Using Cell phone GPS System as Speedometer. Dangerous?

M

McCrazieGoalz

Expert Member
Joined
May 6, 2010
Messages
1,858
Reaction score
0
Location
right here
Recently, I bought a Nokia Lumia and started using it pretty much for anything.

One of the things that I like about it is the Maps and navigation (Nokia Drive).

So, I downloaded my maps and navigation is true offline navigation (see here).

The really cool thing about Nokia drive is that it acts as a speed monitor for you. It shows you which speed you are travelling at and what the speed limit in the place you are driving is. Further, it beeps when you exceed the speed limit. With that said, I noticed that the speed on my car's speedometer was far lower than what my Lumia navigation app was saying. To top this off, earlier this month, I was driving a different car and I noticed that the 120km/hr in this car was much faster than the 120km/hr in my car and that this other car's 120km/hr almost always matched the Lumia's GPS's.

On coming back to my car, I have been doing some serious tests. I have now realised that my 140km/hr (speedometer) is actually 125km/hr. So, I've now started using Nokia Drive as my speedometer. So, I now basically travel at 140km/hr using my car's speedometer.

Is this dangerous?

How accurate are GPS's as far as measuring the speed you are traveling at? I've recently downloaded an app called Dashboard PDA (it should also be available on iOS and Android), which gives you the option of displaying your height above sea level, your speed, the time or the direction in which you are traveling. The speed also shown by this app also indicated that my car's speedometer is about 10 to 15km/hr slower than what it would be measuring.

Is it safe to use a GPS as a speedometer?

Its only been a couple of days since I started doing this so perhaps the fines are still in the post or are still being written.
 
Last edited:
McCrazieGoalz said:
On coming back to my car, I have been doing some serious tests. I have now realised that my 140km/hr (speedometer) is actually 125km/hr. So, I've now started using Nokia Drive as my speedometer. So, I now basically travel at 140km/hr using my car's speedometer.
Click to expand...

Speedometers are required to be accurate on 60km/h.
You will notice that when car tests are done (taking for example the Car magazine) that they mention % over or under at certain speeds.
You would also have noticed that there is a leniency in speed traps, so a 100km/h speedtrap will only catch you from say 110km/h, this is to give you some leeway with regards to the inaccuracies of speedos.
 
The_Unnamed said:
My Garmin navigation on my Galaxy Note 2 is offline. :confused: Unless there is something i am missing?

That is all i have to add.
Click to expand...

Alright. I'll have to give you that. And I'll have to correct my post. But, you do have to pay for the Garmin app do you not. How much by the way? just out of interest. I hope not too much.
 
Last edited:
Remember that your gps uses sats for speed as well. It constantly calculates an average speed between two plotted points. It's not more accurate than your car's speedo.
 
McCrazieGoalz said:
Recently, I bought a Nokia Lumia and started using it pretty much for anything.

One of the things that I like about it is the Maps and navigation (Nokia Drive).

So, I downloaded my maps and navigation is true offline navigation (see here).

The really cool thing about Nokia drive is that it acts as a speed monitor for you. It shows you which speed you are travelling at and what the speed limit in the place you are driving is. Further, it beeps when you exceed the speed limit. With that said, I noticed that the speed on my car's speedometer was far lower than what my Lumia navigation app was saying. To top this off, earlier this month, I was driving a different car and I noticed that the 120km/hr in this car was much faster than the 120km/hr in my car and that this other car's 120km/hr almost always matched the Lumia's GPS's.

On coming back to my car, I have been doing some serious tests. I have now realised that my 140km/hr (speedometer) is actually 125km/hr. So, I've now started using Nokia Drive as my speedometer. So, I now basically travel at 140km/hr using my car's speedometer.

Is this dangerous?

How accurate are GPS's as far as measuring the speed you are traveling at? I've recently downloaded an app called Dashboard PDA (it should also be available on iOS and Android), which gives you the option of displaying your height above sea level, your speed, the time or the direction in which you are traveling. The speed also shown by this app also indicated that my car's speedometer is about 10 to 15km/hr slower than what it would be measuring.

