TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Speedometer off by -1 MPH

Discussion in 'Model S: User Interface' started by mmh, Aug 27, 2014.

  1. mmh

    mmh Member

    Joined:
    May 11, 2014
    Messages:
    122
    Location:
    SLC
    Curious if anyone else has noticed the speedometer being off by -1 MPH, e.g. car says 60MPH but in reality is going 59MPH. I can verify this with both GPS and those radar speed limit sign things.

    6046_61MPH_CLSTuPg.JPG
     
  2. qwk

    qwk Model S P2681

    Joined:
    Dec 19, 2008
    Messages:
    2,817
    Yes, my car also reads 1mph high.
     
  3. astrotoy

    astrotoy Member

    Joined:
    Jan 24, 2013
    Messages:
    266
    Location:
    SF Bay Area
    #3 astrotoy, Aug 27, 2014
    Last edited: Aug 27, 2014
    Mine is exactly on, when it is stopped!

    On my 2007 Lexus LS460L the car reads about 3 mph fast for speeds above about 20 mph. In the Lexus group there was talk about challenging Lexus about their warranty, since it is both time and mileage based and the odometer shortchanges the warranty on mileage. No issue with unlimited Tesla mileage.
     
  4. R²B

    R²B All Star

    Joined:
    Aug 24, 2014
    Messages:
    340
    Location:
    Waddell, AZ
    I'd venture to say that the car is more accurate than both commercial GPS and speed limit signs.
     
  5. bollar

    bollar Disgruntled Member

    Joined:
    May 1, 2013
    Messages:
    2,240
    Location:
    Southlake, TX
    Unless the car gets its speed from GPS, the speed displayed comes from wheel revolutions and is subject to change as the tires' circumference reduces due to tread wear.
     
  6. Johann Koeber

    Johann Koeber Member

    Joined:
    May 1, 2012
    Messages:
    663
    Location:
    Nuremburg, Germany
    Well - according to German law the speedometer can only have a tolerance to the high side. It can never show a speed lower than the one you are driving.

    The formula is

    actual speed < speed shown by speedometer < actual speed + 10 % plus 4 km/h

    Source:
    § 57 Par. 2 StVO
    Anlage zu § 57 Par. 2 StVO

    I assume there are similar laws in other countries.

    The MS has the most accurate speedometer of any car I have so far driven - I love it. Until I knew this, I had to pay one (small) speeding ticket. But now I know!
     
  7. AnOutsider

    AnOutsider S532 # XS27

    Joined:
    Apr 3, 2009
    Messages:
    11,923
    I've noticed a small discrepancy, but never really tested it to get an accurate number.

    All of our previous cars (German) were off as well, and it scaled as you went faster). There was "talk" on some old forums about German automakers doing this because they didn't want to be held liable if a ticket was issued saying they were going faster than the speedo indicated.

    Don't know how true that is, but almost immediately I noticed the Model S always seemed to indicate a speed closer to real speed than past cars.

    *edit* and it seems Johann ninja'd me and confirmed the chatter.
     
  8. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

    Joined:
    Jul 12, 2012
    Messages:
    4,493
    Location:
    Maine
    US law is similar.

    PS The Prius is a big fat liar on speed and fuel economy.
     
  9. Tommy

    Tommy Member

    Joined:
    Mar 3, 2010
    Messages:
    880
    Location:
    The great OC
    Not a scientific measurement, however I have driven by many portable radar speed display trailers and my car's speed always shows at least one mile higher on the display than what the speed sign shows.

    My other cars also show I am traveling faster than what the radar displays show, so it's not just Tesla that does this. Personally, probably a good thing due to the ease at which the S gets up to speed (and beyond).
     
  10. ecarfan

    ecarfan Well-Known Member

    Joined:
    Sep 21, 2013
    Messages:
    10,319
    Location:
    San Mateo, CA
    All the cars I have owned have read high except my Porsche 356's which read low under 35mph and high above that. The Model S seems to be more accurate than most.
     
  11. mmh

    mmh Member

    Joined:
    May 11, 2014
    Messages:
    122
    Location:
    SLC
    I just want to add; The Tesla has the most accurate speedometer of any car I've ever driven. I am just curious if anyone else noticed the speeds consistently off by 1MPH. I'm trying to determine if it's a margin-of-error thing, or if it's purposely wrong by Tesla.

    //On a side note, I have a BMW K1200S motorcycle which has always been dead accurate.
     
  12. ecarfan

    ecarfan Well-Known Member

    Joined:
    Sep 21, 2013
    Messages:
    10,319
    Location:
    San Mateo, CA
    Not only are most car speedos way off, but my BMW R1150RT was way off as well.
     
  13. tezzla

    tezzla Member

    Joined:
    Jul 14, 2013
    Messages:
    544
    Location:
    SoCal
    So, top speed is only 129? :biggrin:
     
  14. Paul Carter

    Paul Carter Active Member

    Joined:
    Apr 27, 2013
    Messages:
    1,456
    Location:
    Vancouver, BC, Canada
    I notice my car has a 2km faster reading than the speed zone radar signs which are around here. So that's just above 1 mile, so seeing the same thing here.

    So now what, I do some fancy math for cruise control... speed limit + 10% + 2km.
     
  15. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

    Joined:
    Mar 24, 2013
    Messages:
    4,219
    Location:
    Denali Highway, Alaska
    Let's work through the logic here:

    IF

    THEN is the following also true?:

    Speedometer on by +1 MPH

    ???!!!:biggrin:
     
  16. Park2670

    Park2670 Member

    Joined:
    Feb 17, 2013
    Messages:
    324
    Location:
    Utah
    My BMWs were always off around 4%. 1MPH seems much better.
     
  17. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    12,751
    Location:
    Texas
    The roadside radar almost always shows +1 mph, the few times when it doesn't show +1 it's zero.
     
  18. physicsfita

    physicsfita Member

    Joined:
    Jan 20, 2014
    Messages:
    424
    Location:
    Ann Arbor, MI
    Maybe I just got lucky, but I find that my Prius' speedometer reads high by about 1/2 mph, and the lifetime fuel economy display understates the mileage by about 1 mpg -- seems pretty darn good to me!
     
  19. Vger

    Vger Active Member

    Joined:
    Apr 10, 2009
    Messages:
    1,682
    Location:
    Salt Spring Island, BC, Canada
    This is my experience as well. I was just watching this during a long road trip. Given the Elon design ethic, I would imagine that they calibrate the speedometer to be 0.5 mph high, just to be legal, but to be otherwise as accurate as possible!

    I really appreciate being able to rely on the speedometer as accurate, as well as the incredible stability of the cruise control!
     
  20. green1

    green1 Active Member

    Joined:
    Mar 25, 2014
    Messages:
    4,105
    Location:
    Calgary, Alberta, Canada
    Speedometers on all cars read high from the factory. Modern cars less so than older ones as accuracy of the components is easier to guarantee now, but always high. It gives the manufacturer some wiggle room so as not to break the law stating they can't read low. (It also saves them from owner lawsuits when someone gets a speeding ticket!)
     

Share This Page