[Mullet]

Took the i30 up the highway on Sunday and threw the GPS in for good measure . What i noticed straight away was the speedo on the car vs the gps was out by about 10% .When the cars speedo said 100 klm/hr The GPS said 92klm/ph. When the GPS said 110klm/hr , the car was doing about 120klm/hr. Any body else come across this .

[Lakes]

yes m8, i checked with my GPS but don't think mine is out by 10%, that is one reason why police have to alow a margin of error with there speed camera and radars as most car speedo's are out. NSW are supposed to allow 10%, VIC only allow about 2%. while i was in Adelaide i read there police want to keep the margin there a secret
but when traveling i use my GPS as can travel a small amount faster an know you should be safe.

[Seoul-mate]

Yeah Mullet, sounds about right from my experience. And from what I know there is no-one in the owner's club saying their speedo is
spot on for accuracy when checked against their GPS.

This topic was discussed at length some months back (on the Hyundai forum I think, but I have just looked there and can't find it now).
Anyway I recall the consensus at the time was that regulations require that car makers are not allowed to make speedos that read over-speed so
they tend to err on the side of caution so produce them reading under-speed by a good percentage.

[Thumper]

Yeah, I've mentioned this before, mine is 7km/h out at 100km/h (But the trip computer is spot on, go figure)

So when my speedo shows 100km/h I am actually doing 93km/h (According to three different GPS devices)

[Mullet]

How acurate would the gps be ?

[ozsnowman]

been through the speed traps on both the Hume & Calder higways here in Victoria, and they were both around 6km/h out

[i30Dave]

Tested mine out today from Bordertown to Adelaide. The i30 speedo
was only out by 2-3k's. I use a Navman S90i GPS

[i30manUK]

Manufacturers tend to make sure their speedos err on the side of caution, so they can't be taken to court if you get done for speeding  

[Lakes]

If you fit a larger turn, tyre or tyre and wheel combination, that will slow your speedo down and also your Kilometer or mileage will show less too, my GPS is a Garmin (if that matters) it reads out digitally the speedo is small scale clock type so hard to compare, the GPS also showed the trip is slightly fast so they will be happy about that at the dealer as will get there servicing $ faster  when i go away next i'll set Cruise control and check speedo more carefully.