Anyone else seeing discrepancy between the gps speed and their speedometer? My 350h has stock 20” wheels, but it seems the speedometer always reads low compared to the GPS on maps. Sometimes up to 10kph. I’d have thought with stock wheels and tires the speeds would align properly.

 

I just drove my '22 350h along the 407 from Hamilton to Whitby (approx. 60 miles of 80 mph driving) and chose to use Google Maps as it's recently been updated to show speed as determined via it's GPS signal. My displayed speed on my centre display was no more than 1 km/hr faster than GPS figure at all times throughout the drive. Now back when I had a TomTom gps a few years ago, it needed a steady clear signal to the sky, high rise buildings and other structures that prevented a clear sky view always threw it off. This would be the only thing that comes to mind. I'm assuming you're thinking it's the car's speedometer that's off and not the GPS. If so I would take it back to your dealer as this needs to be addressed, and it would surely be covered under your warranty unless you're over 80,000 kms.

Of note as well, you're cell phone reception could also possibly mess up the speed display if you're have a poor signal, the app would try to extrapolate your speed possibly under these conditions. Normally I would trust my car's speedometer reading, and yes manufacturers always underrate the speed slightly in cars, been doing it for many years, provides driver with a bit of a overcompensated speed to err on safe side of 'speeding' scenarios.

I tried this out specifically to see the comparison myself between both speeds displayed, because a good strong GPS signal is very accurate at determining your rate of speed, if you have a good strong signal.

 

Most speedometers read slightly high by design. I've not really compared it to GPS, but around my area there are many speed readout warning signs. I go thru 3 to 5 each day. They typically show my speed 1-3 kph less than indicated on dash.

 

Thanks, I wasn't sure if it was because the stock 18" and stock-upgrade 20" had different rolling diameters and the difference was normal. Will bug dealership, car has just barely crossed 10,000km.

 

Did you ever get a resolution for this? I just purchased a used approved NX from a dealership, less than 20k miles and I’m finding the same issue. Waze shows me doing 65mph but the speedometer shows me doing only 60mph.

 

For me no. I now own an iPhone Air with the latest chip, and still have the phone based GPS apps showing a few kms per hour faster. Even when I'm clearly on 5G too. Glad it's showing a faster speed and not a slower speed, I could end up lightening my wallet in those circumstances. .

I've clocked my speed when going through those sign based speed zone radars and they're telling me same as my speedo. I do know vehicle speedos are intentionally set a couple of mph / kph slower, I'm sure for legal reasons. I've done the math with optional tire sizes available following manufacturer sizing and when you see the overall diameter or circumference there's almost no differentiation, so they've done their math correctly, you're not gonna get anything significantly different from your speedo unless you go way off script from the manual's acceptable tire sizing.

 

On a related note, I wonder if the distance travelled as shown on the odometer is just an AUC of speed multiplied by time.
I am saying this because the distance from the gas station (that I fill up in on my way home) to my home is always 5.5 miles on both my other cars (I always set my trip odometer to zero at fill up) but my NX450H+ always shows 5.3 miles for the same trip.
If the odometer calculation is speed X time, and the internal clock is accurate, it would imply that the speedometer is too low (not too high) by about 3.6% in my car. So for example when the speedometer shows 65 mph, I am actually going 67.5 mph. I should check this with GPS, but I have not done this yet.
BTW,, I am on factory tires and this has been the case since day 1.

 

Typical determination is done by a means of determining the wheel rotation accurately. The vehicle will never use any source of time at all. It's too far out of their control to remain accurate over the life of the car or under certain power supply issues. Cars can continue to run down the road with a broken alternator and only 9 volts coming from a worn out 12 volt battery. Your clock may not be accurate at that point. This is accomplished by using the abs system monitoring wheel rotation with a sensor pickup and a round cog gear like hub found on back side of wheel assembly. It simply counts the pulses and from a predetermined factor it figures out how much the car has travelled. Other options would be a pick up point from an internal driveshaft or transmission sensor, both of which will also be counting the rotation. The calculation involves the expected known circumference of the factory tire size spec'd for the car. Most manufacturers err on the low side so it's a little less. This is same system that calculates your speed as well. While tire sidewall profiles can change from options for a model offering lower profile tires, the actual outer circumference is unchanged. Possibly your other cars have strayed from the OE setup of tires or that manufacturer is using a different 'factor' so it's off a little from a comparable other car's reading for similar distance. It could even possibly be from reading the electric drive motor rotations on the hybrids. Keep in mind the legal ramifications of a manufacturer being too accurate and people suing because they claim the car is clocking up more miles than the truth so now they've lied to you and your car actually has less miles than stated, or was going faster than the speedo said. Litigation is costly, people like to sue big brother.

True GPS signal is not an easy get here too. Cell phone driving apps use GPS signals but at times under certain conditions are challenged to remain very accurate. Read this article below:

https://crawler.woehler.de/web-pulse...by%20the%20law.