Is it safe to use a GPS as a speedometer?

Its only been a couple of days since I started doing this so perhaps the fines are still in the post or are still being written.
Click to expand...

What does the download map for offline functions button do on Google maps? :confused:
 
ghoti said:
What does the download map for offline functions button do on Google maps? :confused:
Click to expand...

With Google Maps offline basically means you can look at the maps, turn the map around and drag to see the other areas that you downloaded. Its your fingers (not figures - corrected) that do the navigating on the maps basically and not the maps telling you how to get from point A to point B.

There is no navigation on Google Maps offline.
 
Last edited:
McCrazieGoalz said:
With Google Maps offline basically means you can look at the maps, turn the map around and drag to see the other areas that you downloaded. Its your figures that do the navigating on the maps basically and not the maps telling you how to get from point A to point B.

There is no navigation on Google Maps offline.
Click to expand...

Okay, cause the navigation did work with the map, but perhaps it was just a glitch. Ive downloaded the entire eastern cape.
 
froot said:
Speedometers are required to be accurate on 60km/h.
You will notice that when car tests are done (taking for example the Car magazine) that they mention % over or under at certain speeds.
You would also have noticed that there is a leniency in speed traps, so a 100km/h speedtrap will only catch you from say 110km/h, this is to give you some leeway with regards to the inaccuracies of speedos.
Click to expand...

It's actually from 111km/h in a 100km/h zone.
 
ghoti said:
Okay, cause the navigation did work with the map, but perhaps it was just a glitch. Ive downloaded the entire eastern cape.
Click to expand...

For navigation, Google maps always looks for an Internet connection. Try setting your phone to Flight Mode and then try navigating and see what happens. It will not get directions for you. It will not navigate for you. It will make you wait - until it finds an Internet connection.

Wondering where your data goes? There's your answer.

Don't be fooled. Google doesn't tell you. Google Offline is not true offline.
 
visrot said:
Remember that your gps uses sats for speed as well. It constantly calculates an average speed between two plotted points. It's not more accurate than your car's speedo.
Click to expand...

But, can this calculation be trusted since it was closer to the other car's reading and is constantly lower than my car's speedometer by 10 to 15km/hr meaning that my car may be giving me the illusion that I am travelling much faster than I really am.

Which should I rather trust?
 
GPS is more accurate than your car's speedo.
Most car speedos overread by up to 10%.
 
froot said:
Speedometers are required to be accurate on 60km/h.
Click to expand...
Not quite true. The accuracay of car speedometers must adhere to SANS 1441:2006, SOUTH AFRICAN NATIONAL STANDARD, Speedometer equipment on motor vehicles.

Here is what this standard has to say on the accuracy:
SANS 1441:2006
Edition 2

3 Requirements
NOTE The requirements of this standard should not apply to those vehicles fitted with a tachograph or speedrecording
equipment that has a visual speed-indicator incorporated that complies with 3.5.
3.1 Vehicles that are submitted for testing in accordance with clause 4 shall not differ with regards
to
a) tyres normally fitted,
b) overall transmission ratio including reduction drive, if fitted (number of revolutions at the
speedometer input per revolution of the axle driving the speedometer equipment when vehicle is
travelling in a straight line), or
c) type of speedometer equipment defined by the tolerance of the measuring mechanism of the
speedometer, the instrument constant and the range of indicated speeds.
3.2 The speedometer display shall be situated in the driver's direct field of vision and shall be
clearly legible both by day and by night. The range of speeds indicated shall include the maximum
speed given by the manufacturer for the type of vehicle.
3.3 Where the speedometer has a scale, as distinct from a digital display, it shall be clearly legible.
3.4 The graduations shall be of 1 km/h, 2 km/h, 5 km/h or 10 km/h. The values of the speed, as
multiples of 20 km/h, shall be indicated on a dial.
3.5 The speed indicated shall never be less than the true speed. At the speeds specified for the
test in 4.7, and between these speeds, there shall be the following relationship between the speed
indicated on the dial of the speedometer (V1) and the true speed (V2):
0 Smaller or equal V1 – V2 Smaller or equal V2/10 + 4 km/h.

