Setting arbitrary tire sizes for speedometer calibration

[jbroad]

For those of you with a 2017-2020 F150 (with 10 speed transmission) and are having DTC errors after writing your tire circumference. I've done some research and posted it here:
viewtopic.php?p=68424#p68424

[djbunge1]

When i do all the above and try to change my tire size on my 2018 f-150 platinum i always get the wrench on my dash and have not been able to get rid of it. when i put everything back to stock and relearn the wrench goes away. i am running a 2719mm or a 275/65/r20. i have tried both ways to input this in both the code and the tire circumference and have always got the wrench on the dash. can someone please help on why

[Jason1988]

PLEASE HELP!!!!! I have a 2016 F250 6” lift with 37x12.5x20. I’m am trying to correct the speedometer. I can’t get anything to work… I even seen were some Wednesday to change the tires to 35 inch and change the axle ratio and it will work, but it still doesn’t work. Everything will throw the codes and relearn doesn’t take them away nor does clearing DTCs. And even adjusting to so many different sizes and test driving it still does it change it at all.

[rbentnail]

I feel your pain! I went through the same thing only to find I had to remove Forscan from my computer then download the latest version. Everything after that worked perfectly.

[Jason1988]

Maybe that’s what I need to check is my forscan. I downloaded it a month or 2 ago.

[the70spoiler]

Ive tried inputting the tire size in the spreadsheet calculator and got my baseline size/hex figures to enter into BCM 726-12-01 after going up in tire size from a 65 series to 70. After trying to adjust from there using the gps speedo data change, it got me close to correct speedo vs gps but couldn't quite get it on the money. So, I literally jacked up one drive tire and measured the actual circumference, converted it to mm and took 96.7% of that figure as suggested. Converted this to hexadecimal and input the result in BCM 726-12-01. Cleared my DTC with no issues. I think. Seemingly dead nuts on now. However, when I looked at my off road menues it shows me as being in front wheel drive. I'll recheck it next time out and see if it relearns. It also had to relearn TPMS numbers so maybe, maybe not. No dash errors showing.
2018 f150

This is tomorrow, all good, the front wheel drive issue was me looking crosseyed at it or something, no problems. TPMS all reset on their own, speedo is better than stock was.

[james_pederson]

Hi, for some strange reason, I have the option to relearn the PCM but I do not have the option to relearn the TCM. Any thoughts? I downloaded the latest version of FORScan. Could this be that I don't need to relearn the TCM?

EDIT: Okay, it seems as though the latest version automatically does a TCM relearn when you run the PCM relearn. Would be nice if someone could verify this.

I was also curious about the mm value set in the BdyCM parameters. It seems that it is necessary to use the .967 conversion factor. My original tire size calculation was 2561 but my value after using the conversion factor (2561 * .967) came out to 2477. Should I be using the 2477 value?

EDIT: I went ahead and used the 2477 value (after the using the .967 conversion factor) and odometer reads perfectly.

Finally, I've seen many videos with settings for tire size in addition to the tire circumference. Is that still an option in the latest version? Or are the tire dimensions (i.e. 285/45/22R) no longer needed?

[lenko]

Dimensions are for all makes of tire and circumferences could vary a little and put a different code in. Actual tire circumference of your specific tire is more accurate for you. You could do it either way but circumference is better.

[ralwood]

I recently purchased a 2013 F150 lariat with 35x12.5r20lt tires. I was told by the dealer that the speedometer had ben corrected for the tire change, but now I am finding the speed is off by 13-14% which would closely match the difference in the tire diameter from the 35's with 2774mm to the factory 26560R18 listed at 2356mm. I have tried using the BdyCM tire circumference change in the BdyCM modifier (not as built) as well as changing the value in the 726-45-01 address which seems to be the correct address location. Neither of these seem to make any change in the speedometer responseeven after the PCM relearn is initiated. Is there something that I am missing?

[f-wolf]

I recently purchased a 2013 F150 lariat with 35x12.5r20lt tires. I was told by the dealer that the speedometer had ben corrected for the tire change, but now I am finding the speed is off by 13-14% which would closely match the difference in the tire diameter from the 35's with 2774mm to the factory 26560R18 listed at 2356mm. I have tried using the BdyCM tire circumference change in the BdyCM modifier (not as built) as well as changing the value in the 726-45-01 address which seems to be the correct address location. Neither of these seem to make any change in the speedometer responseeven after the PCM relearn is initiated. Is there something that I am missing?

Did you have a look here ???

viewtopic.php?t=15994

Also: https://youtu.be/ebRuUxJ4CfM