1. Attachments are working again! Check out this thread for more details and to report any other bugs.

  1. Steve Shepherd

    Steve Shepherd Junior Member

    Joined:
    Jun 1, 2013
    1
    0
    0
    Vehicle:
    2013 Prius
    Model:
    Persona
    The speedometer on my 2013 Persona shows high by 2 mph. Is this caused
    by the 17 inch wheels? I wonder if the dealer can reprogram for this?
     
  2. jdcollins5

    jdcollins5 Senior Member

    Joined:
    Aug 30, 2009
    5,131
    1,338
    0
    Location:
    Wilmington, NC
    Vehicle:
    2010 Prius
    Model:
    III
    No. My car is also 2 mph high with standard 15" tires. This is a standard for all manufacturers to not be on the low side.

    The car actually knows the correct speed for other purposes but displays high.
     
    TsKarma likes this.
  3. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,101
    10,035
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    This is about normal. You will find many speedometer error threads here on PC. The systematic bias in the high direction is an industry norm, and is (indirectly) required in some areas. An error spread is a fact of life, so the typical displays must be biased high so that the low end of the distribution does not violate local laws forbidding any car to read lower than actual speed. European market cars typically have a larger bias than North American market cars.

    Odometers do not have the same systematic error, at least these days, because it leads to class action lawsuits for warranty fraud.

    If you install an aftermarket engine monitor such as ScanGauge, you should find that the internal speed known to the engine's computer is much more accurate. Only the dashboard display contains this systematic bias.
     
  4. hlunde

    hlunde Member

    Joined:
    Dec 22, 2009
    419
    74
    1
    Location:
    NJ
    Vehicle:
    2010 Prius
    Model:
    III
    There are quite a few speed readouts set up by law enforcement these days. My experience after many "tests" is that the Prius reads about 3-4% high at 60mph, while both my Audi and Volvo are basically spot on. Perhaps some manufactures make their speedometers read high because they know that's what US drivers expect, while other manufacturers are obsessed with accuracy.
     
  5. Former Member 68813

    Former Member 68813 Senior Member

    Joined:
    Oct 3, 2010
    3,524
    981
    8
    Location:
    US
    Vehicle:
    Other Hybrid
    Model:
    N/A
    The bias also helps with maximizing MPG, as people are driving slower than they think. This with the optimistic MPG readout makes a lot of people happy.