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