Setting arbitrary tire sizes for speedometer calibration

[snowman]

I found this for my 2016 F350 XLT Dually, in the BCM under 726-45-01 if this will help others.

I have been able to adjust my Speedo using the spread sheet and putting in new tire size. Still trying to fine tune it, but I think I may have to live with it being off 1 MPH one way or the other.

Thank you OP, for taking the time to put this together.

Edit: I was able to dial in my speedo. On my setup with 255/80R17 BFG KM2. The BCM line 726-45-01 reads xxxx-09AE-xxxx.
Hope this may be helpful to some one in the future.

[Randy2015]

720-45-01 is where mine is on my 15 F250

I'm trying to recalibrate the speedo on my 2001 f250 superduty for the 35x12.50r17 tires that are on it. PROVING to be difficult to do as I am not certain where to find it or how to do it wi th forscan. Any help would be appreciated.

[kmoney25]

Guys, I'm running 35X12.5X20 Toyo A/T II on my 2019 F250. I'm trying to dial in my speedometer using the good spreadsheet and line 726-12-01, but I'm still 6mph off. Has anyone had any success with a 17 and up 250 and the same tires I'm using?

[aawlberninf350]

On my 2000 F350 V10, I was able to change the value of rotations per mile in the ABS config. I also set the PCM to re-learn.

Interesting, did that change your speedometer? I would have thought that the sensor on the trans output shaft would be used.

Worked like a charm. Speedometer reads correctly now. It reads the speed from the ABS sensor on top of the differential.....Just like my '85 F350 Cummins.

On my 2002 F350 7.3 I changed the Tire RPM in the ABS module. Did not see a way to get the PCM to re-learn. I chalked that up to having a chip on the PCM, but it could be a gas/diesel difference. If speedo recalibration does not work after I get some better testing I'll post back.

[lenko]

Which particular line in the ABS module refers to the tire rotation?

[mattdobey]

720-45-01 is where mine is on my 15 F250

I just bought a 2014 F250 Lariat with a 6.7 about a month ago, and I knew that the tires on it didn’t match what the sticker inside the door said.

After a little research, I found out that among some of the other cool things I could use FORscan for, I could also adjust the speedometer. (Remember that with great power, comes great responsibility!!!) Last week I drove a long stretch of flat road and compared the truck’s indicated reading with a GPS speedometer on my phone and found that the GPS speed was consistently 5 - 6 mph below the speedometer. Using the “Ford As-Built Tire Calculator v3.0” spreadsheet referenced above I was able to change the As-Built values shown below to “calibrate” the speedometer to my liking.

BdyCM Register - Status - Tire Size - Register Value - Result - GPS Speed Difference
726-45-01 - Factory As-Built - 275/65R20 - **** 0A46 **** - Result ~ -6.0 mph Below Speedometer
726-45-01 - “Calibrated” - 285/60R20 - **** 0A12 **** - Result ~ -1.0 mph Below Speedometer

After I changed the tire size in the BdyCM As-Built I had the DTC “P160A - Control Module Vehicle Operations Reconfiguration Error”. Once I ran the PCM “Module Initialization / relearn vehicle data” and jumped through those hoops as shown in the “Truck Stuff - Correcting Speedometer/Tire Size in Forscan (15-17 F150)” YouTube video, the DTC cleared, and my indicated speed vs. GPS speed is within my tolerance.

[01xc600]

I can't believe people are trying to correct for a 2mph difference!
My speedometer is almost 10 mph off at 70mph and I think it's affecting how the truck shifts as well.
I can't figure out if Forscan can even help my situation.
Does Forscan work as far back as 2003 for a Ranger? Everything I seem to read is saying no.
I'm driving this vehicle daily so I'd rather not take a chance possibly screwing something up.
Anyone?

[kamil_m]

does anyone have the spreadsheet link for all the tire sizes?

I found this for my 2016 F350 XLT Dually, in the BCM under 726-45-01 if this will help others.

I have been able to adjust my Speedo using the spread sheet and putting in new tire size. Still trying to fine tune it, but I think I may have to live with it being off 1 MPH one way or the other.

Thank you OP, for taking the time to put this together.

Edit: I was able to dial in my speedo. On my setup with 255/80R17 BFG KM2. The BCM line 726-45-01 reads xxxx-09AE-xxxx.
Hope this may be helpful to some one in the future.

[Dordogne]

does anyone have the spreadsheet link for all the tire sizes?

The spreadsheet is here, but it's kind of a cluster with how many people are using it at any given time. I suggest you make a copy of it in your personal Google Drive.

https://docs.google.com/spreadsheets/d/ ... edit#gid=0

[litian520]

very good