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Discussion Starter #1
While driving today, I had active Waze on my Verizon Iphone and my Navdy plugged into the OBD port.

The cars speedo says 52, Navdy and Waze say 49. I pulled out my old garmin, did it again and the Garmin also said 49 while the speedo said 52.

I know generally there is a +/-3% margin of error. But this is more than 3% it is over 6%. When I did the same things at 60, the speedo was saying 64, which is also 6%.

Logic says if the speedo has a 6% error so does the odometer which means it is reading 6% too high and my MPG is 6% worse as well.

Anyone else observe this?
 

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Mark, no offense but I hope all those devices were 'hands free' so that you were not distracted whilst checking your speed?
Generally, the UK police accept a 10% error in car speedometers, so a 6% error should be seen as acceptable in keeping you on the right side of the law. Not sure what US police forces will accept and whether it is standard across all states. Trust your F-Pace speedo. And of course, none of us are ever guilty of speeding are we?????!
 

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While driving today, I had active Waze on my Verizon Iphone and my Navdy plugged into the OBD port.

The cars speedo says 52, Navdy and Waze say 49. I pulled out my old garmin, did it again and the Garmin also said 49 while the speedo said 52.

I know generally there is a +/-3% margin of error. But this is more than 3% it is over 6%. When I did the same things at 60, the speedo was saying 64, which is also 6%.

Logic says if the speedo has a 6% error so does the odometer which means it is reading 6% too high and my MPG is 6% worse as well.

Anyone else observe this?
The police in America don't really care if there is a margin of error. Haven't you ever been pulled over or seen something on TV where the person says "well officer my car said I was going such and such speed" and the cop says "I don't care I got you at such and such speed, license and registration!!!"

Ive never experienced a car going faster than the speedometer indicated, but I guess there is really no way to tell. IMO the cars speedometer would be the most accurate over all of those other things.
 

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Discussion Starter #4
Assuming everything other device was correct, the car is going slower than the speedo says, which is what I would prefer. However, I am surprised at the error. That means when the Odometer says 20,000 I only actually drove 18,800. The value of the car is tied into the odometer and my car is artificially being depreciated more than I actual drove it.

Now imagine it was lease with 36,000 miles allotted. In actuality I drove 36,000 miles but the odometer says 38,180. Now I'd have to pay 0.25/mile for overage which would be another $545.

You'd think in this day of connectivity, sensors and GPS, the Speedo/Odo would be more accurate than 6%
 

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Assuming everything other device was correct, the car is going slower than the speedo says, which is what I would prefer. However, I am surprised at the error. That means when the Odometer says 20,000 I only actually drove 18,800. The value of the car is tied into the odometer and my car is artificially being depreciated more than I actual drove it.

Now imagine it was lease with 36,000 miles allotted. In actuality I drove 36,000 miles but the odometer says 38,180. Now I'd have to pay 0.25/mile for overage which would be another $545.

You'd think in this day of connectivity, sensors and GPS, the Speedo/Odo would be more accurate than 6%
I think it is, I think the cars systems are much more accurate than third party systems.
 

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I think we should have many more comparisons from other owners before we assume the speedometer is off on all by 6%. Isolated instances of problems have a tendency to get blown way out of proportion on this forum.
 

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As is the case in my 4Runner, radar detector gps, a phone-based navigation & mapping program and those fixed "you are going ## mph" signs all converge around speedometer measuring 1-2 mph over actual speed when I'm doing 55-60 mph in my F-Pace.
 

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I've compared my speedo (sorry, better edit that to speedometer before someone gets funny) to my Garmin and to Wave/Google Maps/Apple Maps on my iPhone, and the car is always within 1 mph of the stand-alone device. FWIW, I have 22/s on my F-Pace.
 

