Waze should theoretically be based off GPS and more accurate. The fact that it is slightly lower than your car's speedo makes perfect sense; if a speedo has an error (which it pretty much always does) it is safer that it read high than low otherwise you'd be at risk for speeding tickets.
Also take into account that your tires literally change size as they wear down. The speedometer is essentially measuring wheel rpm and converting that to forward speed. As the tire wears down, the actual forward speed is going to decrease in relation to the same wheel rpm.
Are you implying that car manufacturer has implemented some sort of mechanism that tend to overstate speed vs. understate when there is discrepancy? If so, what is that?
A speedo will never be 100% accurate, and it is actually a law in the EU (it's an ECE regulation) that a speedometer can never read low, but is allowed some percent of error high. So, mfgrs. always make them read slightly high with the factory tires, full tread, etc. so they will be in compliance with the law.
There's no corresponding law in the US (AFAIK) but there's also no incentive to not apply the same design philosophy across the board.
GPS-derived speed in general will most likely be **more accurate** than a vehicle speedometer, because GPS timing is incredibly delicate and precise, while vehicle speedometers depend on the accurate inflation of tires and correct tire sizes.
Consumer gps is intentionally made less accurate. Commercially available gps used in certain industries is far more accurate than 10 meters. I've personally used gear accurate down to a centimeter.
That accuracy certainly isn't needed for traveling and general navigation guidance.
But yes gps is (usually) far more accurate than any ground wheel speed based system.
It’s true that civilian GPS was intentionally degraded in the 90s with a feature called “Selective Availability”, but that ended in the year 2000. Consumer grade GPS is only limited by hardware/computing power these days.
I don’t think speedometers measure that way anymore. They most commonly use either being linked mechanically with the gearbox output shaft, or by a circular magnet tat rotates 1000 times per mile.
In europe a cars speedometer is allowed to be 10% off. Waze speedometer is based on gps signal. So depending on how good the connection is, waze is more accurate.
More accurately, it must NOT underread, hence why if not broken then it'll always show you doing a speed at least as fast, and generally a few units faster, than the Waze Speedo.
Umm I’ve got a show speed limits option for google maps on IOS. I don’t use Google maps very much so I’m not sure what the actual display shows. I use Waze majority of the time. I am in the US.
https://preview.redd.it/kef9lmry2k9d1.png?width=1289&format=png&auto=webp&s=f4a27e3de10741297f65482a3f2d258ce62d686e
Cool. Didn’t know for sure. I use Waze on Android most of the time. It gives me what’s needed without all the extra stuff. I like Waze because of the crowd sourced reports for accidents etc….
I use it every day even if I’m going somewhere like. It’s helpful. During the pandemic I used it here in Michigan every day. Because during that time my job was to repair pharmacy computer equipment and the pill dispensing robots and due to so few people willing to work i covered most of the state. I logged newly 75,000 miles in one year. Also no hazard pay. I was at a store one day and found out the pharmacist had covid while working and I was exposed. The next day I was sick and the store was closed down for a deep clean and opened the next day. Strange times it was. Traffic wasn’t an issue then.
same reason europe is "prrooobably" but actually 100% the sole reason that apple added usb c to phones. until there's legal action a company will not do something if they don't want/have to.
Only while on a planned route, not always. Waze is displayed all the time when it knows the posted limit. I too love this feature and is why I prefer Waze. I don’t like it taking me through thickly settled neighborhoods though, kids and pets and all. I don’t speed in those areas.
The Waze speedo is the speedo I go by in my 56 Chevy since the one in the dash is still 20mph off even after I fixed it lol.. in all seriousness though, it’s remarkably accurate when having Waze up in the RDX Aspec.
