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GPS speedometer and tunnels?

I just read a Norwegian review of the Model S, and noticed that the speedometer is GPS based.

How will this work in a long tunnel? In Norway we drill an underwater tunnel under every fjord we can find. One close to me is 6 km long, and pretty steep both up and down. Construction will soon start on a 14 km long one.

Will the cruise control be able to keep the speed constant if set before entering the tunnel?

The main problem here is that there are speed cameras in these tunnels. Both regular ones, and average speed cameras that measure the speed all the way down...

- Erik


I really doubt that it is GPS controlled. Much easier just to get the speed off the motor RPM or the wheel sensors. No gears to change so motor RPM unlike a car is directly related to MPH, assuming the wheels are not spinning.

More importantly, unless you have the Tech Package, you don't have GPS, so that would require two seperate ways of measuring the speed depending on Tech or no Tech package. I can't imagine they would go through the extra work.

What would be good is having the GPS know what road you are on, and looking up the local speed limit at that spot in the road, and using it for smart cruse. But again, you'd need the Tech package. Is it possible thats what the article is mentioning?


What leads you to believe it is GPS controlled?

This here article, which is in Norwegian, states that there is a "GPS based speedometer":

Good luck ;)

The journalist that wrote that article is wrong... :)

OK, I'll give it a go since I lived in Denmark for a year - twenty five years ago - on a study abroad year and Danish is close to Norwegian. The title:

Tesla Model S: Dette er en julegave fra norske politikere

Essentially translates to:

Tesla Model S (duh): A Christmas gift from Norwegian politicians

I imagine it is referencing the large tax incentives offered there to electric cars and so a car like the Model S is really competitively priced compared to luxury alternatives.

I know all Scandinavians know English better than we know any Norse languages, so please correct my translation if it's off.

Hej hej,


I doubt the speedometer is GPS-controlled, it could however be GPS calibrated automatically. That would be really nice, 100% correct speedometer all the time. Auto-calibration should be quite slow, averaging difference over several miles and slowly adjusting the speedometer until speeometer and GPS match.

@petersv +1

I don't even think in the US a GPS only speedometer would be legal. The car must have an accurate odometer and that can't happen with a GPS based system.

The Nav in my LEAF displays the local speed limit, but is not connected to the cruise.

By the way Tesla, the Nav is standard equipment in all LEAFs, as is SiriusXM Satellite Radio with a 3-month trial subscription to both their entertainment and traffic service. The traffic service is slick. Displays on the Nav map and you can also select a line item breakdown of traffic in your vicinity or along your intended route. You also get three years of free data connection with AT&T for the remote apps.

Speedo is NOT GPS controller. Anyone who has driven one and sees how quickly it updates/reacts to speed shows its being driven from rpm/techo sensor.

'Commercial' GPS simply is not that 'fast' at updating (deliberately - for military reasons.

I think I read that speedometer is GPS-calibrated but once calibrated it uses motor RPM to figure out speed. Calibration happens (or should be done) whenever you change tires and is one time thing not ongoing process. Can't remember where I got this impression though. Some post dealing with tire change I suppose.

Since the tires will rotate faster when they get worn I think the calibration actually should be an ongoing process. But since we charge tires two times a year here in Norway twice a year calibration would be good enough for me personally.

19" tire diameter is about 703mm. If you have worn 5mm off then track length changes from 2208.5 to 2177 (about). That's about one and half a percent difference, so instead of going 100km/h you are doing 98.5km/h. That's close enough for me, it would still be most accurate speedometer I have ever had in any car I have own.

Hm, that brings up an idea. With digital tech you could have a "zoomed" sub-speedo that showed the 5 mph bracket you were in, expanded into tenths of a mph, to give at least the illusion of precision!

With digital tech you could have [...] (Brian H)

In German we have a saying: "Du könntest Dir auch ein Loch ins Knie bohren und gucken ob Öl kommt." About equally useful.

Oh what fun it would be if the speedometer were controlled by GPS.

"Sorry officer, there must be a solar storm today."

There is zero need to calibrate this. No other cars do, why should Tesla when its a <1.5% difference.

Has it been an issue in any car ever? I say 'no'...

Think for a moment how any GPS calibration may work and you'll see its problematic. GPS simply is not accurate enough to make any calibration. Remember that when you're driving in a straight line even with 6+ satellites the accuracy is still -/+ 3m typically which is probably a higher margin of error than the circumference difference in a tire.

More humorlessness? It was an example of excessive precision "for fun".


A google search leads me to believe gps speed is more accurate than regular speedometers. I've noticed my wife's speedo differs by about 4 mph from gps speed readings on the highway. Could be the difference between a ticket and not.


1. Nobody else does this. It could be another Tesla first. I would really appreciate it. It is a simple software function.

2. You average the difference over several miles, any errors should cancel out. And GPS is more accurate for speed than position anyway. The speed is not derived from distance/time only but also uses doppler shift.


