Forscan and taller tire issue

[bent98]

I have a 2021 GT 500 with a Whipple and Lund tune, I recently swapped out my OEM tires for a drag setutp with forgeline rims, nittos up front and MT ET Street R in rear. 275/35/20 and 305/45/18 in the rear. I also have an MSS adjustable suspension and needed to install a stiffer black spring in the rear to get more lift to accommodate the taller MT tire in the rear and then had everything aligned.

I was expecting to get the famous lightning bolt after I did this and sure enough, I did. When driving my MPH were lower by 3MPH, You don’t get the lightning bolt until you drive it for 10 mins or so and it clears when you shut off car. Anticipating this would be an issue, I already purchased an OBDLink EX unit and forscan software with a full license.

You can’t read the factory ECU in Forscan if you have a tune unless you have the strategy codes which is not something the tuners would give out so I had to flash car back to stock. I flashed both the ECU and TCU to OEM. I adjusted the rear tire circumference in Forscan (BdyCM module configuration menu from the OEM setting of 2132mm to 2299mm I get this number when I plug the rear tire size into https://tiresize.com/calculator/ as per the Forscan instructions. The ECU saves new Circumference with no issue.

Here’s where it gets confusing. The Forscan instructions say “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 andP0610 in PCM module”
I don’t get that error, but then states 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.
There isn’t an option to do a PCM/TCM relearn in the config and programming menu.
Since I didn’t get the error, they described and I didn’t have the option for a PCM/TCM relearn, I flashed my tune back. Started car and drove. Now the MPH are about 3 MPH to high and after 10 mins I get the lightning bolt. Lightning bolt goes away when you turn off car.

Is there something I am doing wrong? I know many people have done this with keeping the stock tune but I can’t find one that’s running an aftermarket tune. Any help would be appreciated.
Link to instructions
https://forscan.org/forum/viewtopic.php?f=16&t=15994&hilit=How+to+use+FORScan+to+adjust+tire+size

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[GT500Flyer]

I thought that if you went back to stock tune and then made changes (saved) and the flashed back to the Lund tune, it would take? I have not tried it yet, but I thought that was how it was done.

 

[bent98]

I thought that if you went back to stock tune and then made changes (saved) and the flashed back to the Lund tune, it would take? I have not tried it yet, but I thought that was how it was done.

As mentioned , it did save the larger circumference but it doesn’t give me the option to relearn tcu and ecu which is why I am thinking I am getting lightning bolt

 

[GT500Flyer]

Does this video help? 3:20 mark.

 

[bent98]

Does this video help? 3:20 mark.

Looks like don’t do a sync either . They do take remove 1% of the circumference from the calculated number as ford does the with factory value

 

[GTFORMULA]

Not sure if this info will help you or not, but in hptuners there is a tab in the speedo settings to either use the ecm or bcm files. You can click that icon and use the pcm tunes numbers or leave it unlocked and use the bcm. Just going by memory on when I tuned my 2020 gt500.

 

[bent98]

Not sure if this info will help you or not, but in hptuners there is a tab in the speedo settings to either use the ecm or bcm files. You can click that icon and use the pcm tunes numbers or leave it unlocked and use the bcm. Just going by memory on when I tuned my 2020 gt500.

Thanks but the issue is not setting the Tire Circufrence, its reruning calbration between TCU and ECU.

Also, Its a Lund tune so I wouldn't have access to the information as its encrypted and don't have access to the strategy codes.

 

[Cgouzoulis]

So I had this same issue. First off, use the tire manufacturers tire height, not the calculator. (Mickeys run taller). Next, what line are you putting the height into? Theres 2 different places to input. I remember doing what you did and entering the MM, but it actually must be written in the BDM lines using a code that I found online. I'll try to find that info. In the end, I have started to not adjust and deal with the little light. I switch back and fourth between factory and drag wheels so it became a bit annoying to flash to stock, change forescan, then retune

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