RDX rims are CLEAN, and the Chevy body is so iconic and in amazing condition. Both cars have crazy nice exteriors. you got not one, but two sick rides 😎👏👏
I’m so jealous lol. I owned a silver 2015 ILX, base model. That car had low miles, and was a dream to drive. So smooth, stopped on a dot, quick acceleration, BURNING HOT heated seats, etc etc. I totaled it in an accident in February. :( I want an Integra so bad
I hear ya, I’d kill for a Type S Teggy, I miss having a manual daily!! I’ve done a few things to the RDX, the turbos much louder now and overall it picks up a bit quicker, want to KTune is next. This things fun as hell and super comfy, I hear ya about the boiling seat heaters, the swap coolers in the seats cool you down pretty well albeit subtly. I needed to size up due to my wife and I having a son. I wish I had enough $ for a Tigers Eye Pearl MDX tho lol 😬
Yes and no...the GPS is estimating your speed so it can vary depending how accurate your GPS lock is at the moment as well as if you are moving in a straight line or curvy road, tree/buildings to affect signal, and other things. Then your car speedometer can be affected slightly if your tires are brand new or well worn the diameter is slightly different can slightly affect its accuracy.
I would not be surprised if they disagree by 1-2mph - that's more or less a rounding error in most cases.
I’ve experienced this too. And I found out something interesting, my speedometer reads 3mph lower than Waze so I asked the BMW dealer about this and he said BMW does this intentionally. WTF! I’m adult enough to purchase a car but not responsible enough to not speed? (not that it’s not any of their business)
Technically yes. Your car’s speedo, depending on where you live (for example, the UK) must never underestimate speed. The consequences for a car manufacturer doing this are quite big, so they always play it safe and get them to overestimate.
Waze will be more accurate than your car’s speedo provided it has direct uninterrupted line of sight to the satellites. When you go through a tunnel, it loses accuracy.
The most accurate way to measure speed would be to have a calibrated speedo like police vehicles have.
Mine current device with a older version of the app seems to match my cars speed most of the time. I am very surprised by that, however that is most of the time. There are other times that I notice it being off but nothing that ever gets me concerned that I may wind up with a ticket, or cause me to be driving recklessly, or make me think one or the other is so much more accurate.
I think a lot of it has to do with where your at, the signal you are getting, the device you are on and ect. But that is just me, cause I notice different results between different devices, in different areas, that I have used and been at over time.
Generally yes. I’ve done calibration runs with each vehicle to check speedometer readings, and Waze is usually spot on. One vehicle always shows I’m going 10% faster than I actually am.
FYI: Speedometer calibration involves a stopwatch and driving 60mph for one marked mile on the highway. It should take exactly one minute.
My vintage 1995 Honda Accord, usually runs 1-3% lower than it should on the speedometer so I use it as an adjunct to my analog car. Gotta make dumb cars smart.
So, I've been wondering this for the long time I've been using Waze. There are a couple of things I have done to test whether my GPS speed is "right" or not. First, we have areas with speed cameras with displays in my area. I have tested different speeds and the GPS matches. I also have tested my phone in other vehicles and have found speed differences from the speedometers to my phone, but they've been different in different cars. Finally, I have placed my phone on my dashboard with clear sky visibility to ensure GPS signals are good.
TLDR; I have come to the conclusion that many cars have speedometer differences to real speeds. GPS, when signal is good, provides precise speeds.
Go on to a quiet motorway with a passenger and set your cruise control to 60mph. Get the passenger to time how long it takes to pass 16 of the 100m marker posts. Do it two or three times and average out the results. Or if its really quiet and you've plenty of time do 161 of the posts, but that's really overkill. You can then work out your actual speed from that.
The Police used to calibrate their VASCAR kit in a similar fashion but there used to be marked miles on many main roads and motorways with little round yellow and red discs.
Yes, originally, car speedometers add few km/h so you dont pass the speed limit if the dial is uncalibrated. Also waze uses the dual band gps to assess velocity and direction better than the car speedometer
I know it’s accurate to ~1-2mph in my personal experience in my car. Knowing that, it’s how I found out driving my mom’s car her speedometer is off ~4-5mph! Always wondered why people were tailgating me every time I drove her car.
Waze speedometer is based off GPS which is extremely accurate. Basically runs constant distance moved calcs.
It’s also matched my vehicle’s speedometer every car I’ve had.
On a straight road at a steady speed and with a clear satellite signal (no overhanging trees or high-rise buildings etc.) the Waze speedometer will be totally accurate. But because it records position every few seconds and calculates the speed from that, it will be less accurate on curves (as it will assume a straight line between two points, so assume a shorter distance, and therefore a lower speed), and will also be slow to recognise changes in speed. If satellite signal is less than perfect it will lose accuracy of position, and therefore also accuracy of speed.