4.7 Test the speedometer of the vehicle against the accurate test instrumentation at 40 km/h,
80 km/h and 120 km/h, or 80 % of the maximum speed specified by the manufacturer, if this is less
than 150 km/h.
 
McCrazieGoalz said:
For navigation, Google maps always looks for an Internet connection. Try setting your phone to Flight Mode and then try navigating and see what happens. It will not get directions for you. It will not navigate for you. It will make you wait - until it finds an Internet connection.

Wondering where your data goes? There's your answer.

Don't be fooled. Google doesn't tell you. Google Offline is not true offline.
Click to expand...

The data doesnt bother me. I have tons of it. Just sometimes the lack of access to data bothers me.
 
geezer said:
Not quite true. The accuracay of car speedometers must adhere to SANS 1441:2006, SOUTH AFRICAN NATIONAL STANDARD, Speedometer equipment on motor vehicles.

Here is what this standard has to say on the accuracy:
SANS 1441:2006
Edition 2

3 Requirements
NOTE The requirements of this standard should not apply to those vehicles fitted with a tachograph or speedrecording
equipment that has a visual speed-indicator incorporated that complies with 3.5.
3.1 Vehicles that are submitted for testing in accordance with clause 4 shall not differ with regards
to
a) tyres normally fitted,
b) overall transmission ratio including reduction drive, if fitted (number of revolutions at the
speedometer input per revolution of the axle driving the speedometer equipment when vehicle is
travelling in a straight line), or
c) type of speedometer equipment defined by the tolerance of the measuring mechanism of the
speedometer, the instrument constant and the range of indicated speeds.
3.2 The speedometer display shall be situated in the driver's direct field of vision and shall be
clearly legible both by day and by night. The range of speeds indicated shall include the maximum
speed given by the manufacturer for the type of vehicle.
3.3 Where the speedometer has a scale, as distinct from a digital display, it shall be clearly legible.
3.4 The graduations shall be of 1 km/h, 2 km/h, 5 km/h or 10 km/h. The values of the speed, as
multiples of 20 km/h, shall be indicated on a dial.
3.5 The speed indicated shall never be less than the true speed. At the speeds specified for the
test in 4.7, and between these speeds, there shall be the following relationship between the speed
indicated on the dial of the speedometer (V1) and the true speed (V2):
0 Smaller or equal V1 – V2 Smaller or equal V2/10 + 4 km/h.

4.7 Test the speedometer of the vehicle against the accurate test instrumentation at 40 km/h,
80 km/h and 120 km/h, or 80 % of the maximum speed specified by the manufacturer, if this is less
than 150 km/h.
Click to expand...

I left out perhaps a key piece of information.

My car has mag wheels which I believe are larger than the normal size of rims for the car. I am sure that this could be the contributing factor. Perhaps they (the dealership) then calibrated it so that the speedomenter reading is more than the original calibration so as to make it not give a reading that is lower than the actual speed. In so doing they then perhaps then over inflated the speedometer reading so that it is much more than the real speed.

But, where or how can I get an accurate reading for my car's speed. Any suggestions?
 
McCrazieGoalz said:
I left out perhaps a key piece of information.

My car has mag wheels which I believe are larger than the normal size of rims for the car. I am sure that this could be the contributing factor. Perhaps they (the dealership) then calibrated it so that the speedomenter reading is more than the original calibration so as to make it not give a reading that is lower than the actual speed. In so doing they then perhaps then over inflated the speedometer reading so that it is much more than the real speed.
Click to expand...

This does make a difference, given that the rolling circumference of the wheel has now changed. Dealerships won't calibrate your speedo, this is done at the factory. So a change in wheel size normally affects your speedo reading.

But, where or how can I get an accurate reading for my car's speed. Any suggestions?
Click to expand...

GPS is the most accurate you can get commercially, unless you want something like this, which is probably overkill.
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X