My RX300 & RX450h are optimistic by 2 mph, at all speeds. Meaning when the speedometer reads 75, I'm really going 73.
GPS Speed vs. Speedometer
- Thread starter Roger
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Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
Both of my Toyotas read 2 mph fast at most all speeds above about 10 mph. I understand this is designed-in. The speed sensor is reading the correct speed, and the odometer is correct, but the speedometer is programmed to add 2 mph to the signal and display that.
Both of our Hondas are dead spot-on. Both of our Chryslers were also bang-on. Every Ford I've driven has been bang-on. GMs and Toyotas seem to often be optimistic.
Both of our Hondas are dead spot-on. Both of our Chryslers were also bang-on. Every Ford I've driven has been bang-on. GMs and Toyotas seem to often be optimistic.
A GPS should be nearly 100% accurate, at least at steady speed with good signal level. They calculate speed by calculating change of position over time. GPS time has to be very accurate, and obviously position is going to be accurate to within a few meters.
So probably the speedometer is off.
So probably the speedometer is off.
Originally Posted By: Quattro Pete
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
Well, it's stupid. Ironically our 30 year old BMW is dead on.
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
Well, it's stupid. Ironically our 30 year old BMW is dead on.
Originally Posted By: Roger
I've noticed when using my TomTom that the speed I'm traveling at is not the same speed as my speedometer on the Camry (or my Sienna van for that matter too). The GPS is always higher. For example, when the car says I'm going 70 mph, the GPS reads 74-75. Lately I went past a radar gun in a construction zone and it read low too, i.e.: my speed was 42 when the speedometer was set at 45. When I asked my dealer if they could check/adjust the speedometer, I was told no. They are sealed.
How accurate is a GPS speed reading? I'm beginning to suspect it is correct. Kinda curious before I go past a trooper.
I have two TomTom GPS units. They're both identical except for the model # and a pictigraph.
Both my wifes('01 RX-300) and my car('04 Altima 2.5) read(depending on the speed traveled) about 2, 2.5, 3 mph slower on the GPS units than on the vehicles speedometer. The RX-300(w/o the OE GPS) also has an digital readout in MPH or Km/h in the Information Screen, which also reflects the TomTom.
Once a year, our local Police Dept. sets up those large digital Radar MPH units on certain roads. These are not speed traps but, they are accurate/calibrated to let driver know of their speed in certain areas(child or chalanged/disabeled person areas).
When traveling down these roads, I'll set the cruise control at, Oh lets say, 40 mph. In all of our cars, the Police(lets call'em "RADAR UNITS"). readout is ~37-38 mph except for my daughters Mazda3, where it's right on the money.
This Mazda3 is right on the money, comparing here speedometer reading with those Police Radar Units on the street or with either of our two TomTom GPS Units. It's the only vehicle in our family that is right on the money regardless of the unit we'er using to make a comparison.
Even in past years with other vehicles, the speedometer readings are on one side or the other but, not on the money as in this Mazda3. Most cars that I have owned read higher on the cars speedometer(a good thing I guess!)
I've noticed when using my TomTom that the speed I'm traveling at is not the same speed as my speedometer on the Camry (or my Sienna van for that matter too). The GPS is always higher. For example, when the car says I'm going 70 mph, the GPS reads 74-75. Lately I went past a radar gun in a construction zone and it read low too, i.e.: my speed was 42 when the speedometer was set at 45. When I asked my dealer if they could check/adjust the speedometer, I was told no. They are sealed.
How accurate is a GPS speed reading? I'm beginning to suspect it is correct. Kinda curious before I go past a trooper.
I have two TomTom GPS units. They're both identical except for the model # and a pictigraph.
Both my wifes('01 RX-300) and my car('04 Altima 2.5) read(depending on the speed traveled) about 2, 2.5, 3 mph slower on the GPS units than on the vehicles speedometer. The RX-300(w/o the OE GPS) also has an digital readout in MPH or Km/h in the Information Screen, which also reflects the TomTom.
Once a year, our local Police Dept. sets up those large digital Radar MPH units on certain roads. These are not speed traps but, they are accurate/calibrated to let driver know of their speed in certain areas(child or chalanged/disabeled person areas).
When traveling down these roads, I'll set the cruise control at, Oh lets say, 40 mph. In all of our cars, the Police(lets call'em "RADAR UNITS"). readout is ~37-38 mph except for my daughters Mazda3, where it's right on the money.
This Mazda3 is right on the money, comparing here speedometer reading with those Police Radar Units on the street or with either of our two TomTom GPS Units. It's the only vehicle in our family that is right on the money regardless of the unit we'er using to make a comparison.
Even in past years with other vehicles, the speedometer readings are on one side or the other but, not on the money as in this Mazda3. Most cars that I have owned read higher on the cars speedometer(a good thing I guess!)
I experience this in my RX. According to my tomtom,my speedo is reading 1 to 1.5 mph faster than i`m going.
In the Neon the dash speedo is about 7% fast with stock sized tires. The ECU's speed reading is about 3% fast(read from my scangauge)
With my snow tires the speedo is about 12% fast so I calibrated the scangauge speed reading to be about 1% fast.
