How to use FORScan to adjust tire size

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FORScan
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How to use FORScan to adjust tire size

Post by FORScan »

If vehicle tyres have been changed to another size, vehicle configuration has to be adjusted to keep speedometer readings correct. The change is quite simple, but has few nuances so here is a detailed step by step instruction for this process.

Note 1: this article is actual for new vehicles with so called Economized Central Configuration (ECC). ECC means that some memory blocks in BdyCM module of the car are reserved to store parameters that are used by several modules. Tire Size is one of such parameters. Although it has been stored in BdyCM, it is actually used by PCM, TCM, AWD, ABS etc. There is some specific in managing ECC, reviewed below.

Note 2: Tire size is programmed as tire circumference in mm. You need to use any tire size calculator to convert from normal tire size to circumference in mm. For example, this one:

https://tiresize.com/calculator/

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WARNING: Modifying configuration parameters in Module Configuration (As Built format) function and using As Built spreadsheets is not a recommended way. Configuration layout may be different between models/years and using wrong layout may cause problems. Recommended way is to use Module Configuration that lists configuration parameter in a human friendly way. This manual explains how to do it on example of Tyre Size.

1. Obtain an adapter that works with Ford. We recommend OBDLink EX.

2. Download FORScan for Windows from our official site:

https://forscan.org/download.html

3. Install Extended License, you can get free 2mo one as described in our FAQ:

https://forscan.org/faq.html#qlic2

4. Setup the adapter (should be done automatically by Windows)

5. Connect to the vehicle.

6. Go to Configuration and Programming and run BdyCM Module Configuration

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7. FORScan will open the list of all configuration parameters available for the BdyCM module:

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8. Number of parameters is quite significant, it may be hard to find necessary one. So please use the filter field at the top of the work area to filter the list by key word 'tire':

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9. Select the “Tire Circumference” parameter in the table and open the edit dialog box either by clicking twice with left mouse button on the parameter, or by pressing "Edit selected" button:

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10. Change the value as you need:

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and press OK button.

11. Press Write to write the changed parameter to ECU:

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12. FORScan will ask to confirm the change:

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Press OK to confirm.

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:

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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:

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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:

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Note: some modules have a harcoded range (min…max) for the tire size. So if new value is out of the range, module will not learn it but throw P1635, U0422 or similar DTC. Unortunately, in such cases we have no choice other than adjust the new size to be in the range (so, find maxmum circumference accepted by the module).
wpdriggs
Posts: 2
Joined: Thu Aug 20, 2020 7:15 pm
Vehicle: F350 2020, 6.7

Re: How to use FORScan to adjust tire size

Post by wpdriggs »

295/65R20=2799 mm followed instruction all worked well except the MPH is still off, speedometer says 60 but going 57.7 @ 75 GPS has me at 72.7 2020 F350 Platinum SRW 6.7 Powerstroke.. any ideas?
wpdriggs
Posts: 2
Joined: Thu Aug 20, 2020 7:15 pm
Vehicle: F350 2020, 6.7

Re: How to use FORScan to adjust tire size

Post by wpdriggs »

295/65R20 = 2686mm is correct, GPS has me 1, 2 10ths faster than speedometer but i am good, cleared codes as in the directions no CEL
275/65R20 was my factor tires and 2631mm was my default value not what is calculated with the site in post


Hope this helps,
condonsons
Posts: 4
Joined: Wed Jan 06, 2021 9:52 pm
Vehicle: F350 super duty 6.7 power stroke 2017

Re: How to use FORScan to adjust tire size

Post by condonsons »

My 2017 F350 came with 245/75/17, I put new tires on 285/75/17. I went to change the mm and it was a little different than shown above, it had 4 sizes preloaded to choose from. I choose the 275/65/20 and it gave me an error, I also had to change the mm as well. But it gave me no DTC codes but I did find it in the PCM and TCM where I changed the mm there as well. GPS speed to speedometer is 70 to an GPS actual of 69.4. Worked well :)
CEOwen
Posts: 1
Joined: Sun Jan 17, 2021 10:30 pm
Vehicle: Ford F150 , 2.7, 2018

Re: How to use FORScan to adjust tire size

Post by CEOwen »

my 2018 came with 245-70-17 and i put 275-65-18's on it. Used forscan with 2558 as the cir mm. Now my speedo is off 2 mph slow. I'll never get a ticket now! I tried changing the number to 2550 to see if it would be closer... but then it wouldn't shift to 10 gear again, and it was still off 2 mph.
What say y'all?
thanks so much!
wingwah
Posts: 1
Joined: Wed Jul 15, 2020 3:01 pm
Vehicle: Ford Escort China C490,1.5L Duratec Ti-VCT(110PS)F

Re: How to use FORScan to adjust tire size

Post by wingwah »

After reading the post,I realised how to fix the tire size.thank you
NotAnExp3rt
Posts: 1
Joined: Mon Feb 22, 2021 9:19 pm
Vehicle: 2018 F-150 Lariat 5.0

Re: How to use FORScan to adjust tire size

Post by NotAnExp3rt »

Is there a better way than guess and check to find the top of accepted range?
goss8037
Posts: 1
Joined: Sun Dec 01, 2019 5:53 pm
Vehicle: 2019 F150 3.5EB

Re: How to use FORScan to adjust tire size

Post by goss8037 »

What is the largest tire circumference allowed on a 2019 F150 without throwing the U0422 code?
McJanDK
Posts: 8
Joined: Tue Jan 12, 2021 7:24 am
Vehicle: Fiesta Vignale, 1.0 Ecoboost 140HP, 2020

Re: How to use FORScan to adjust tire size

Post by McJanDK »

you have to x0,967 to get the correct data in mm after calculation... like mine 205/45R17 = 1935x0,967=1871 and this is for ford Fiesta MK8 from 2020
I enter 1870 and then its worked
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mrmrva
Posts: 10
Joined: Sun Aug 18, 2019 5:44 pm
Vehicle: Fiesta, 1.0 EcoBoost, 74kW, 2014

Re: How to use FORScan to adjust tire size

Post by mrmrva »

@McJanDK

Did your speedo change reading after tire size change? Did you check that?
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