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Old 29th October 2021, 18:16   #1
geo.k23
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Default digital speedometer

how accurate is the digital speedo compared to the speedo in our cars just curious thanks
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Old 29th October 2021, 18:40   #2
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On all three of my ZTs it is spot on when compared to my road angel speed camera detector which uses GPS signals for speed, but on both my 75s it reads about 3mph higher than actual when cruising at 70. The speedo needle indicates 77mph when actually driving at true 70mph on the 75 too.
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Old 29th October 2021, 18:43   #3
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Not as accurate as the GPS but better than the analogue, having a hard time putting a number to it but say the analogue is 10% over GPS, then perhaps 5%. I'll try and remember to check next time I'm out and give you some real numbers unless someone beats me to it.

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Old 29th October 2021, 18:46   #4
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Quote:
Originally Posted by vitesse View Post
Not as accurate as the GPS but better than the analogue, having a hard time putting a number to it but say the analogue is 10% over GPS, then perhaps 5%. I'll try and remember to check next time I'm out and give you some real numbers unless someone beats me to it.

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Yes I noticed the digital is about 3or4 miles slower than the car Speedo
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Old 29th October 2021, 18:51   #5
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If I compare my speedo to speed over ground on satnav its 8 - 10% fast depending on speed travelling. The digital speed readout reflects what the sat nav reads so I have made the assumption that that is more accurate. Of course I could be completely wrong, be good to understand where the digital speed data is generated.
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Old 29th October 2021, 19:41   #6
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Quote:
Originally Posted by vitesse View Post
Not as accurate as the GPS but better than the analogue, having a hard time putting a number to it but say the analogue is 10% over GPS, then perhaps 5%. I'll try and remember to check next time I'm out and give you some real numbers unless someone beats me to it.

Regards
Sure I was reading somewhere where the accuracy of the GPS speed was questioned as it is not as high as people think. Sure it was down to it calculating the distance to travel between points, but doesn't take into account features such as gradient - think Pythagoras where you are travelling down the hypotenuse is further than travelling along the base.

The most accurate speed measurement would be physically measuring the distance travelled, through a doppler radar system or something.

In answer to the digital speedo though, mine also tends to show a couple of mph between that shown on the speedometer. I assume that it's the same signal that goes to both, and obviously there is a slight error in the digital to analogue conversion.
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Old 29th October 2021, 19:45   #7
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Analogue speedometers are always faster reading because they are required to always keep you within speed limit. Around 10% faster at true 30mph.

Digital relies on the same pulse source as the built in analogue, namely the reluctor ring in the wheel hub. I believe PhilT4 was the inventor.
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Old 29th October 2021, 19:54   #8
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Quote:
Originally Posted by KWIL View Post
Analogue speedometers are always faster reading because they are required to always keep you within speed limit. Around 10% faster at true 30mph.

Digital relies on the same pulse source as the built in analogue, namely the reluctor ring in the wheel hub. I believe PhilT4 was the inventor.
Sorry but although Phil-T4 is a wizard with electronics it was actually this guy we have to thank for the source: https://www.the75andztclub.co.uk/for...d.php?t=173990

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Old 29th October 2021, 20:56   #9
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my dash cam seems to be the most accurate followed but the digital speedo then the analogue speedo. I use my dash cam as my speedo so travel faster then what I would do using the cars two speedos and I have never been flashed or done by any speed camera as a result of using the dash cam.

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Old 29th October 2021, 21:14   #10
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will someone correct me if i am wrong. but is the correct wheel diameter the main player in this .. i did read somewhere that wheel sizes are set via the options on t4. 15/16/17 ... etc. if they are then that would account for the differences on some vehicles. ...
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