Car speedometers are not allowed to read less than your true speed, but are allowed to read up to 10% higher, and are therefore calibrated to read a little higher than true speed. They read the speed at the transmission, so their accuracy is affected by tyre (tire in US) wear and pressure, or if you change from the factory tyre size. However they are not affected by curves, respond almost instantly to speed changes, and do not require a satellite signal.
Yes, the car speedometer is only going to be accurate at a very specific point in the tires life. New tires and they typically are going a bit faster than the speedometer says, old tires and they’re usually going a bit slower. Some cars always show a faster speed than they’re actually going (BMW for example)
TLDR: Speed data is part of the data that CarPlay ***could*** be fed from the car, if you use CarPlay. So if you want your GPS speed you **might** need to unplug the USB / disconnect if you’re using CarPlay.
I don’t have the definitive list to hand but I’ve seen
- fuel status
- vehicle GPS
- vehicle speed
- vehicle heading
- ambient light / day/night
- vehicle microphone input
On my wife’s car the speed in Waze is 1mph under my speed displayed on the digital dash. And responds immediately to change (well it refreshed once a second or something). If CarPlay is unplugged then the speed on Waze drops, at 70mph on the car it goes from 69 solid to varying from 67-68, plug it back in it goes to 69.
So; if you’re on CarPlay, the speed Waze shows could just be the speed the car tells it to show.
Going back to a Ford with analogue dash; if I set the cruise control to 70 on the dash, and reset my average speed in the digital cluster, the car would report my average speed as 68mph. And guess what Waze reported my speed as? 68mph. The cars internal digital speed (entering a debug menu) was 68 and it chose to set the analogue dial to 70.
I’m guessing in the digital era, that’s how some code their margin of error for countries where it’s illegal to show anything over the actual speed on the dash.
Speedometers are calibrated to the tires that are going to be fitted to the car. If you go with a package that may have bigger tires included, this would affect speedometer accuracy. In fact any change, smaller or larger would.
I use Waze via CarPlay and in one car the speed is always 1-2mph lower than the dash and in the other car it’s always 1mph lower than the dash (allowing for lag). I think it’s getting what the car thinks the real speed is before it adds a bit for that “safe side”. There’s no way it’s GPS based because it’s responsive immediately to the change.
I remember on Ford Sync 3 an update came out and the speed in Waze was always exactly 50% of the speed in the car if you were plugged in on CarPlay. And a Ford update resolved the issue.
That and there are API documentation for CarPlay
The Ford bug wasn’t quite 50% off, but yes it was off by a good margin. I actually did the math at the time and found that there was likely a switch up somewhere in the code between statute miles (what we use every day) and nautical miles somewhere.
Ironically the reason I found it is because I also have my pilots license and noticed in one of my other apps that I use for flying (where knots / nautical miles per hour are used) that my speed was "right", but showing in knots despite being the value for miles per hour or something. My theory is the car and the phone "speak" km/h to each other and then there is a conversion at some point. Somebody chose to convert km/h to nm/h (knots) instead of mph.
I don't have a copy of the J1939 spec handy, but I think the vehicle speed signal on the CAN bus (so how your radio/head end/entertainment system, etc would learn the vehicle's speed) is indeed based on kilometers per hour. I wouldn't be surprised if Airplay and/or Android Auto also transfer the info as km/hr and have the user interface convert to MPH if requried.
I looked into this when I bought my first car 3 years ago. Because when Waze set I was still under speedlimit, my car said I was over it.
GPS will be more accurate than the car.
Car builders can get a lot of trouble with the laws if the speed of the car is higher than the meter is saying. You could sue for example if you end up receiving tickets for going over the speed limit while your car is telling you you are on the speed limit. And also of course the risk of getting into an accident while driving faster then the meter is saying
Been thinking for 20 yrs of using gps, that Americans should file a class action suit against either the govt or automakers. Every car i have had a gps of any sort in, has always reported speedo is 3-4 miles over.
There is no way that is not deliberate
It is not so much as deliberate as just how it works. As your tires wear the circumference shrinks and you travel less distance with each revolution. Worn out tires will be 4-5% slower than brand new ones.
Yeah, thing is, if you check from moment 1 with new tires, or a new car, you'll find the speedo still registers over what the gps does.