 

You are right of course, I was overthinking it.
However, after comparing several trips where I compared the Google maps distance with the trip odometer distance, I am convinced that my other cars (Camry, Fit) are more accurate. The NX is doing the revolutions to distance conversion wrong and under reporting distance driven.
Coming back to the topic of this thread, I need to figure out whether this indicates that the speedometer (also related to wheel RPM) is correct or not.

 

Good luck with that. I don't think you have anything at your disposal to confirm an exact distance measurement over a large distance. Every device will always have some sort of acceptable accuracy to it, errors always exist, it comes down to how accurate is acceptable. All automobiles components are made to an acceptable level. I know from experience that the devices the police use for radar have to be calibrated daily before they are put to use each day, at least here where I live. And that certification of tested for accuracy is used in court to defend the police readings. You don't have any comparable fact to prove to the court how accurate your speedometer is in your defence. That's why speedometers are generally generous on their readout, meaning when it says you're going 60 your probably going 58. I wouldn't think Toyota would intentionally underestimate the travelled distance by much at all, since this distance would be used to calculate the gas mileage and to that end it would lower the results making the fuel consumption per mile look worse which would mean the EPA would get more money from them.

Here's a link to an SAE (Society of Engineers) paper recently describing their accepted current standards, which was updated in 2022.

https://wiki.unece.org/download/atta..._UN.pdf?api=v2

https://www.sae.org/standards/j2976_...ghway-vehicles

 

For my 2022 350h with 20" wheels, Google Maps shows about 3mph higher than the speedometer...going North-South. It's only about 1mph different going East-West.

I have always used Apple Maps for navigation, but recently switched to Google Maps when driving for work, so I just noticed this within the last few weeks. I would rather not use Google Maps, but Apple Maps has no way to upload several hundred locations at once.

Side Note: Google Maps and Apple Maps seem to be pretty much at parity, except for one item where Google Maps fails miserably. In Texas, most freeways have access roads on one or both sides running parallel to the freeway. You exit to the access road to get to cross streets, shopping centers, etc. The freeway exit signs will show the exit number and cross street name - "Exit 45 Main St." Apple Maps mimics this. In most cases Google Maps simply says to exit to "I-35 frontage road" and gives the distance to the exit. It does not show the exit number or street name. Very frustrating.

 

Google maps is always a little higher with speed displayed compared to my speedometer too. I thought it was due to my older iphone. I have a new Air now and nothing's changed it's still displaying a little faster speed, about 2-3 km per hr.

 

There is something wrong with Lexus and Toyota CarPlay implementations. Google Maps always reads faster than the speedo and at time I see gaps as big as 7–10 km/h in readings. The map accuracy on both Google Maps and Apple Maps is also horribly inaccurate. There have been many instances where I’ve done a turn and the maps shows me continuing forward or it’ll show me as having crossed an intersection and change my route when I’m waiting to turn.

I also have a Google Pixel work phone which I tested and it has no such issues with Google Maps. I also test drove a 2026 Jetta recently and also had no issues with CarPlay. And another anecdote on top, I took an Uber in a new Camry and saw that the drivers CarPlay maps did the same thing that my Lexus does with the speedometer and route change issues.

Personally I am convinced this is a Lexus and Toyota issue.

 

I've seen this on many different cars, even stand-alone GPS devices. This is the software on your phone trying to compensate for GPS inaccuracies. At best a consumer level GPS signal is accurate to, say around 5M which is the better part of an intersection, at best. Often, GPS signal can be degraded by localized interference where accuracy can fall much lower than that. It is also dependent on how many satellites the device can read, takes a minimum of 3 but for good accuracy 5 or 6 are necessary. Even military grade GPS signals can suffer from issues too, perfect example from a few years back when Iran stole an American surveillance drone by spoofing GPS signals to it and making it happily land inside Iran thinking it was returning to home base.

Anyway, the mapping software on your phone compensates for this by making assumptions and using statistical analysis of recently received data. It assumes you're actually on the road, and it assumes you are following the guidance route (if set), and generally uses its statistics of recently received data to try to guesstimate itself out of those inaccuracies. So when you turn (or don't turn when you should have), the software for a moment or two follows its assumptions rather than actual GPS data thinking it may be an anomaly, that is until it sees enough new data to revise its assumptions.

My wife and I share each other's locations with Google Location Sharing. Sometimes when I check where she is, it shows a radius as large as a hundred meters because her phone just doesn't have a good GPS lock, and then other times it'll pin point her to a particular room of a building. In that case, because its not using active guidance, fewer assumptions and therefore the inaccuracies are more visible.

 

Don't you hate it when your drone gets drunk and ends up at the wrong house .

Simply design engineering at work here. Buy an electronic device and expect it to do hundreds of different actions constantly and consistently well. You end up with actions that are acceptable for the intended user. I usually always end up at my intended destination with today's GPS mapping software. Will a cell phone locate a penny on the ground when you send the coordinates for it to your phone, probably not. But I can find the hotel I was looking for!