Speedometer displays slower than car

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Speedometer displays slower than car

Postby BlazeTool » Tue Nov 13, 2012 12:42 pm

If you want to know your "actual" speed, take your car to a mechanic that will calibrate and certify the speed. (In the States, AAA will certify speedometers).

Slight changes in tire size can make a significant change in speedometer readings.
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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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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.

Via my iPhone 3GS.
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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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Re: Speedometer displays slower than car

Postby AlanOfTheBerg » Tue Nov 13, 2012 3:48 pm

In the 25-40 range, Waze and my Fusion align nearly perfectly, taking into account slight variations due to instantaneous changes on accel/decel.
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Re: Speedometer displays slower than car

Postby loadbang » Tue Nov 13, 2012 2:30 pm

My little Mazda MX5 Miata and two Ford Focus speedo shows 70mph but Waze and my Garmin satnav show 63-65mph. I have tried holding an anemometer out of the window and Waze was correct. Cars are normally given -10% tolerance at max, also switching wheels and tires to different sizes can have an effect if the circumference is different. My friends Range Rover and Audi R8 match Waze perfectly.

iOS isn't accurate. You can only poll for a location once every 15 seconds plus it also use AGPS, DGPS would be the best way to get accurate readings.
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Re: Speedometer displays slower than car

Postby floppyrod84 » Tue Nov 13, 2012 1:01 pm

Also, speedometers are 10% too fast by design. This includes digital displays.

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Re: Speedometer displays slower than car

Postby sahirnsiddiqui » Tue Nov 13, 2012 5:22 am

My experience is that both Waze (& my old Garmin GPS) show speeds almost exactly 10km/hr slower than my actual speed.
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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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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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