The Tracker dash speedo is about 1% fast and matches the ECU's speed reading pretty much exactly.
With my snow tires the speedo is about 12% fast so I calibrated the scangauge speed reading to be about 1% fast.
The Tracker dash speedo is about 1% fast and matches the ECU's speed reading pretty much exactly.
Odd tire are a good candidate for this variance. 4-5 MPH off is a lot - it would annoy me
BTW, your speedometer and odometer run off the same source, but may be off in different directions.
BTW, your speedometer and odometer run off the same source, but may be off in different directions.
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Originally Posted By: Quattro Pete
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
In my VW when traveling at what the speedometer says is 120km/hr the GPS is reading 113km/hr.
In my Dodge Nitro they are a match.
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
In my VW when traveling at what the speedometer says is 120km/hr the GPS is reading 113km/hr.
In my Dodge Nitro they are a match.
How hard is it to recalibrate a speedo yourself?
Originally Posted By: cadfaeltex
How hard is it to recalibrate a speedo yourself?
I dont think you can.
How hard is it to recalibrate a speedo yourself?
I dont think you can.
Originally Posted By: cadfaeltex
How hard is it to recalibrate a speedo yourself?
Google your car's make and model. I was surprised that some have facilities for it. But, for your general AAA speedometer calibration test all they do is put it on a rolling road and give you a printout of your speedometer reading vs. actual road speed.
The easiest way is to buy a GPS and use it.
The Garmin model I have has a mode made more for aviation.
The screen becomes a black background with white lettering, and has a big speedometer/compass in the upper-middle of the screen.
How hard is it to recalibrate a speedo yourself?
Google your car's make and model. I was surprised that some have facilities for it. But, for your general AAA speedometer calibration test all they do is put it on a rolling road and give you a printout of your speedometer reading vs. actual road speed.
The easiest way is to buy a GPS and use it.
The Garmin model I have has a mode made more for aviation.
The screen becomes a black background with white lettering, and has a big speedometer/compass in the upper-middle of the screen.
Since I know from those road side things, and my gps that my speedo is reading slightly faster than what I`m actually going.(which is probably a good thing). I know how to adjust accordingly.
Originally Posted By: cchase
Originally Posted By: Quattro Pete
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
Well, it's stupid. Ironically our 30 year old BMW is dead on.
Now come to think of it, my '01 A4 was spot on as well.
Originally Posted By: Quattro Pete
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
Well, it's stupid. Ironically our 30 year old BMW is dead on.
Now come to think of it, my '01 A4 was spot on as well.
Originally Posted By: cadfaeltex
How hard is it to recalibrate a speedo yourself?
Depends on the vehicle. On older ones, it was a matter of gears and plenty of shops could do it.
How hard is it to recalibrate a speedo yourself?
Depends on the vehicle. On older ones, it was a matter of gears and plenty of shops could do it.
The trick there is whether a gear exists to change the rate correctly.
Originally Posted By: Scum_Frog
Originally Posted By: Quattro Pete
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
In my VW when traveling at what the speedometer says is 120km/hr the GPS is reading 113km/hr.
Same for my 2012 TDI. When at 105km/h on the speedo, the GPS reads 100km/h. At 120km/h on speedo , GPS reads 114km/h.
On my CTS, the Speedo and the GPS both read the same.
Originally Posted By: Quattro Pete
Originally Posted By: cchase
BMW specs call for 10% +/- 5 mph accuracy or some such nonsense.
That's not a BMW spec. That's a European Union directive which BMW as well as all other European manufacturers have to follow.
My e39 is off by about 3-4 mph.
In my VW when traveling at what the speedometer says is 120km/hr the GPS is reading 113km/hr.
Same for my 2012 TDI. When at 105km/h on the speedo, the GPS reads 100km/h. At 120km/h on speedo , GPS reads 114km/h.
On my CTS, the Speedo and the GPS both read the same.
Originally Posted By: lexus114
I experience this in my RX. According to my tomtom,my speedo is reading 1 to 1.5 mph faster than i`m going.
Exactly! What I have also noticed with our (non-OE GPS) '01 RX is...
If I reset to zero, the MPH in the dash screen and allow it to read my constant speed, this speed reading on the dash matches the tomtom GPS within 1or2 10ths/MPH although the speedometer will always read a higher MPH.
What is not accurate in this dash screen(and has nothing to do with the SPEED vs GPS) is, the AVE MPG compared to my calculated MPG. The Dash Reading is always higher than my calc reading.
I experience this in my RX. According to my tomtom,my speedo is reading 1 to 1.5 mph faster than i`m going.
Exactly! What I have also noticed with our (non-OE GPS) '01 RX is...
If I reset to zero, the MPH in the dash screen and allow it to read my constant speed, this speed reading on the dash matches the tomtom GPS within 1or2 10ths/MPH although the speedometer will always read a higher MPH.
What is not accurate in this dash screen(and has nothing to do with the SPEED vs GPS) is, the AVE MPG compared to my calculated MPG. The Dash Reading is always higher than my calc reading.
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