Speedometer displays slower than car

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Speedometer displays slower than car

Postby Lonewolf147 » Sat Nov 10, 2012 8:04 am

I did a search an found this thread from 2010, http://it.waze.com/forum/viewtopic.php?f=7&t=7147, but it didn't look like anything was decided or fixed.

My wife and I both have a Droid 4 (previously used Droid 1's) running the latest ICS. For the past several years that we've been wazing, the onscreen speedometer has always shown a speed 2mph slower than what our vehicles show. This has happened in every car we've driven, so it seems to be related to the Waze API and not the vehicle.

I've done the 'drive a mile' test and have confirmed my results that waze is reporting 2mph slower than my actual speed. I've also ran other GPS programs on my phone and they do show the correct speed of my vehicle. That tells me that my phone is correctly measuring my speed and again points to the Waze API as having an issue.

Has there been any other work or discussion of this issue that I'm not finding on the forum? Has this problem been duplicated with anyone else recently?
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Speedometer displays slower than car

Postby jasonh300 » Sat Nov 10, 2012 1:24 pm

Try your Drive A Mile test again. Divot based on mile markers in a different location.

Car speedometers generally read high to keep you out of trouble. My Chevrolet reads a few MPH higher than Waze, and my BMW reads about 5 or 6 MPH higher when going over about 45.

I've tested Waze against those "Your Speed" radar advisories and its pretty accurate.




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Re: Speedometer displays slower than car

Postby OldGnome » Sat Nov 10, 2012 4:15 pm

jasonh300 wrote:Car speedometers generally read high to keep you out of trouble.

This matches my experience exactly. I drive many different cars (I travel a lot for business) and have used a Garmin and now Waze. Whenever I have passed a "you are going this fast" sign, the speed on the Garmin/Waze matches very accurately to the sign. I have also done a driving test and the Garmin/Waze are more accurate than the speedometer.

Some vehicles (especially those with a digital speed readout) have more accurate speedometers than others.

YMMV
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Re: Speedometer displays slower than car

Postby crazed_out » Sat Nov 10, 2012 5:04 pm

This is true! A speedometer in a car is supposed to show that you're going faster than you really are. As much as up to 10%, but it' very different from make to make. Trucks (lorries) and busses have a speedometer that are much more precise than cars. Hence the reason for you driving and getting a truck or bus up close behing you. In my Volvo the difference is 5 km/h up to about 50 km/h then as much as 10 km/h between 70 and 120, after that I don't know because we're not allowed to go faster in Sweden. 8-)
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Re: Speedometer displays slower than car

Postby Lonewolf147 » Sat Nov 10, 2012 5:19 pm

jasonh300 wrote:Try your Drive A Mile test again. Divot based on mile markers in a different location.



OK, I'll try it again in a few different locations.

Thanks everyone else for the input. 8-)
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Re: Speedometer displays slower than car

Postby jasonh300 » Sat Nov 10, 2012 6:08 pm

Lonewolf147 wrote:
jasonh300 wrote:Try your Drive A Mile test again. Divot based on mile markers in a different location.



OK, I'll try it again in a few different locations.

Thanks everyone else for the input. 8-)


Oh, that's another point I wanted to make. The mile markers along the U.S. interstates are very inaccurate. I was checking them against my odometer one day and there would be .8 miles and then the next one would be 1.2 miles. They place the signs where it's convenient, so they're not always exactly where they're suppposed to be.
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Re: Speedometer displays slower than car

Postby islupepa » Sat Nov 10, 2012 8:01 pm

One of the reason for displaying wrong speed could be this conversion bug...viewtopic.php?f=15&t=7803&hilit=speed+conversion
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Re: Re: Speedometer displays slower than car

Postby dmcconachie » Sat Nov 10, 2012 8:11 pm

islupepa wrote:One of the reason for displaying wrong speed could be this conversion bug...http://world.waze.com/forum/viewtopic.p ... conversion

Firstly, it's not displaying the wrong speed. As mentioned above, your car almost definitely overstates the speed.
Secondly that conversion bug creates at most a rounding error. It's only noticeable because it means certain integer values are not displayed. Certainly not enough to be perceptible though!

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Speedometer displays slower than car

Postby rbthomp76 » Sat Nov 10, 2012 10:44 pm

I use Waze on an iPhone 4S. I also have a Garmin that run as well (guidance is pretty well covered). I have noticed that the speed on Waze (and thus the iPhone) is behind when starting and stopping. Once I get to a set speed, both the iPhone and the Garmin agree. My speedometer doesn't but that is a tire thing.

So, I think the GPS units in phones don't update as quickly as a stand alone GPS unit. But then against that is just a guess on my part based on what I've seen.

Perhaps that is what your seeing.


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Re: Speedometer displays slower than car

Postby Froggypwns » Tue Nov 13, 2012 4:33 am

My first hand experience shows Waze to often report 1 or 2 MPH slower than actual. My car will say 60, my Garmin will say 60, then on my Xoom tablet Google Nav will say 60, GPS Test will say 60, and Waze will say 58. Fire up my other tablet, Google says 60, Waze says 58. Even on my old Windows Mobile phone, it will say 58 on Waze and 60 on Google Maps.
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