Your wife's runs 4 mph off at highway speed. Does it vary by speed? Say, is it 2 miles off at half highway speed? Or pretty much off 4 mph at any speed when moving? I'm curious, because over the last 12 years I've come to adjust to the fact that my car seems to run 10% off at any speed as measured by the various radar signs at different speeds I see on the road. Now when I'm on a 40 mph road for example, I lock the cruse on 44.

I think on my car, the spedo cable is "adjusted" by interchangable gears depending on tire and (possibly) rear differential gearing optons.

Bottom Line: If the speedometer is GPS based, I'm out. I simply won't buy one, because THAT singular fact would indicate to me that this is a full-blown tracking device. While I am a law-abiding American, I am tired of what has been happening to the FREEDOM and RIGHT TO PRIVACY that the US Constitution promises us. That includes the Second Amendment and all of the rest of it. It shocks me that in as little as 12 years, the politicians and schemers of the world have successfully plotted through "The Patriot Act" and a variety of other abused legislation(s) to take away our Freedom. I am very much PRO TESLA as well as a huge advocate of the science behind Nikolai Tesla, but I am very sure I'm not going to buy one big dang tracking device. Track the non-Americans. Track the Terrorists. But don't water my leg and tell me its raining.

I hope that person is wrong, but I will never participate in that kind of a product. I'll be checking into this further.

@TV - I assume you don't carry a cell phone then correct?

And they constantly stream rearview camera feed (camera on display or not) back to mothership (and big brother). And heaven forbid if any 2nd Amendment articles are placed in the frunk - GPS location and reaview view stream go straight to ATF central as part of their big data repository. All good though - nothing to fear.

TV, careful there - your post could be used against you in a carry permit hearing. Just sayin, as a carry permit holder in both MD & VA, those kinds of rants can come back to haunt us "right-wingers"

@TV Bottom Line: If the speedometer is GPS based, I'm out. I simply won't buy one, because THAT singular fact would indicate to me that this is a full-blown tracking device.

GPS is not two-way communication. Car doesn't have to tell anyone where it is to get GPS coordinates and use them.

Your cellphone OTOH does have build-in tracking. Also pretty much any credit card, RFID toll systems etc. keep track on where you go and what you are doing. Your web traffic is being monitored, your Google searches are being registered etc. etc. etc.

Not by government (unless you are in some list) but by corporations which use them to target advertisements, spam you and so on.

If you want to avoid that stop using money and any modern communication device, never buy anything and move to nearest forest so that there are no security cameras watching you. In fact you need to move away from society completely, because your friends are being watched and that leads "them" to you.

@TV - you do know that GPS is receive-only, right? The GPS receiver picks up broadcast of timestamps from a number of satellites, it knows the orbits of those satellites and can determine where they were at the instant they transmitted the signal, and by calculating the propagation delay from each of them it establishes a 3D position and error bounds (since the propagation speed of radio signals varies with atmospheric conditions). So, the fact that GPS is on in your car doesn't say anything about transmitting your location to anybody.

If you care about that sort of thing, what you should be worried about is your cell phone (and the cellular modem in the car), since its very operation requires that the cellular company have a rough idea of where you are at all times. And certainly don't run Google maps, since it will be sending your location to their servers in order to get the right map tiles.

Aside from that, I would be exceptionally surprised if the speedometer were GPS based as it is a lot more work, uses a lot more power, is unreliable in city canyons due to multipath and lack of line-of-sight to the satellites, etc compared to just measuring how many times the motor turns (which already has to be known to properly control the AC induction motor).

However, I am guessing none of this explanation matters to you because you don't seem the type to let facts get in the way of your righteous outrage.

The Patriot Act is indeed a horrible piece of legislation, but it has nothing to do with why GPSes are in cars.


I suspect that TM can indeed determine the location of every car at any point in time, so long as it has an internet connection. We know TM can log into the car remotely, and its GPS coordinates would surely be available along with myriad other data. I'm pretty sure that the speedometer is NOT GPS based.


Just because the speedometer is not GPS based does not mean they are not out to track you.

@DouglasR, as you point it out, you need that internet connection for that to happen. GPS by itself does nothing like that.

When cell phones went digital, they needed to send packet data so multiple calls can share one radio frequency via time slicing. In order to make sure packets don't collide, phones exchange timing signals from the tower. It's a function of the speed of light, and the frequency of time slicing.

With one tower we know you are in a circle with a hundred yards or so, more or less. With two towers, we have an intersection. Chances are in most places, you'll be in sight of several towers. The network then knows your location to about 50 feet with triangulation, and without GPS.

So TV, it has nothing to do with the car.

We did notice what you had for lunch today, and you might want to consider your salt intake. Also, we noted you did not floss last Tuesday. Finaly, that thing you were considering you told no one about? I wouldn't, if I were you. I'm just giving friendly advice.

Just looking out for you as allways,

Your Big Brother