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I have been meaning to compare the odometer and speedometer of our 2.0D FP to a separate gps. Often the odometer and speedometer may vary each other by a few percent. Had a diesel Jeep Liberty that the odometer was about 5% less than actual and the speedometer was about 5% more than actual. Will check our FP on our next long distance trip.
 

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Discussion Starter #10
I think we should have many more comparisons from other owners before we assume the speedometer is off on all by 6%. Isolated instances of problems have a tendency to get blown way out of proportion on this forum.

Agreed, that's why I was asking to see what everyone's else experiece was.

I am on stock 19" (Premium model).
 

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I agree that the speedometer issue is concerning. However, on what basis do you think it definitely impacts the odometer reading. My understanding is that the odometer and speedometer operate wholly independent of each other. The odometer is based on the number of tire rotations to create the number of miles driven, but that it has nothing to do with the speed at which the vehicle is actually driven. I am far from an expert so others may very well confirm that my thoughts are incorrect.
 

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BMW does the same thing (I believe theirs is 7%). This is mentioned hundreds of times on bimmerfest.com and several other BMW enthusiast sites. It is an intentional error put in by BMW on the speedometer only, the odometer is on a separate measuring system. I am also pretty sure that the offset can be changed by coding the car - available to anyone but it is pretty complicated but can easily tune things like turning off the seat belt warning noise, setting the TPMs to display the pressure, enabling the auto up on windows etc.

I am new to Jaguar so I don't know for sure, but I'll bet that they are doing something similar.
 
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Since you live in NY @MarkF2 there must be radar detector signs on some streets somewhere that post your current speed. I would think they are very accurate and you can experiment without taking your eyes off the road and compare it to your speedometer.
 

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Since you live in NY @MarkF2 there must be radar detector signs on some streets somewhere that post your current speed. I would think they are very accurate and you can experiment without taking your eyes off the road and compare it to your speedometer.
Hey MKenM , how can you LOOK at that sign on the side of the road , "without taking your eyes off the road" ???
Just curious !!! ;)
 

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Discussion Starter #16
Next time I'm on the expressway with mile markers, I'll measure the odometer against 10 miles of mile markers to see if there is an Odometer error.

The problem with the speedtrap radar signs is that they are usually in 20MPH school zones, it would be too tough to measure a 6% error on 20MPH
 

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My speedometer is 2mph over at speeds ranging from 30-90 mph. Very consistent.
 

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I agree that the speedometer issue is concerning. However, on what basis do you think it definitely impacts the odometer reading. My understanding is that the odometer and speedometer operate wholly independent of each other. The odometer is based on the number of tire rotations to create the number of miles driven, but that it has nothing to do with the speed at which the vehicle is actually driven. I am far from an expert so others may very well confirm that my thoughts are incorrect.
But that's exactly how a speedometer works too.
 

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I know generally there is a +/-3% margin of error. But this is more than 3% it is over 6%. When I did the same things at 60, the speedo was saying 64, which is also 6%...
I would be inclined to believe the speedometer (within one or two percent?) over GPS. Your apps are all using the same GPS readout in the phone and they have to calculate speed from rapid instantaneous position measurements, each of which having errors at the centimeter to meter level. Depending on what the constellation looks like at any instant the errors can change. Same issues with the Garmin.
The best calibration is finding a measured mile marked on the highway (hold 60mph and measure the time), though I can't remember seeing one of those recently...
 

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My 2017 F-Pace S on 20" rims reads 4km/hr higher than actual. Most vehicles I've owned are 2km/hr over what I am actually doing...

A good article can be found here explaining why:

Why you may not be driving as fast as you think - The Globe and Mail

Basically the article describes that some countries have laws that a speedo cannot read lower than actual speed, so they build in the discrepancy to make sure that they cover any tire manufacturer with slightly larger diameter tires of the same size, over-inflation, etc... that would make the tire larger and thus causing the driver to drive faster than intended.

I'm hoping that the dealer can adjust mine at my next service, fingers crossed?

S.Chapman
 
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