Reset vehicle software with new tire size

[Jack RJ]

I recently installed Bridgestone Blizzak 275/55 R20 snow tires on the OEM rims of my 2018 Expedition 4x4. The OEM tires are Hankook 275/55 R20 tires. My speedometer now reads 6-7 mph fast when comparing to a GPS reading (at 50 mph). With the Hankook tires the speedometer mph reading matches the GPS reading (again at 50 mph).

I had the Expedition to a Ford dealer who said that the vehicle software can be reset for tire size. However, the tech was unable to find the setting, so no change has been made. Seems like this should be a routine matter for a Ford dealer. Has anybody had the software adjustment done, or familiar with how it is done?

By the way, the info I found says that the Bridgestone Blizzaks have a diameter of 31.9 inches, while the Hankooks have a diameter of 32.1 inches. The data I found says the Hankooks turn 647 revolutions per mile, versus 653 revolutions per mile for the Bridgestones. So, the difference in diameter does seem to explain the mph discrepancy.

My original problem when I first put the Bridgestone tires on is that there is apparent "surging" or "slipping" when the transmission is put into Sport 4x4 mode using the rotary dial on the center console.

 

[st381183]

Don’t think there’s a user level screen to change tire diameter in settings. I would find a new tech.

 

[Black]

It can be done changing a few things in ForScan.
https://www.expeditionforum.com/posts/372245/

 

[Uturn]

According to the tire specs you should only see 1/2mph difference at 60mph. You may want to double check your GPS, they do glitch at times. Are you also sure they put the correct tires on? According to speed difference you gave, the new tires would have to be 4 inches in diameter larger to see a 6-7mph difference at 50mph.