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arquiella

GPS: Garmin 3790T







Post Re: car speedo might be off     
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The speedometer on my car also has a lag of 4 to 5 km/h with respect to pointing my GPS navigator. I guess the car manufacturer to make it easy drive to the speed limit is not exceeded when GPS is not available.
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trevorap2002

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Post Speed descepancies     
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All modern cars have their speedos calibrated at a lower speed, by manufacturer, approx. 5% of actual speed as a safety margin against speeding offences per National Design Rules. Anyone clocking over the speed limit is unable to claim inadvertence as at say 100 kph they would have their speedos showing at least 105+ proving an intent to speed. Although subject to a slight tolerance, also to the negative, your GPS would be the more accurate. Your odo should still be accurate as per manufacturers spec or they could be accused of fraudulent practice. Any discrepancy beyond that is due to non manufacturer spec with regards to wheel diameter.







johmazz2006

GPS: Garmin Nuvi 765, Garmin 3950LMT, Garmin 2455LMT, Navman40, Garmin StreetPilot 3







Post Re: Speed descepancies     
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trevorap2002 wrote:
All modern cars have their speedos calibrated at a lower speed, by manufacturer, approx. 5% of actual speed as a safety margin against speeding offences per National Design Rules. Anyone clocking over the speed limit is unable to claim inadvertence as at say 100 kph they would have their speedos showing at least 105+ proving an intent to speed. Although subject to a slight tolerance, also to the negative, your GPS would be the more accurate. Your odo should still be accurate as per manufacturers spec or they could be accused of fraudulent practice. Any discrepancy beyond that is due to non manufacturer spec with regards to wheel diameter.


That is incorrect. I have a Toyota Prado 2003 model and the speedo is exactly the same as 3 different brand GPS units T all speeds.
Wife has a Suzuki sx4 and speedo reads 8 kph more than actual.
The discrepancy levels in speedos should be forced to be exact in modern vehicles in standard delivery trim when new by law or not allow vehicles into the country until they meet the regs.

No excuse for inconsistency in the digital era.
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rjscooke3

GPS: Garmin Nuvi 760 & Nuvi 260wt







Post Re: GPS Speed disparity     
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johmazz2006 wrote:
rjscooke3 wrote:
This is all subjective i believe for several reasons on unless you have your car speed tested at a recognized testing facility you would not know if it reads right or not. Secondly I doesn't ever remember reading any data from Garmin as to the accuracy of there units, nor do i ever expect too.

Regards Russell


Good for you Russel... Think I would rather trust a GPS's speed reading over a suspect speedo reading, if there was a discrepancy between the two, as it does not seem to matter what brand GPS you take a reading from, they all seem to come up with the same results.


Thanks for the insight johmazz2006 if you ring Garmin or any other manufacturer I am certain they will be able to explain why when we have less satellites to use than for example than the usa, why speed reading are indicators only. As explained to me from Garmin the math's says more satellites more accuracy.
Hence the warnings in the box to not rely on speed / map data we are the humans.
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royjordan

GPS: Garmin Nuvi 2597 LMT







Post Re: GPS Speed disparity     
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I upgraded my Garmin to a newer model and taking it for a test drive the first thing I noticed was that my speedo is slightly higher than my gps shows..... about 5km/hr .

The way I look at it is that satellite technology is way more advanced than my 1990 car so I always trust what my gps tells me.

However...... when I am approaching a speed camera I always revert to what the speedo tells me as it is better to pass a speed camera in a 60 km/hr zone doing 55 km/hr

Roy
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E240

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Post Speedos and Garmin; which is accurate     
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I have a Merc E240 1998. The speedo reads 3+ km/H lower than the Garmin. 2 questions. which one is accurate? How do you calibrate the speedo?

Regards
E240





msh370

GPS: Garmin Nuvi 265W







Post GPS Speed disparity     
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I've used my Garmin Nuvi 265W and my mates Tom Tom in Ford Mondeo. At exact 100km/hr on my speedo, both read at 98km/hr. I also passed a mobile speed monitor which read 98km/hr. So I knew my cars speedo was 2km/hr lower. Most manufacturers make sure that your car's speedo is not at exact speeds. However, I always pass a speed camera below the posted speed limit to ensure there is no error in reading by the camera itself.
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rodney_button

GPS: Garmin Nuvi 855, Garmin Nuvi 2797







Post Speedos and Garmin; which is accurate?     
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I have a 2000 Mitsubishi Pajero and the GPS indicates that the speedometer shows approximately 3km/hr faster than the GPS speed.
When travelling back from Geelong one day I compared the freeway roadside vehicle speed indicator against the GPS and it was spot on. Tyre size and tyre wear can be contributing factors to speedometer inaccuracies.
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sw8490

GPS: Garmin 650,2595,1490,205,255w,250w,52 nuvi Magellan mastro 3100







Post Re: Speedo Errors     
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asalmon3 wrote:
Not sure where of 5% on car speedometers. If you can find a review on the NRMA (RACQ, etc), they usually tell you what the error is for that car.

My 2006 Mitsubishi 380 is doing 95 when 100 is displayed on the speedo. This is EXACTLY what both my CoPilot and Garmin GPS units indicate.

I usually drive to the GPS now.

Cheers!

I had the same issue, so we actually had use of a radar gun to actually clock my truck and we found the Garmin was a lot closer to the actual speed. gun was county police and verified. So I now go by the GPS. For what I know is the closer true speed
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diver_318

GPS: Garmin GPS MAP76s & Garmin Nuvi 3590 LMT







Post GPS Speed disparity     
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You should do the same check between GPS and speedo when you change tyres as well. I have noticed a considerable difference when the tyre profile is changed (therefore the distance covered on the ground for 1 revolution of the wheel). It can be 2-3 kph between the tyres when new and then when they are worn. I drive by GPS these days unless in tunnels. Cool
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william.beck

GPS: 1490T







Post Speed     
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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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linghams

GPS: Garmin







Post Speed disparity     
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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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pira 999

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Post Re: An Occasion when a sat-nav could be sadly wrong     
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billynibbles wrote:
The hypotenuse of this triangle would represent the road surface on the slope, so therefore for every 1 meter travelled across the surface of the Earth (the base of the triangle), 1.414 meters have actually been travelled by the vehicle on a sloping road. Thus if travelling at about 70 mph (or kph), the sat-nav may well be telling you that you're only 'doing 50' as this reflects your horizontal speed.

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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