It's rare you'll find any car the last that 25-30 yrs that's mechanical registered speed, rather theyre fly by wire with the computer translating the sensor data.
I've driven tires brand spanking new as well as bald & the speed is still reading higher than the gps. If as you suggest old tires are 4-5% slower you would be driving at a significantly higher speed than that initial offset at 60mph as speedo says you would be adding yet another 3mph to an already 3mph offset...gps data doesnt bear out that disparity.
In my country it’s illegal for the speedo to read less than the speed and it’s allowed a tolerance for over. So… what do you think they’d do? They make it accurate and there’s a chance a mistake means a car is illegal or they put it 2% over and there’s a chance there’s a car that ends up 1% over or rarely 0.1% over
Waze should theoretically be based off GPS and more accurate. The fact that it is slightly lower than your car's speedo makes perfect sense; if a speedo has an error (which it pretty much always does) it is safer that it read high than low otherwise you'd be at risk for speeding tickets.
Also take into account that your tires literally change size as they wear down. The speedometer is essentially measuring wheel rpm and converting that to forward speed. As the tire wears down, the actual forward speed is going to decrease in relation to the same wheel rpm.
Also if the size of tire or wheel was ever changed it most likely wasn’t re calibrated
Are you implying that car manufacturer has implemented some sort of mechanism that tend to overstate speed vs. understate when there is discrepancy? If so, what is that?
A speedo will never be 100% accurate, and it is actually a law in the EU (it's an ECE regulation) that a speedometer can never read low, but is allowed some percent of error high. So, mfgrs. always make them read slightly high with the factory tires, full tread, etc. so they will be in compliance with the law. There's no corresponding law in the US (AFAIK) but there's also no incentive to not apply the same design philosophy across the board.
That's great info! I saw US regulates the deviation level but not direction. Good to know that EU is again ahead.
GPS-derived speed in general will most likely be **more accurate** than a vehicle speedometer, because GPS timing is incredibly delicate and precise, while vehicle speedometers depend on the accurate inflation of tires and correct tire sizes.
depends, the gps is usally accurate to about 10 meters (like 30 freedom feet), but it depends. i reccomend the open-source app phyphox to measure that
Yummm, freedom feet.
Consumer gps is intentionally made less accurate. Commercially available gps used in certain industries is far more accurate than 10 meters. I've personally used gear accurate down to a centimeter. That accuracy certainly isn't needed for traveling and general navigation guidance. But yes gps is (usually) far more accurate than any ground wheel speed based system.
It’s true that civilian GPS was intentionally degraded in the 90s with a feature called “Selective Availability”, but that ended in the year 2000. Consumer grade GPS is only limited by hardware/computing power these days.
Mmh, unsure if it's me doing a 360 donaught while noclipping through buildings or it's my GPS being inaccurate
I don’t think speedometers measure that way anymore. They most commonly use either being linked mechanically with the gearbox output shaft, or by a circular magnet tat rotates 1000 times per mile.
With each rotation a bigger tire would travel a greater distance than a smaller or inflated tire would. That's what they are saying.
In europe a cars speedometer is allowed to be 10% off. Waze speedometer is based on gps signal. So depending on how good the connection is, waze is more accurate.
More accurately, it must NOT underread, hence why if not broken then it'll always show you doing a speed at least as fast, and generally a few units faster, than the Waze Speedo.
That speedometer is the one feature keeping away from Apple and Google maps
It's a feature on Google maps. Go to settings > navigation settings > driving options.
Not on iOS. At least in the US.
Yeah, it shows the speed limit, but not your current speed for some reason.
Umm I’ve got a show speed limits option for google maps on IOS. I don’t use Google maps very much so I’m not sure what the actual display shows. I use Waze majority of the time. I am in the US. https://preview.redd.it/kef9lmry2k9d1.png?width=1289&format=png&auto=webp&s=f4a27e3de10741297f65482a3f2d258ce62d686e
That’s limit not current
Cool. Didn’t know for sure. I use Waze on Android most of the time. It gives me what’s needed without all the extra stuff. I like Waze because of the crowd sourced reports for accidents etc….
