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How to calibrate MPH on a Scan Gauge II

Discussion in '2nd Gen. Tacomas (2005-2015)' started by bluesttape, Aug 31, 2015.

  1. Aug 31, 2015 at 1:07 PM
    #1
    bluesttape

    bluesttape [OP] Well-Known Member

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    I see lots of posts about how great the Scan Gauges are. Lots of posts comparing to Ultra Gauge... and even more post selling the two items, but I can't seem to find info on how to calibrate the MPH. After getting bigger tires recently I know I am off a bit and if I understand this Scan Gauge II device it should help... As long as it's calibrated correctly. I hope to install it tomorrow.

    If there is already a thread, please feel free to yell at me... (and share the link) :fingerscrossed:
     
  2. Aug 31, 2015 at 2:29 PM
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    ranger098

    ranger098 Well-Known Member

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    I just used an app on my phone to give me my true speed, and somewhere in the scanguage you can enter a percentage off that your new tires are and it will calculate. For example, my speedo was 10% off so when my dash said 50 i was actually going 55. entered 10% into the scan guage and now it reads accurate. You might just trial and error the number you enter until the SC reads exactly as your phone app.

    You can download the manual online to find where to enter that %, im too lazy to post a link.
     
  3. Aug 31, 2015 at 2:59 PM
    #3
    Clearwater Bill

    Clearwater Bill Never answer an anonymous letter

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  4. Aug 31, 2015 at 6:22 PM
    #4
    bluesttape

    bluesttape [OP] Well-Known Member

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    so in theory, I would be 5.2%. Original is 265/65/17 new is 275/70/17. I get this # from the diameter difference shown as well as a manual calculation from the speed difference using the difference at 20mph and multiplying by 5 (to reach 100 aka 100% to get a true percentage).

    [​IMG]

    I feel all nice and spiffy with my basic math skills but can anyone confirm this is true?
     
  5. Aug 31, 2015 at 7:14 PM
    #5
    Clearwater Bill

    Clearwater Bill Never answer an anonymous letter

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    Why bother with the math?

    If you will run on cruise at 60 as reported by a GPS, you can then adjust the scan gauge as the instructions show starting on the bottom of page 16 in the link I gave you.

    If you don't have a GPS per se, but have access to a smart phone, there is an Play Store app (android) called GPS status that will work perfectly to give you a real time MPH. I'd assume there's an Apple version, but I don't know.

    Don't forget, your Odo is now hosed as well. You'll have inaccurate history from the tire change forward.
     
  6. Sep 1, 2015 at 9:46 AM
    #6
    edm3rd

    edm3rd Well-Known Member

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    Disagree with the above. Forget the speedometer, what you want to do is get the SG's odometer correct. Using either GPS/phone or by mile marker posts, run at least 25 or preferably 50 miles, starting with your SG cleared and one of your truck's trip odometers set to zero. Then calculate the error, and use the SG instructions to adjust. The reason for this is speedometer and odometer can and probably do have different % error. If you run 50 miles by gps/mile markers, and your SG shows either 49 or 51, it is off 2%, either + or -. Check the trip odometer you zeroed trip to see what your dashboard odometer accuracy is.

    Have had my SG for around 5 years, if you really want accurate mpg, this is the way to calibrate it - you need to know accurately how far you've been, not how fast you're going. Be also aware the error will change over time with tire wear. My oem tires lost a full inch when replaced, and were not down to the wear bars. 1"/30.5" = 3.2% error from tire wear alone. I check and recalibrate at least once a year.
     
    Last edited: Sep 1, 2015
  7. Sep 2, 2015 at 5:58 AM
    #7
    bluesttape

    bluesttape [OP] Well-Known Member

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    I got the Scan Gauge II installed and got the MPH correct by using an App on the iPhone (there were dozens). That being said, I am reading the above and it says to compare to my odometer, but correct me if I'm wrong, isn't my odometer wrong now that I have bigger tires?

    Thanks for all the help folks. Now that I got the super basic part of the Scan Gauge II figured out I hope to get to spend some time figuring out the rest in the next couple of days.
     
  8. Sep 3, 2015 at 9:37 AM
    #8
    edm3rd

    edm3rd Well-Known Member

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    To add to my post above - in the old days speedometer/odometer was fed by a cable, usually from the transmission. Different gears were available to adjust for changes in axle ratios or tire size changes and affected speedo/odometer reading exactly the same. Today most vehicles work off of a speed sensor and software that counts axle revolutions. Many manufacturers program the speedometer conversion 2-3 mph high to keep their lawyers happy. And, since software is involved, it is possible to feed the speedometer and odometer independently. My personal experience was speedo 2-3 mph high around 60 mph. Odometer error was about 1/2 miles off in 100 measured miles travelled.

    What is unknown is what the manufacturer uses for "tolerance" in the displayed/recorded dashboard data, such as odometer as accurate as possible on brand-new tires versus possibly set for half worn tires. Tire wear can easily account for a 3% error or more. This could also be reflected in the perception that "my mpg got better after 10,000 miles" - more likely it is due to tire wear.
     
    bluesttape[OP] likes this.

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