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| Posted by steven.chaffer3 GPS Speed disparity My Garmin Nuvi 1390t consistenlty shows my speed to be 5% lower than the speed the car's speedo is showing. At 100 km/hr on the car's speedo the 1390t is showing 95 km/hr. Several times when this is happening I have checked the satelite screen to see the accuracy which has always been at 3 metres. By my reckoning, a 3 metre error in a km (1000 m) is 0.3% which should amount to a 'error' of 0.3 km/hr at 100 km/hr, effectively zero. I can't believe my car's speedo is 5 km/hr per out. (However I will check it next chance I get.) Any ideas about what is happening? Cheers Steven |
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| Posted by nimadude car speedo might be off You know your car speedo could be showing more than the real amount.. I know thats the case with my car - every time I pass one of those cameras that tell you the speed ur going (they dont take picture, just warn you), it shows my speed 5-10km/h lower than what my speedometer shows.. how old is ur car? |
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| Posted by steven.chaffer3 GPS Speed disparity I have a six year old Subaru Forester. I would have thought it was unusual to have a modern speedo out to that extent. I guess I was curious to know how accurate the GPS speed data is. Cheers Steven |
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| Posted by GDT More... Some posts are not listed here. See all posts here: GPS Speed disparity GPS Data Team |
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| Posted by william.beck Speed One way to check you Speedo is to make note of some of the 5 k markings on some of the expressways, will soon tell you if your Speedo is measuring distance correctly, especially if your tyre size has changed. I tend to trust the Garmin more nowadays |
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| Posted by linghams Speed disparity I thought it worthwhile to let people know that not ALL speedos read slower than the GPS - we have a Patrol which we bought new, and right from the beginning the speedo has been showing SLOWER than we are doing according to the GPS (both the old Nuvi and the new one we have just bought). Luckily we found this out pretty quickly or we could have been in serious trouble. The speedo is about 5km slow, and checking distance travelled by the markers on the side of the road we go about .5 of a km less in 10km. We recalculate distance to get a better idea of fuel economy but it is hard not to drive to the speedo when the GPS is not on. We haven't changed tyre sizes or anything like that. As I said, the car was brand new, straight off the ship. |
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| Posted by pira 999 Re: An Occasion when a sat-nav could be sadly wrong
Brilliant explanation thank you, and I'm sure this is the best explanation for the varied diffs between our Garmin & speedometer - it varies between 4 and 8 % & I could never understand till now why it varies. We stay in the hilly area just outside Bonn. So add the tyres & the built in safety margin mentioned, and it's all clear. Just for interest, we have 30km/h limits in the German Villages here, sometimes 50km/h- the grace % is 5%, so you get ticketed at 32km/h. In South Africa the normal town limit is 60km/h, and you get 9km/h grace; 10 over and they nail you. |
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