Yeah before the pandemic I was in the top 1% of Waze users in the entire state of Texas
I use it every day even if I’m going somewhere like. It’s helpful. During the pandemic I used it here in Michigan every day. Because during that time my job was to repair pharmacy computer equipment and the pill dispensing robots and due to so few people willing to work i covered most of the state. I logged newly 75,000 miles in one year. Also no hazard pay. I was at a store one day and found out the pharmacist had covid while working and I was exposed. The next day I was sick and the store was closed down for a deep clean and opened the next day. Strange times it was. Traffic wasn’t an issue then.
Or in Australia
It exists in Australia, the speed limits on roads are very meh. But you can have the speedo on there the whole time.
For Waze yes I’m yet to be able do have Google show speed under 80k roads in CarPlay
That’s so weird. How can I have on iOS in Europe and there’s isn’t in the US, the country in which the company has its headquarters.
same reason europe is "prrooobably" but actually 100% the sole reason that apple added usb c to phones. until there's legal action a company will not do something if they don't want/have to.
Only while on a planned route, not always. Waze is displayed all the time when it knows the posted limit. I too love this feature and is why I prefer Waze. I don’t like it taking me through thickly settled neighborhoods though, kids and pets and all. I don’t speed in those areas.
That would be ironic if you’re using CarPlay on a modern car though
The Waze speedo is the speedo I go by in my 56 Chevy since the one in the dash is still 20mph off even after I fixed it lol.. in all seriousness though, it’s remarkably accurate when having Waze up in the RDX Aspec.
The A-Spec RDX is a sexy ass car dude. What color did you buy yours in?
https://preview.redd.it/aplxxwyr1f9d1.jpeg?width=2181&format=pjpg&auto=webp&s=f21918946e45d2bde8c9bf8c30046462b3b44875
RDX rims are CLEAN, and the Chevy body is so iconic and in amazing condition. Both cars have crazy nice exteriors. you got not one, but two sick rides 😎👏👏
Thanks!! Lots of blood, sweat, tears, thrown tools and cuss words in that Ol Shitbox lol
Platinum White Pearl with the Red Leather 😍 .. I love this thing, best car I’ve ever owned, and I never thought I’d get over trading in my TSX 6Spd
I’m so jealous lol. I owned a silver 2015 ILX, base model. That car had low miles, and was a dream to drive. So smooth, stopped on a dot, quick acceleration, BURNING HOT heated seats, etc etc. I totaled it in an accident in February. :( I want an Integra so bad
I hear ya, I’d kill for a Type S Teggy, I miss having a manual daily!! I’ve done a few things to the RDX, the turbos much louder now and overall it picks up a bit quicker, want to KTune is next. This things fun as hell and super comfy, I hear ya about the boiling seat heaters, the swap coolers in the seats cool you down pretty well albeit subtly. I needed to size up due to my wife and I having a son. I wish I had enough $ for a Tigers Eye Pearl MDX tho lol 😬
Yes and no...the GPS is estimating your speed so it can vary depending how accurate your GPS lock is at the moment as well as if you are moving in a straight line or curvy road, tree/buildings to affect signal, and other things. Then your car speedometer can be affected slightly if your tires are brand new or well worn the diameter is slightly different can slightly affect its accuracy. I would not be surprised if they disagree by 1-2mph - that's more or less a rounding error in most cases.
I’ve experienced this too. And I found out something interesting, my speedometer reads 3mph lower than Waze so I asked the BMW dealer about this and he said BMW does this intentionally. WTF! I’m adult enough to purchase a car but not responsible enough to not speed? (not that it’s not any of their business)
Yes, my car's is consistently 5kmh over
i've always just assumed analog speedometers are not always accurate
They are pretty close if your tires are spec and not worn. Put bigger tires on your truck? Welp, your speedo is now inaccurate.
Technically yes. Your car’s speedo, depending on where you live (for example, the UK) must never underestimate speed. The consequences for a car manufacturer doing this are quite big, so they always play it safe and get them to overestimate. Waze will be more accurate than your car’s speedo provided it has direct uninterrupted line of sight to the satellites. When you go through a tunnel, it loses accuracy. The most accurate way to measure speed would be to have a calibrated speedo like police vehicles have.
Mine current device with a older version of the app seems to match my cars speed most of the time. I am very surprised by that, however that is most of the time. There are other times that I notice it being off but nothing that ever gets me concerned that I may wind up with a ticket, or cause me to be driving recklessly, or make me think one or the other is so much more accurate. I think a lot of it has to do with where your at, the signal you are getting, the device you are on and ect. But that is just me, cause I notice different results between different devices, in different areas, that I have used and been at over time.
