Detail Ford Speedometer Calibration

[bozowise]

I upgraded from the factory 17" wheels to factory sized 20" wheels.

I know that Ford can change the tire size to match since the tires are the factory option size.

I've read that it is changed in the ABS module.

Can someone outline the actual process of changing the tire size, my dealer doesn't seem to know. This way I can take them some directions..

[Clay Henry]

Wheel size won't effect the speedo - the tire diameter will. Are you going taller?

[Iqoair]

Most tire manufactures will list revolutions per mile, which is how Ford programs the information. They don't just enter that it's a 35" tire, or 37", etc. Tell them how many revolutions per mile and ask them to program it in.

[bozowise]

Maybe I should have added more detail. Yes I am going from 265/70R17 to 275/65R20 larger tire.

Respective revolution per mile is 638.1 going to 591.88 My speedo is reading slower then it should.



The 275/65R20 is an available option for the 09 trucks, and I know it can be programed.

What I need to know is directions on how to change it with the Ford scan tool. I just need to know where to go in the Ford scan tool to change the RPM because the dealer doesn't seem to know what I am asking about.

If I can take in the directions on "how" to change it I think I can get it done for free. If I have to drop it off and let them figure it out on their own I'm gonna have a bill.

[bozowise]

OK, got it done at a certified service center that has access to Ford's scan tool and PCM updates.

To change the calibration on my 09 you go to the "module programing" menu then to the "program parameters" there are lots of neat things you can do in the program parameters tab. One of them is "tire size" the factory tire size combos are listed with their respective revolution per mile settings.

Selected the new tire size and updated settings. Also found that the PCM had an available update so they did that at the same time. It kept the new tire settings after the flash as well.

They were not familiar with this option but there was a "police mode" in the program parameters. Wonder what that option allows you to change?