Where to Change Tire Size in FORSCAN?

[pa-outdoorsman]

My truck is currently at the rail yard waiting to be delivered to my dealer. I have a set of 245/65 R17 Cooper Discoverer AT tires sitting in my garage to swap for the stock 225s.

I know Ford offers 235s as a stock option and the on board computer can be set to that size. I'd like to do that so my tire size will only be one off from the speedo rather than two.

Anyone here familiar with where on FORSCAN I go to see the tire size setting and adjust it? Thanks in advance for the help!

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[NoVaJimmy]

BCM data. Follow instructions for adding drive modes and you'll see the place to change tire size

 

[pa-outdoorsman]

BCM data. Follow instructions for adding drive modes and you'll see the place to change tire size

I've looked at those instructions many times. Is the tire size setting right on the same page where you enable and disable the ABS module and drive modes?

 

[NoVaJimmy]

I've looked at those instructions many times. Is the tire size setting right on the same page where you enable and disable the ABS module and drive modes?

From what I remember..... it's been quite a while since I added the drive modes

 

[RyaninWA]

I recently did this when I installed some AT3W in the same size. I found a couple interesting things and I will offer a solid bit of advice "write the number down that you originally find".

I used methods found on other forums for F150 owners and it more or less rang as "enter BCM, change tire size in mm, then reset and re-learn both the PCM and ABS modules which take the tire size directly from the BCM that you just modified.

The SNAFU for me came when I found that the PCM has an upper limit to the tire size that it will accept, and if you go beyond that it will throw and error and check engine lights on the dash. My new tire size ended up being almost 100mm larger than the number I had to enter to make the PCM happy. I did not try to drive to see if any change was made while the lights were on. I had not written down the original tire size, thinking that once I had gotten it changed I would never need it. I also was unsure what the limit on size was that the PCM would take.

The funny thing is that once I did the math on the FX4 tire, that size would not jive, nor would the base trim size. I was stuck and resorted to downloading an as-built of my truck and restoring the whole BCM to get back to the start. What I came to find that is strange, is that the number is designated in mm, and the number that my BCM had originally stored is well under any of the offered tire sizes by a lot. Makes me wonder if either there is some other calculation being laid on top, or the speedo may have been a bit off the whole time. I changed the value upward in increments of 10, resetting the ABS and PCM each time until the PCM started to kick back errors, then I went down 5 and called it good. It's better now being off about 2mph at 70, but I was originally about 5mph off.

 

[mav_kev]

I recently did this when I installed some AT3W in the same size. I found a couple interesting things and I will offer a solid bit of advice "write the number down that you originally find".

I used methods found on other forums for F150 owners and it more or less rang as "enter BCM, change tire size in mm, then reset and re-learn both the PCM and ABS modules which take the tire size directly from the BCM that you just modified.

The SNAFU for me came when I found that the PCM has an upper limit to the tire size that it will accept, and if you go beyond that it will throw and error and check engine lights on the dash. My new tire size ended up being almost 100mm larger than the number I had to enter to make the PCM happy. I did not try to drive to see if any change was made while the lights were on. I had not written down the original tire size, thinking that once I had gotten it changed I would never need it. I also was unsure what the limit on size was that the PCM would take.

The funny thing is that once I did the math on the FX4 tire, that size would not jive, nor would the base trim size. I was stuck and resorted to downloading an as-built of my truck and restoring the whole BCM to get back to the start. What I came to find that is strange, is that the number is designated in mm, and the number that my BCM had originally stored is well under any of the offered tire sizes by a lot. Makes me wonder if either there is some other calculation being laid on top, or the speedo may have been a bit off the whole time. I changed the value upward in increments of 10, resetting the ABS and PCM each time until the PCM started to kick back errors, then I went down 5 and called it good. It's better now being off about 2mph at 70, but I was originally about 5mph off.

Year old thread, but changed my tire size yesterday and had similar troubles with the tire circumference in the BdyCM being outside the spec accepted by the PCM on relearn. The largest I could get the PCM to accept was 2270mm. My factory BdyCM tire circumference was set to 2230mm.

FWIW I installed 235/65-17 Wildpeak Trails, which is a factory tire option, and the circumference is 2330mm, according to my calculation. The ABS module allows the selection of 235/65-17, so it's weird that the PCM wouldn't accept anything remotely close to the corresponding circumference.