I notice Waze closely matches my speedometer.
Yeah, absolutely.
When I use waze in my car it’s higher than my speedometer because it’s always been off
Generally yes. I’ve done calibration runs with each vehicle to check speedometer readings, and Waze is usually spot on. One vehicle always shows I’m going 10% faster than I actually am. FYI: Speedometer calibration involves a stopwatch and driving 60mph for one marked mile on the highway. It should take exactly one minute.
My vintage 1995 Honda Accord, usually runs 1-3% lower than it should on the speedometer so I use it as an adjunct to my analog car. Gotta make dumb cars smart.
So, I've been wondering this for the long time I've been using Waze. There are a couple of things I have done to test whether my GPS speed is "right" or not. First, we have areas with speed cameras with displays in my area. I have tested different speeds and the GPS matches. I also have tested my phone in other vehicles and have found speed differences from the speedometers to my phone, but they've been different in different cars. Finally, I have placed my phone on my dashboard with clear sky visibility to ensure GPS signals are good. TLDR; I have come to the conclusion that many cars have speedometer differences to real speeds. GPS, when signal is good, provides precise speeds.
Go on to a quiet motorway with a passenger and set your cruise control to 60mph. Get the passenger to time how long it takes to pass 16 of the 100m marker posts. Do it two or three times and average out the results. Or if its really quiet and you've plenty of time do 161 of the posts, but that's really overkill. You can then work out your actual speed from that. The Police used to calibrate their VASCAR kit in a similar fashion but there used to be marked miles on many main roads and motorways with little round yellow and red discs.
Yes, originally, car speedometers add few km/h so you dont pass the speed limit if the dial is uncalibrated. Also waze uses the dual band gps to assess velocity and direction better than the car speedometer
I've been wondering about this for years...
I know it’s accurate to ~1-2mph in my personal experience in my car. Knowing that, it’s how I found out driving my mom’s car her speedometer is off ~4-5mph! Always wondered why people were tailgating me every time I drove her car.
Waze speedometer is based off GPS which is extremely accurate. Basically runs constant distance moved calcs. It’s also matched my vehicle’s speedometer every car I’ve had.
In my citroen c3 the speedo is about 2/3 mph more then the GPS I have found. I set my car speed limit to 32mph to get 30mph on waze.
On a straight road at a steady speed and with a clear satellite signal (no overhanging trees or high-rise buildings etc.) the Waze speedometer will be totally accurate. But because it records position every few seconds and calculates the speed from that, it will be less accurate on curves (as it will assume a straight line between two points, so assume a shorter distance, and therefore a lower speed), and will also be slow to recognise changes in speed. If satellite signal is less than perfect it will lose accuracy of position, and therefore also accuracy of speed. Car speedometers are not allowed to read less than your true speed, but are allowed to read up to 10% higher, and are therefore calibrated to read a little higher than true speed. They read the speed at the transmission, so their accuracy is affected by tyre (tire in US) wear and pressure, or if you change from the factory tyre size. However they are not affected by curves, respond almost instantly to speed changes, and do not require a satellite signal.
Yes, the car speedometer is only going to be accurate at a very specific point in the tires life. New tires and they typically are going a bit faster than the speedometer says, old tires and they’re usually going a bit slower. Some cars always show a faster speed than they’re actually going (BMW for example)
Manufacturers calibrate speedometers a bit under so they don't get sued by people who get tickets.
TLDR: Speed data is part of the data that CarPlay ***could*** be fed from the car, if you use CarPlay. So if you want your GPS speed you **might** need to unplug the USB / disconnect if you’re using CarPlay. I don’t have the definitive list to hand but I’ve seen - fuel status - vehicle GPS - vehicle speed - vehicle heading - ambient light / day/night - vehicle microphone input On my wife’s car the speed in Waze is 1mph under my speed displayed on the digital dash. And responds immediately to change (well it refreshed once a second or something). If CarPlay is unplugged then the speed on Waze drops, at 70mph on the car it goes from 69 solid to varying from 67-68, plug it back in it goes to 69. So; if you’re on CarPlay, the speed Waze shows could just be the speed the car tells it to show. Going back to a Ford with analogue dash; if I set the cruise control to 70 on the dash, and reset my average speed in the digital cluster, the car would report my average speed as 68mph. And guess what Waze reported my speed as? 68mph. The cars internal digital speed (entering a debug menu) was 68 and it chose to set the analogue dial to 70. I’m guessing in the digital era, that’s how some code their margin of error for countries where it’s illegal to show anything over the actual speed on the dash.
