Changing tire circumference (tire size) on Ford Transit 350 2019

[duksomi]

Hey guys,

does anyone know how to adjust the speedometer after mounting bigger tires? I'm planning on changing them tires from 235/65R16 to 225/75R16. This would only be only like a 4 % difference in circumference, but in Germany it's not allowed for the speedometer to show a slower speed than you're actually driving and it might be 1 km/h less... so e.g. me driving 100 kph via GPS the speedometer would probably only show like 99 kph.

I would mind since it would be just so little off, but I cannot register the car with this new tire size, if it doesn't fit. All those regulations in germany suck, but I want the car to be street legal, so I don't have a choice.

I found a option under BdyCM called "Tire circumference, mm : 2155" and these 2155mm would perfectly fit the tire size currently mounted, but if I change the value and make a test drive, the speed is still the same no matter what tire circumference I write. And it throws an error in the PCM-Module saying "wrong parameter in ecu" or somthing like that and the MIL is turned on. After changing it back to the original 2155mm, everything is back to normal.
Are there other things I have to change to get it working? I would prefer not having to buy an expensive device and plug it to the speedometer to simulate a different speed.

Anyways, thanks for potential replies.
Greets, David

[Jethro1999]

I am having the same problem with my 2023 awd changing to 245/75 R16 from stock. Changing the tire circumference results in both PCM and AWD DTC, which I am able to reset only the awd. The PCM DTC U0422 will not go away, and the speedometer still reads incorrectly as if no change was made to programming. Did you ever find how to resolve this?

[Don Ridley]

On the Superduty trucks you have the do a PCM/TCM relearn. I'm not sure it applies to Transit. Read the attached forum thread to get some ideas.

https://www.ford-trucks.com/forums/1642 ... n-5-a.html