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I have noticed that when I look at the speed on the Sat Nav it is always slower than the speed on the Speedo. Then, when passing speed signs in certain villages (the ones that show the correct speed or lower in green but red when you go over the limit) that they read the same as my Sat Nav. Which is more accurate? My son, who is a mechanic, says that the Sat Nav is more correct because it is based on actual speed and distance travelled. If that is the case then my MPG is actually higher than I thought by more than 10%. I wonder is this is because the speedo is for all models no matter what size wheels you have. Any of you boffins know the answer to this?
 

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PHEV 2018
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I have noticed that when I look at the speed on the Sat Nav it is always slower than the speed on the Speedo. Then, when passing speed signs in certain villages (the ones that show the correct speed or lower in green but red when you go over the limit) that they read the same as my Sat Nav. Which is more accurate? My son, who is a mechanic, says that the Sat Nav is more correct because it is based on actual speed and distance travelled. If that is the case then my MPG is actually higher than I thought by more than 10%. I wonder is this is because the speedo is for all models no matter what size wheels you have. Any of you boffins know the answer to this?
 

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PHEV 2018
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By Law in the UK all speedos have to read between exact and 5%fast.

So all manufacturers set them slightly fast.

The GPS in your phone or tablet will be more accurate.
 

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IONIQ Electric, SE (w/ CCP) 2018.
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My 2018MY IONIQ 28kWh consistently reads about 2 kph faster on the dial than GPS. Funny though, if I use the digital speed display on the the right of the speedo, it displays the correct speed.
 

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When I drive by one of those police speedos, it says I'm going 30 mph and I look down and my speedo is right on the 30. Accuracy may change at higher speeds.
 

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IONIQ Electric, SE (w/ CCP) 2018.
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When I drive by one of those police speedos, it says I'm going 30 mph and I look down and my speedo is right on the 30. Accuracy may change at higher speeds.
I think that the North American speedo is very accurate.
 

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It is interesting that in all the other cars I have tested, OBDII speedo signal is almost as accurate as GPS (I would say it is more in some areas). For me it was shocking to know that the car knows the real speed (for abs, esp etc) but still lies to me. In 38 kWh 2020 Ioniq, I am not able to get that PID.
 

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UK spec 2020 1st Edition in Polar White
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This is interesting, as an earlier contributor said, Speedo accuracy (or lack thereof) is mandated by law here. Driving at an indicated 30mph the roadside signs usually say 27 or 28, if your car is the other way around, then that’s a problem, here at least.

To pablo_fil, your cars have always lied, I think you will find the UK law is based on an EU directive to which Spain is also required to comply.
 

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That's contrary to my experience in the UK where if the roadside speed would measure 30, my speedometer will show 27mph.
Same here, my 2020 hev is reading 30 mph on the Speedo when the GPS speed readout on the infotainment map screen is only showing 27 mph.
 

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Ioniq 2020 38KWh, VW Passat GTE, Toyota Landcruiser, Alfa Spider S2
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Ioniq Is almost exactly 10% over-reading. 30 shows 33, 50 shows 55 etc.
 

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My North American model was also spot on in agreement with radar warning and nav sat speeds, but starting with 20,000 miles on the OEM tires it read about a mph faster. Now with 40,000 miles on the OEM tires, it reads about a mile and a half faster. As would be expected with now slightly smaller wheels having more rotation per mile. Most US cars I've had read 2-3 mph faster than actual. I also have a Honda motorcycle that is spot on and somehow (and most surprisingly) tire wear has not affected the accuracy (now on second set of tires).
 

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Ioniq Plug-in Hybrid Premium SE Polar White purchased new March 2018
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After the recent software updates, there is an accurate speed display on the map screen. Reading on the speedometer is 10% fast. Travelling at an indicated 70 on the speedo is an actual 63mph. UK
 

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Ioniq EV Premium SE 38.3kWh 2919
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I have noticed that when I look at the speed on the Sat Nav it is always slower than the speed on the Speedo. Then, when passing speed signs in certain villages (the ones that show the correct speed or lower in green but red when you go over the limit) that they read the same as my Sat Nav. Which is more accurate? My son, who is a mechanic, says that the Sat Nav is more correct because it is based on actual speed and distance travelled. If that is the case then my MPG is actually higher than I thought by more than 10%. I wonder is this is because the speedo is for all models no matter what size wheels you have. Any of you boffins know the answer to this?
The last few cars I've owned in the UK have always shown approximately 2mph above the actual speed (as measured on a mobile phone GPS) including my latest ioniq EV. At anything from 30 to 70mph
 
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