How to: Recalibrate Speedometer with Forscan for 2021 Bronco

[Chritaka]

I have the same tires. What a pain to balance.

Yeah, they took some weight to balance and they weigh 80 lbs themselves, but they look amazing in 37". They're so aggressive, so close to an MT, but super quiet on the road. So far I really like them and glad I went with them over the Baja Boss MT's, at least right now.

Sponsored

 

[Dmk08]

So I am running BFG Ko2 315x70x17 F150 Raptor spec. Based on that https://tiresize.com/calculator/ said I should input 2741. When I put these in with Forscan my speedo is about 2.5 MPH higher than my GPS speed consistently. Does anyone have these tires and run a different setting?

 

[sn1088]

Go back and read little further back in this thread. Use the suggested number given by a member. It’s a 2,6xx range number. Your numbers are too high (regardless of the calculator you used, that number doesn’t translate to Forscan/Ford).

 

[redone17]

I always find that the number that works in Forscan is about 4-5% less than the mm calculations that tiresize.com or otherwise states that the tire circumference is.

 

[Cameront9]

So I am running BFG Ko2 315x70x17 F150 Raptor spec. Based on that https://tiresize.com/calculator/ said I should input 2741. When I put these in with Forscan my speedo is about 2.5 MPH higher than my GPS speed consistently. Does anyone have these tires and run a different setting?

What i've been seeing almost 2" less is more accurate, also depends a little on your set up. So mine are 285/75/17s, 34" tire with circumference of 2700mm, but the circumference that I settled on that made the speedo accurate was 2565mm, or 32.15 inch circumference. That worked for my friend too who has 315x70x17 K02s, I don't remember the exact mm they used but it was around what a 33" would be. I also noticed that the factory default size was equal to a 30" tire when my big bend came with 32s.

 

[Dmk08]

What i've been seeing almost 2" less is more accurate, also depends a little on your set up. So mine are 285/75/17s, 34" tire with circumference of 2700mm, but the circumference that I settled on that made the speedo accurate was 2565mm, or 32.15 inch circumference. That worked for my friend too who has 315x70x17 K02s, I don't remember the exact mm they used but it was around what a 33" would be. I also noticed that the factory default size was equal to a 30" tire when my big bend came with 32s.

Good Info! If you happen to talk to him ask him what he set with the K02s! I'm at 2741 so I have to figure out if I need to go up or down. I'm guessing down?

 

[zorander70]

35/17 r70 TAKOs on my 2023 WT. I set the mm at 2600. GPS indicates either right on or slightly slower (0.5-1 mph). I could tweak it a bit more but I would rather err low than high. When I set the mm to the calculated 2745, the mph was skewed ~5.6%.

 

[Eric L]

Just make sure after you change the tire size to force the TCM and PCM to relearn and do the reset of the DTC, then you should not have any error messages:

13. Now we have discrepancy between tire size values known by PCM and TCM and new value stored in BdyCM. So we have P160A DTC in TCM module and P0610 in PCM module:

14. In order to remove the discrepancy, we need to force PCM and TCM to “learn” the new value from the ECC. We can do it using Module Initialization/Relearn vehicle data functions for PCM and TCM module:

Note: some cars may have other modules that require this operation, for example AWD, SOBDMC.

15. After running the Relearn functions, we need to reset the DTCs:

What is the max tire size that can be entered?

 

[Eric L]

What is the max tire size that can be entered?

I changed my tire size about 1.5 years ago when I put 37s on and didn't have any errors. I just changed my axle ratio to 4.88 (had Dana 60 installed a while ago) and changed my tire size back to 2800 and still getting errors

 

[sjax42]

This worked for me also for 37x12.5R17 Mickey Thompson Baja Boss A/T on my ‘23 Wildtrak. However, I set the circumference to 2775 as several stated speedo was .5 mph off or so at 2760. It took 2775 fine with no issues/errors. I haven’t had it to 80 yet, but it is accurate up to 65 mph so far. I confirmed across 2 apps, one being Waze.

Thanks for the great info in this thread!

Thanks for the info. 2775 was perfect for my Mickey Baja Boss.

 

[FranklinCounty4Door]

In my recent experience, 2741 is WAAAAAY too big for the Sasquatch tires. I spent some time refining the number with both math and a GPS speedometer app and got to nearly perfect with 2579 as the circumference in millimeters for the take-off sasquatch wheels/tires I have on mine.

And… I went to the dealer to have the PCM relearn done.

Thanks for this! I tried 2579 for the sasquatch takeoffs and was way faster than the speedo at 60MPH. Then I tried the 2653 from the guide on page 8 of this thread and was 1.5-2mph off. 2579 put me going .2-.3 mph faster on gps than the speedo. Close enough for me! I was able to clear all my codes using the guide on page 8.

 

[FranklinCounty4Door]

Has anyone updated to Forscan 2.3.46 which was updated on 2/7 and tried the PCM relearn?

I just used 2.3.59 and the OBDLink EX and was able to clear all codes using the guide on pg8.

 

[TLO]

Here's a quick, informative vid on doing the recalibration.

 

[Calypso]

I just used 2.3.59 and the OBDLink EX and was able to clear all codes using the guide on pg8.

Just another testimonial . . . same version, same scan adapter, same successful result. PCM and AWD module DTC codes cleared without issue.

Switched out 315/70-17 OEM Territories to P285/70-17 Cooper Discoverer AT3 4S, used 2525 mm (was 2653) circumference (Thx um . . . @Tricky Mike ?)

As another data point, mine was factory set at 2525mm with 285/70/17s. This sounds way too small for 315s but I'm not arguing with what works.

and 35 psi (was 39 psi) TPIM settings. Speedo reads 1 mph over GPS reading, perhaps due to minor differences of LT vs P-metric spec. I'm good with it as is.

Took me a little while to get comfortable with maneuvering between screens, but once I figured it out, it was easy. Be patient, and backup the factory settings FIRST! Speakers are next, I appreciate the 6G community for such an informative and valuable resource.

 

[Tricky Mike]

Just another testimonial . . . same version, same scan adapter, same successful result. PCM and AWD module DTC codes cleared without issue.

Switched out 315/70-17 OEM Territories to P285/70-17 Cooper Discoverer AT3 4S, used 2525 mm circumference (Thx um . . . @Tricky Mike ?)

and 35 psi TPIM settings. Speedo reads 1 mph over GPS reading, perhaps due to minor differences of LT vs P-metric spec. I'm good with it as is.

Took me a little while to get comfortable with maneuvering between screens, but once I figured it out, it was easy. Be patient, and backup the factory settings FIRST! Speakers are next, I appreciate the 6G community for such an informative and valuable resource.

Dick is dead to me, nobody liked that guy anyway.

Sponsored