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Car Speedometer Accuracy vs GPS: Understanding the 5 km/h Difference

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  • #31 21350381
    BANANvanDYK
    Level 42  
    Has no one noticed that in "smart" instrument clusters, i.e. microcontroller-controlled and with stepper motor-driven clocks, the hands do not rise perfectly to the "0" dash when switched on? Besides, meters in diagnostic mode have the possibility to check the correct functioning of the indicators, e.g. indication of 50 km/h, 100 km/h.
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  • #32 21350394
    Mastertech
    Level 27  
    This is why it is so difficult to put a pointer on a clock with a stepper motor,
    As the author's colleague told me, it is not the same for him as for everyone else.
    In newer cars which have a factory GPS, neither the speedometer nor the navi shows the actual value from the GPS, but only after conversion according to the formula which has already appeared here in the topic.
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    #33 21350640
    Anonymous
    Level 1  
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  • #34 21351385
    Ordine
    Level 24  
    For me, depending on the phone - of which I have several - it varies between 3km/h from the speedometer to well over 10. It all depends on how realistic the GPS fix is for the phone. Chinese inventions have the biggest problems with this.
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  • #35 21351395
    kulmar
    Level 32  
    0 ≤ V1 - V2 ≤ (V2/10) + 4 km/h
    where V2 is the speed actually reached by the vehicle and V1 the speed reported on the clocks.

    This formula has a simple interpretation: for high speeds, the error in the speedometer display (excess) must not exceed 10% of the actual speed; for low speeds, the error must not exceed 4km/h.
  • #36 21351843
    urkotrebor
    Level 21  
    When it comes to overestimation of speedometers in new cars there is nothing to discuss because it is a fact .
    My observations indicate that it is from 5 to 10 km / h and I have not encountered that the speed is underestimated (unless the meter is damaged), the subject did not occupy me so much to check exactly, but I have the impression (not supported by measurements) that American vehicles do not have this affliction (maybe someone can confirm or deny it) .
    In my opinion, however, this defect is not a problem because I know about it and because I do not have a temperature gauge in my car I built myself a device that reads the speed from the ABS and some other values .
    The reading from the ABS in my case seems to be accurate and coincides with the speed tables in my area .
    Now to the point , after the introduction of the new fine tariff I observe how the average speed has dropped drastically , because the meter overestimates (5-10) , because I will pay (10 and more) .
    Traffic jams form in my area, journey times have sometimes increased by 100%, CO2 production has increased because it is still 2nd gear in gusts to 3rd gear, leaving the subdivision is a problem.
    The fact that fewer people die on the roads, but what the future holds (lung diseases, heart disease, osteoarticular problems) .
    And although there are fewer victims, there are more bumps and collisions, because at low speed people become less careful .
  • #37 21356268
    Anonymous
    Level 1  
  • #38 21356298
    James596
    Level 28  
    But there are not that many "no limit" sections in Germany. On city ring roads you're often doing 80 km/h, and there are the ubiquitous roadworks.
  • #39 21356361
    Anonymous
    Level 1  
  • #40 21356378
    Anonymous
    Level 1  
  • #41 21356456
    user64
    Level 34  
    But what does the lack of speed limits have to do with the amount of fines? I'm having a great time there, it's legal to check how much the factory has given.
  • #42 21357083
    Anonymous
    Level 1  
  • #43 21357628
    Anonymous
    Level 1  
  • #44 21368859
    BANANvanDYK
    Level 42  
    >>21348931 .
    I have read the R39 provisions in detail.
    Interestingly, mopeds should have counters that overestimate by 10% +4 km/h offset, just like in cars.
    In addition, the meters on mopeds must not have a scale exceeding 80 km/h.
    Meanwhile:
    Close-up of a moped speedometer with a maximum scale of up to 120 km/h. .
    This is a 50cc scooter I used to make. The model locked in the worst possible way, that is, structurally in every component, so difficult to unlock. When I rode it, I was surprised to find that it rides like a bike. It's standard for the meters on scooters to overestimate, but I didn't expect it to overestimate so much.
    By the meter it was pulling 50-55, max 60 km/h. I checked my speed with the GPS and it turned out that it was going the legal 45 km/h, max. 50 km/h.
    Basically, the error of the meter readings exceeds the allowed norm, and the red range on the dial of 100-120 km/h not allowed by the regulations is not even possible with this engine.

Topic summary

The discussion centers around the accuracy of car speedometers compared to GPS readings, highlighting a common discrepancy of about 5 km/h. Participants note that speedometers are designed to overestimate speed due to regulations, particularly in the EU, where the formula 0 ≤ V1 - V2 ≤ (V2/10) + 4 km/h governs acceptable error margins. Factors influencing speedometer accuracy include tire wear, vehicle calibration, and the type of speed measurement technology used (analog vs. digital). Users share personal experiences with various vehicles, indicating that while some speedometers may show a consistent overestimation, others can vary significantly. The conversation also touches on the implications of these discrepancies for driving behavior and traffic regulations.
Summary generated by the language model.
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