At any rate, my speedo is still off 1-2 mph when compared to GPS, so I'm not sure the additional 40mm I was able to add made much of a difference. Totally livable, but still annoying.

 

[RyaninWA]

Year old thread, but changed my tire size yesterday and had similar troubles with the tire circumference in the BdyCM being outside the spec accepted by the PCM on relearn. The largest I could get the PCM to accept was 2270mm. My factory BdyCM tire circumference was set to 2230mm.

My experience was basically the same, and I think the same upper limit on size.

Eventually I got my Accessport reprogrammed for the Maverick and it has tire size adjustment. The highest size I was able to get to stick was 29.6 (it kept resetting the size of I went over) but oddly my speedo is within 1 mph on the highway with my 30.6in tires so I'm satisfied if not confused.

 

[RyaninWA]

2230 if I remember. They aren't set any different for the option tires. Mine is an fx4 though so maybe. The BCM doesn't accept a whole lot more increase. Mav_Kev pretty much detailed exactly my experience as well.

 

[jdmz]

2230 if I remember. They aren't set any different for the option tires. Mine is an fx4 though so maybe. The BCM doesn't accept a whole lot more increase. Mav_Kev pretty much detailed exactly my experience as well.

I was able to set to 2270mm (didn't try any larger) in the BdyCM module. There is also a tire size setting in the ABS module. Do I need to change that too?

First time around I had a weird P160a AWD module error that I cleared by resetting DTC and running the calibration via the PCM or something. I was freaking out that I destroyed the truck.

 

[RyaninWA]

The PCM and the ABS module receive their settings from the BCM so you do not change them anywhere else. You will have to perform the "relearn" which will cause the PCM and ABS modules to get new settings from the BCM. Go too high on the tire size though and the PCM/ABS get unhappy.

 

[BlueRaven]

My truck is currently at the rail yard waiting to be delivered to my dealer. I have a set of 245/65 R17 Cooper Discoverer AT tires sitting in my garage to swap for the stock 225s.

I know Ford offers 235s as a stock option and the on board computer can be set to that size. I'd like to do that so my tire size will only be one off from the speedo rather than two.

Anyone here familiar with where on FORSCAN I go to see the tire size setting and adjust it? Thanks in advance for the help!

speedometer will read spot on with those tires. if you did a search you would have found that out.

 

[AltoXTLfx4]

Ok. So I can go from 225/65/17 to 235/65/17, Chang in back and relearn and and pcm with NO discrepancy? That what I’m gathering?

 

[basepatrol5]

Anybody have any luck changing the tire circumference on a 2024 without getting a check engine/error light? I tried changing my circumference to from 2230 to 2270 as mentioned above, performed the re-learn, and still got an AWD error from the PCM. When I changed back to 2230 and performed the re-learn again, the error went away.

Maybe they changed some stuff on the '24s to make them harder to modify? I've had trouble adding Sport and Eco modes as well.

 

[basepatrol5]

I was able to set to 2270mm (didn't try any larger) in the BdyCM module. There is also a tire size setting in the ABS module. Do I need to change that too?

First time around I had a weird P160a AWD module error that I cleared by resetting DTC and running the calibration via the PCM or something. I was freaking out that I destroyed the truck.

Lol, I did the same thing, got the same AWD error, and was freaking the hell out as well. I had to change my circumference back to the stock value of 2230, re-run the PCM "Module initialization/relearn from central configuration," and then run a PCM "Key On Engine Running On Demand Self Test" to convince the truck that nothing was wrong and clear the AWD error.

I tried 2270, which others mentioned as "the upper limit that will work with no error," and still got the error. Had to go back to 2230. I'm in a 2024 FX4... maybe Ford changed something from the '22s and '23s to make the process different or disable it?

What was the step-by-step process you did to eventually get 2270 to work with no AWD error?

 

[EONR24]

Lol, I did the same thing, got the same AWD error, and was freaking the hell out as well. I had to change my circumference back to the stock value of 2230, re-run the PCM "Module initialization/relearn from central configuration," and then run a PCM "Key On Engine Running On Demand Self Test" to convince the truck that nothing was wrong and clear the AWD error.

I tried 2270, which others mentioned as "the upper limit that will work with no error," and still got the error. Had to go back to 2230. I'm in a 2024 FX4... maybe Ford changed something from the '22s and '23s to make the process different or disable it?

What was the step-by-step process you did to eventually get 2270 to work with no AWD error?

This is in the ABS module. Maybe this could be causing unremovable DTCs?

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