Clarity Speedometer Inaccuracies

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AnthonyW

AnthonyW

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Just got back from a 600 mile drive and I noticed that the GPS on my Waze app reported that I was going 1-2 mph faster than the cars speedometer consistently. Checked it out using a completely different phone and got the same result. Has anyone else noticed this and can some other folks check it out.


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Totally speculative: but I suspect the path on GPS has some extra wiggle because of tiny inaccuracies in location. This wobbly, rather than straight, path would make the distance traveled farther per time, and increase the calculated speed.

Just a guess however. Would not apply if Waze smooths the path to the map.
 
It is illegal in many countries for the speedometer to read under, so most will read between 0-10% over actual speed. The 1990s cars showed close to 10% high, so an indicated speed of 70 actually meant you were going 63.

BMWs all read 2.5 mph high or so. Each make is a little different, my Nissan's were really close to right on.
 
It's no guarantee of accuracy, but I've encountered numerous radar speed signs in the first 5 months, and my speedometer has been almost 100% in sync with them. Certainly no more than 1 mph difference on any of them.
 
vicw said:
It's no guarantee of accuracy, but I've encountered numerous radar speed signs in the first 5 months, and my speedometer has been almost 100% in sync with them. Certainly no more than 1 mph difference on any of them.
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Me too. On two occasions, both under 40 mph, speedo agreed with the police radar with display put out to try to slow down speeders. So it can’t be too far off.
 
You got a ticket for going 68 in a 65? You must have been pulled over by the biggest ahole cop imagineable.
 
I took some Scantool readings of the car a few weeks ago. I was looking over the raw data and noticed that there are significant differences between the car data and the GPS on my phone. Now it is possible that there is something wrong with the GPS on my phone, but it is a new iPhone X. The Scantool reports data roughly every one second, but it appears to me that the polling interval of the car odometer is both greater than one second and must reach a certain change in speed before it updates. Summary below and raw data is attached. This website won't let me upload an excel file, so I had to convert it to text. If you download the file and open with Excel it opens in a nice, easily readable format.

upload_2018-5-31_13-56-17.webp
 

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