FORScan Tire Circumference Calibration Process

Alaska Steve · Aug 17, 2025

Since I could’t find a Ranger specific video to show the calibration process and I messed it up the first time I attempted it, I made a video of the last refinement that I made after correcting the errors I had made at first. I hope this 8min video saves someone else the time and frustration I went through last night (as evidenced in a separate post

). Don’t forget to read the video description. With that, here it is:

Calibration Process

AdventureLab · Aug 18, 2025

Alaska Steve said:
Since I could’t find a Ranger specific video to show the calibration process and I messed it up the first time I attempted it, I made a video of the last refinement that I made after correcting the errors I had made at first. I hope this 8min video saves someone else the time and frustration I went through last night (as evidenced in a separate post ). Don’t forget to read the video description. With that, here it is:

Calibration Process

I did my correction for the new 35" Nitto Terra Grapler G3's this weekend as well. I started with the diameter published by Nitto. Oddly, I had to plug in and adjust it several times before it matched my phone-based GPS speedometer. It ended up being a much smaller number (~150mm) less than what Nitto published. It's spot on now, but it did take a while to get it perfect.

joprato · Aug 19, 2025

@AdventureLab there is an inherent difference between GPS speeds and vehicle speed on dash and that’s mostly due to calculations refinements and differences between the 2 sources.
That being said, I think you’d be better off with the manufacturer number to make sure you do have the correct speed on the dash otherwise police radars could flash you while you thought you were below the speed limit…

you should be on the safe side for now having bigger tires and having calibrated for a smaller tyre I think, as your dash now thinks that the tyre is going faster than it actually is…

just to make sure you don’t run into unwanted trouble, you could probably make sure with a friendly cop that could measure your speed during a drive by with cruise control engaged (for precision purposes).

Cheers !

superj · Aug 19, 2025

you always want your speedo to read about 2mph lower than the gps does at 60mph. than you won't have trouble from police because of the differences in calibration between speedos and radars

joprato · Aug 19, 2025

Forgot that radars do require calibration too

TexasCajun · Aug 19, 2025

I wonder if I could change the XLT dashboard screen to display the Lariat display. I like having the large Tach over the small little RPM vertical bar. Anyone try anything like that yet with FORScan?

superj · Aug 19, 2025

i don't think we can on the smaller cluster. i have looked over lots of the forscan options but i don't recall seeing anything like that.

if you do find it though, be sure to put it up as i think it would be better, too

TexasCajun · Aug 19, 2025

So the Lariat has a bigger dash screen I did not think about that, they kind of look the same. I don't have anything to reference this on so I was hoping we could change it. Not a big deal though, if I do come across anything I will post it.

Alaska Steve · Aug 19, 2025

joprato said:
@AdventureLab there is an inherent difference between GPS speeds and vehicle speed on dash and that’s mostly due to calculations refinements and differences between the 2 sources.
That being said, I think you’d be better off with the manufacturer number to make sure you do have the correct speed on the dash otherwise police radars could flash you while you thought you were below the speed limit…

you should be on the safe side for now having bigger tires and having calibrated for a smaller tyre I think, as your dash now thinks that the tyre is going faster than it actually is…

just to make sure you don’t run into unwanted trouble, you could probably make sure with a friendly cop that could measure your speed during a drive by with cruise control engaged (for precision purposes).

Cheers !

I worked in the GPS industry for 20yrs, the last 8 of which I was a Product Manager interacting with the chip designers, core navigation engineers, embedded engineers, and test engineers. The precision products we developed were used in a wide variety of dynamic applications. I know for a fact that GPS speed is very accurate when at high steady speeds. Most systems use inertial measurement units that marry with the GPS to refine the error budget thereby improving performance. Cell phones typically use this technique because they use a very cheap GPS chip (it’s like a $25 component compared to the multi-thousand dollar receivers we built). I’ll take the GPS speed over factory every day.

joprato · Aug 19, 2025

@Alaska Steve thanks for that ! I knew GPS can be scarily accurate but I wasn’t aware about this level of precision in phones.

FORScan Tire Circumference Calibration Process

Alaska Steve

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AdventureLab

joprato

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superj

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joprato

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TexasCajun

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superj

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TexasCajun

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Alaska Steve

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joprato

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