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speedometer accuracy

Discussion in '2nd Gen. Tacomas (2005-2015)' started by malibu2a, Oct 4, 2011.

  1. Oct 4, 2011 at 9:15 AM
    #1
    malibu2a

    malibu2a [OP] New Member

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    We have a 2009 Tacoma. We use a GPS on long trips to new areas. The speed recorded by the GPS in on average 10% less than what the truck is showing. We have used the GPS in several other vehicles and the speed is dead accurate. The dealer says the GPS is wrong...they say the tires on the Tacoma are worn. Seems that it is never the Tacoma that is the problem. I have talked to the manufacturer of the GPS and they say that the tracking of the satellite is accurate within 3 meters and is real time. Also they stated that the size of the tires have no effect. Normally this wouldn't be a problem but the truck is a lease and we will be charged for the extra miles accumulated over the 4 year period of the lease. What do I do to get the dealer to take action on this. I have over 110,000 km on it now and another year on my lease which will incur at least another 30,000Km.:mad:
     
  2. Oct 4, 2011 at 9:33 AM
    #2
    aficianado

    aficianado Well-Known Member

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    GPS is the correct one.

    buy bigger tires?
     
  3. Oct 4, 2011 at 9:35 AM
    #3
    friction

    friction Well-Known Member

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    Mine seems accurate (based on comparison with my GPS) up until around 50-55 MPH...at "75 MPH" I am doing more like 71.

    That is with 265/75/16R.
     
  4. Oct 4, 2011 at 9:35 AM
    #4
    Maverick904

    Maverick904 Resident Fishing Expert

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    What size tires are you running. When I had my 265/70/16 my speedo read faster than my gps. Now that I have 265/75/16 they are dead on till about 65/70 ish.
     
  5. Oct 4, 2011 at 10:49 AM
    #5
    Rodallg

    Rodallg Well-Known Member

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    My GPS is is dead on with my odometer, speedo reads wrong, on any trip I use the GPS.
     
  6. Oct 4, 2011 at 11:03 AM
    #6
    David K

    David K Well-Known Member

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    With a 1" taller tire (265/75-16) over stock (265/70-16) your speedometer will become accurate with the GPS (satellites don't lie)... Before the taller tires... the speedometer read about 3 mph more than I was really going (does help you from getting a ticket)... at Hwy. speeds.
     
  7. Oct 4, 2011 at 11:18 AM
    #7
    TacoCat

    TacoCat Look away, I'm hideous!

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    I went from the stock 265/70/16s to 255/80/17s and have noticed as my speed increases the GPS and my speedo differ more and more. At slow speeds it's not much but if my speedo says I'm doing 55mph my GPS tells me I'm doing 59 or 60. I've learned to live with it.
     
  8. Oct 4, 2011 at 11:57 AM
    #8
    maineah

    maineah Well-Known Member

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    My 2011 is spot on my 2002 VW is off by at least 3 MPH my old 97 Taco was off 3 MPH both of them read more then the actual speed but the mileage was correct. I'm going with the GPS. I think a good part of it was to keep the manufactures out of the middle of disputes over speeding tickets.
     
  9. Oct 4, 2011 at 4:12 PM
    #9
    AndrewFalk

    AndrewFalk Science!

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    Speedo reads high so that you don't get tickets and sue Toyota. (You think you're going 60 MPH, but you're actually traveling at 57 MPH).

    And The size of the tires absolutely affects the speedo.
     
  10. Oct 4, 2011 at 4:24 PM
    #10
    Mlrwerks

    Mlrwerks Well-Known Member

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    3mph less than GPS at any speed above 20mph.
    Also shows 3mph less than those mobile "slow down" units that the village sets up.
     
  11. Oct 16, 2011 at 5:54 PM
    #11
    Doc Foster

    Doc Foster Well-Known Member

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    Slightly taller 265/70/17 ARE Z series cap.
    My 2012 tacoma with the stock 265/65/17 also has an inaccurate speedometer.
    Speedo reads 55, GPS reads 53.
     
  12. Oct 16, 2011 at 5:57 PM
    #12
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Moderator

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    The speedo is off a bit, but the ODO is accurate. Dont worry about the miles.
     
  13. Oct 16, 2011 at 6:10 PM
    #13
    WV150

    WV150 Well-Known Member

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    I have used the same gps in two toyotas a subaru and two fords and they all showd 1 mph faster than the gps.I tend to think the gps is wrong as it is unlikely five different vehicles would be wrong.On one ford it showd 1 mph faster but if you compared your miles on the interstate mile posts over 100 miles the truck only recorded 94 miles.The mph and the miles driven did not match.Gps can be wrong also.
     
  14. Oct 16, 2011 at 6:19 PM
    #14
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Moderator

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    GPS isnt wrong. IIRC, THey are accurate within a couple tenths of a MPH.
     
  15. Oct 16, 2011 at 9:57 PM
    #15
    JKD

    JKD Well-Known Member

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    Speedometers read fast. The manufacturer does that on purpose, they don't want a statistical distribution around the actual speed, because that means that about half of the people driving an indicated speed limit will be speeding.

    Every car I've ever tested with GPS or milepost timing has read slightly faster than the actual speed. My Tacoma reads about 5% fast. When it says 30, it really means about 28-29; when it says 60, it really means 56-57.

    Interestingly, the speed indicated on the scangauge is always within about one mph of the GPS indicated speed.
     
  16. Oct 20, 2011 at 7:44 PM
    #16
    4cyl4x4

    4cyl4x4 Active Member

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    Speedometer for mine is about 10% high, this means total mileage will also be 10% more. 60,000 mile on odometer is really about 54,000, this can reduce resale value. I started getting 26mpg, but with the 10% error that will be about 23mpg ( I was bragging until i figured the mpg did not change). A 32.6 diameter wheel will fix this, vs stock worn tire.
     
  17. Oct 20, 2011 at 8:02 PM
    #17
    AndrewFalk

    AndrewFalk Science!

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    False.
     
  18. Oct 20, 2011 at 8:10 PM
    #18
    BrokenTusk

    BrokenTusk I support a velociraptor free workplace.

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    Just got an OBD2 reader and it links to the GPS in my cell phone (Same one used by navigation program used in Garmon GPS)
    So heres the deal, theres a radar sign on my commute home from work on the highway..

    Speeds from:
    Highway radar
    My speedometer
    Theres the speed my OBD2 reader says (Matches gauge perfectly)
    Speed my GPS says.

    The radar sign and the GPS matched both saying I was doing 130, but the OBD2 speed reader and speedo said I was going 134 faster, they were wrong.
     
  19. Oct 20, 2011 at 8:34 PM
    #19
    knayrb

    knayrb Well-Known Member

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    Even with pure stock tires your speedometer will start to show faster than actual speed over time. This is because as the tread wears on the tires the diameter decreases and means it won't travel as far per rotation. A GPS will show the correct speed because it measures distance instead of counting tire rotations.
     
  20. Oct 21, 2011 at 1:46 AM
    #20
    David K

    David K Well-Known Member

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    Seems most of us are getting the same results.

    I am still waiting for an explanation on how the odometer is true when speedometer is turning faster than we are really driving? How does it know when we put a taller tire on to read the same as with the stock tire???
     
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