I don't think that's true. My XLT with 34s didn't automatically adjust. I had to use Forscan to set the circumference.

 

I just put my winter tires back on for a road trip north over Easter. Went from a 33 toyo mt to a 31 nokian hakk. Speedometer was spot on with my toyos and within 15 km it was spot on with the nokians. It must auto adjust.

 

It may. And with GPS and other technology, I don't see why it couldn't.

 

It certainly could, but I highly doubt it does. I know for certain my 2015 did not.

 

My 2016 came with a brand new set of 265/65R18s in it when I bought it used. Just changed it to 275/70s. Speedometer read 2mph fast with the old tires per 25mph radar signs locally, now reads dead on. It's a big jump from 31.6" to 33.2" diameters.

Ford is probably using rotation information from the ABS system to determine tire size, since tire diameter is important information for an ABS system. Our 2014 Honda Accord has no TPMS sensors, it uses the ABS system. If a tires rotation count isn't in synch with the others, it simply means the tire is losing air and its actual rotating diameter is becoming smaller and the ABS system trips a low tire light. Possibly the speedo error with the tiny tires was due to a size range to keep the program a practical size?
I'm not saying for certain they are, but it sure looks like it from here.

 

When I went from 32.1" to a 33.2" diameter, my 2021 automatically adjusted the speedometer, either using the trucks GPS or ABS system. I verified this with a GPS.

I reached out to a Ford master tech (friend of a friend) and he told me that he didn't have a way to reprogram the 2021 and newer F150 tire diameters.

 

Huh, I've tried resetting the tire circumference multiple times with Forscan following the instructions in the sticky on this forum and it never took. After 3 or 4 tries I just gave up and have lived with it ever since. Everyone makes it sound so easy, but Forscan is pretty fickle if you ask me.

I also tried adding the "Ford Performance" welcome screen via Forscan and it would work on the initial startup but as soon as I turned the truck off and back on again it reverts back to my original home screen. I gave up on that too after multiple tries.