Hi all,

 

I downloaded "SpeedView" on my phone today, and checked the speedometer vs. GPS readings.

When the speedometer reads 80km/h, the GPS reads 70km/h. That is an error of 14%. Thus, fuel consumption would actually be worse than I thought.

Also, the tripmeter would display 14% longer driving distance than the car actually has traveled. Mine reads now approx 30 000km, but in reality it has traveled "only" 26 250km.

 

However, at 50km/h on the speedometer, the GPS reads 41 - which is 22% error... Is this normal?

 

Vidar

Not sure I understand what you mean, if it helps the PID GPS speed will usually be out by a few KMH/MPH but not by 10KMH, perhaps 2 or 3 sometimes 5, best bet is to look at the speedo

The speedo will always be out by a small percentage but not quite what you have but do you really trust that app?

I wouldn't to be honest.

Sent from my iPhone using Tapatalk

Which tyres you have "Citigo2032"? Smaller than stock perhaps for winter? I have not calculated carefully, but less than 10% here I'm sure.

There is a manufacturer's tolerance on stuff like this so they have to be reasonably accurate by law; I seem to recall they must be within 10% but I really don't know if that is the right figure. 22% is way out; what confidence do you have in the app? And why trust this over the speedo?

As mentioned on another thread GPS isnt accurate either .

 

I think the rules for testing for type approval are in this piece of legislation

 

EEC Reg 75/443/EEC.

Thanks for replies. I thought that if the GPS isn't accurate, I would in this case missed an exit with several kilometers if it is 10% off. I have used the same app on a VW T5 (The car I use at work). This car has slightly larger tyres than the stock ones. The readings in the speedometer on that car is only 1-2% lower than the readings in the SpeedView app.

I tested the app also with my Toyoa Avensis. The speedo reads approx 3-4% less than the app.

 

I have 14" rims on the CitiGo. If it is so that the tyres has the same profile on the 15" rims, that would in case explain the difference - at least a little.

 

Vidar

Hi all,

 

I downloaded "SpeedView" on my phone today, and checked the speedometer vs. GPS readings.

When the speedometer reads 80km/h, the GPS reads 70km/h. That is an error of 14%. Thus, fuel consumption would actually be worse than I thought.

Also, the tripmeter would display 14% longer driving distance than the car actually has traveled. Mine reads now approx 30 000km, but in reality it has traveled "only" 26 250km.

 

However, at 50km/h on the speedometer, the GPS reads 41 - which is 22% error... Is this normal?

 

Vidar

It might pay you to post a question in the VCDS section. With the Yeti it is apparently possible to "calibrate" the speedo to be more accurate.

 

Fred

Fred, I will ask my dealer about this. I hope they have the tools to calibrate. I have wondered why cars drive pass me even if i exceed the speed limit by 15 - 20% :-)

What size tyres are you running on the 14" rims?

Remember also that travelling up and down hills is a shorter distance to GPS. Pythagoras and all that.

How good is the app?

It all depends on how many decent satalites your app picks up too!

There is latency to deal with too.

Most GPS/satnav speeds with good connection are a few miles/kilometres an hour out to your speedo but they only calculate time/distance travelled and do not account for up and down hills but not as bad as you seem to be suffering.

And as mentioned above your tyre size, tread depth and tyre pressures all make a difference to the recorded speed.

Is this on your phone?

Edited 15 February, 201511 yr by Defenderben

What size tyres are you running on the 14" rims?

175/65 I think

How good is the app?

It all depends on how many decent satalites your app picks up too!

There is latency to deal with too.

Most GPS/satnav speeds with good connection are a few miles/kilometres an hour out to your speedo but they only calculate time/distance travelled and do not account for up and down hills but not as bad as you seem to be suffering.

And as mentioned above your tyre size, tread depth and tyre pressures all make a difference to the recorded speed.

Is this on your phone? There are some latency. It picks up around 15 satelites according to the app. The latency wouldn't be a problem as the app stabilize within very short time as I keep the same speed.

 

The app just use the GPS coordinates, and calculate velocity (More correct word I guess). Nothing different from Googge Maps I also use on the same phone. Very accurate, and poits out almost within 5-10 meters where I am. So the calculated speed, using the same satelites should be sufficient to find correct velocity.

 

There are plenty of straight roads where I live, so hills is not a problem.

 

I will use a watch to take the time between 10 lampposts along the highway. It is exactly 60 meters between them on the highway (And normaly 50 meters at other roads). I will keep the speedometer at 100 km/h and compare my calculations with the speedometer and SpeedView. Then I can confirm if SpeedView is accurate or not.

175/65 I think

That discounts any error attributable to the tyres.

"I think"?

If we knew for sure, we could calculate.

"I think"?

If we knew for sure, we could calculate.

Checked. It is 175/65 R14. The same on the summer tyres.

 

Edit: It helped a little to increase air pressure from 1 bar to 2.5 bar in the tyres, but not very much.

 

Vidar

From nothing to overkill then.

Better check pressures every three weeks or so. Correct pressures can be found from tank lid.

From nothing to overkill then.

Better check pressures every three weeks or so. Correct pressures can be found from tank lid.

2,5 bar is no problem. It saves more money on fuel than the wear of the tyres :-)

I find it strange that the pressure was so low. Actually 0.7 bar on the right front tyre... Guess I have to check that more often.

 

Anyways, I checked the speedo with the SpeedView with more than 5% difference after refilling the tyres. When I had 90km/h on the speedo, the SpeedView displayed 82km/h - almost 10% error. I think it's too much. Maybe I will put on some Donald Duck tyres next time - 175/90 R14 will finally make my speedo to display the correct velocity at 80km/h, hehe!

 

Vidar

Car weight is under 1000kg. 2.5 bar is quite a lot even for bigger car. And winter tyres works better if you allow them to flex. But, 2.5 bar is surely better than 0.7 bar.

 

I'm sorry I forget to check my speedo error last night. Maybe I remember today. To me your speedo error sounds acceptable now.

Edited 16 February, 201511 yr by Emil

It's probably important to add that the speedo app is out by about 3-4 mph, I downloaded this (assuming it's the same one) last night to test it

I did a registered 30mph according to the app but my speedo was saying I was doing almost 35mph, it to me felt like I was doing 35mph and not 30mph, moral of the story is I trust the speedo more than an app

I use Ulysse Speedometer for Android.

When the speedo shows 120 km/h, Ulysse shows 110km/h.

Speedo 100 km/h, Ulysse 92-93 km/h.

Speedo 60 km/h, Ulysse 55 km/h.

Speedo 20 km/h, Ulysse 18 km/h.

Someone else may calculate percentages.

Today I compared my app with a tachograph we have as a testinstallation in one of our service cars (also a VW T5). This is a calibrated and approved device which measures the correct velocity.

The app is pretty much spot on. When the tachograph displays 100 km/h, my app displays 100km/h. The speedo on that T5 displays about 106km/h.

 

So, then I assume the app, with its GPS coordinates and calculations is as correct as it can be.