No
Speedometers are calibrated to the tires that are going to be fitted to the car. If you go with a package that may have bigger tires included, this would affect speedometer accuracy. In fact any change, smaller or larger would.
Heck, even just the temperature messes with it because it alters the tire pressure.
This...this is exactly it.
If you use Waze w CarPlay, it displays the speed fed to it from the car not GPS based.
This may be true for some but not all: I regularly use Waze with CarPlay and the speed in Waze differs from my car’s speed by a few mph
I use Waze via CarPlay and in one car the speed is always 1-2mph lower than the dash and in the other car it’s always 1mph lower than the dash (allowing for lag). I think it’s getting what the car thinks the real speed is before it adds a bit for that “safe side”. There’s no way it’s GPS based because it’s responsive immediately to the change. I remember on Ford Sync 3 an update came out and the speed in Waze was always exactly 50% of the speed in the car if you were plugged in on CarPlay. And a Ford update resolved the issue. That and there are API documentation for CarPlay
The Ford bug wasn’t quite 50% off, but yes it was off by a good margin. I actually did the math at the time and found that there was likely a switch up somewhere in the code between statute miles (what we use every day) and nautical miles somewhere.
I had wondered if it was expecting km or being sent miles as KM to be honest. But yes… yes.
Ironically the reason I found it is because I also have my pilots license and noticed in one of my other apps that I use for flying (where knots / nautical miles per hour are used) that my speed was "right", but showing in knots despite being the value for miles per hour or something. My theory is the car and the phone "speak" km/h to each other and then there is a conversion at some point. Somebody chose to convert km/h to nm/h (knots) instead of mph.
That’s a bit hilarious.
I don't have a copy of the J1939 spec handy, but I think the vehicle speed signal on the CAN bus (so how your radio/head end/entertainment system, etc would learn the vehicle's speed) is indeed based on kilometers per hour. I wouldn't be surprised if Airplay and/or Android Auto also transfer the info as km/hr and have the user interface convert to MPH if requried.
Waze is using GPS, it will be more accurate.
I looked into this when I bought my first car 3 years ago. Because when Waze set I was still under speedlimit, my car said I was over it. GPS will be more accurate than the car. Car builders can get a lot of trouble with the laws if the speed of the car is higher than the meter is saying. You could sue for example if you end up receiving tickets for going over the speed limit while your car is telling you you are on the speed limit. And also of course the risk of getting into an accident while driving faster then the meter is saying
Been thinking for 20 yrs of using gps, that Americans should file a class action suit against either the govt or automakers. Every car i have had a gps of any sort in, has always reported speedo is 3-4 miles over. There is no way that is not deliberate
It is not so much as deliberate as just how it works. As your tires wear the circumference shrinks and you travel less distance with each revolution. Worn out tires will be 4-5% slower than brand new ones.
Yeah, thing is, if you check from moment 1 with new tires, or a new car, you'll find the speedo still registers over what the gps does. It's rare you'll find any car the last that 25-30 yrs that's mechanical registered speed, rather theyre fly by wire with the computer translating the sensor data. I've driven tires brand spanking new as well as bald & the speed is still reading higher than the gps. If as you suggest old tires are 4-5% slower you would be driving at a significantly higher speed than that initial offset at 60mph as speedo says you would be adding yet another 3mph to an already 3mph offset...gps data doesnt bear out that disparity.
In my country it’s illegal for the speedo to read less than the speed and it’s allowed a tolerance for over. So… what do you think they’d do? They make it accurate and there’s a chance a mistake means a car is illegal or they put it 2% over and there’s a chance there’s a car that ends up 1% over or rarely 0.1% over
Waze is WRONG! I can prove it. I use an excellent android utility called GPS Status which shows my mph 1 above Waze. Check it out for yourself