'13 F150 tire size adjustment

[johnny248]

Hey guys

I had a Ram 1500 and the Trinity let me change the tire size for speedo correction by simply entering the tire size. Ex. 35x12.50x17. I now have a '13 Eco Boost F150 and the tire size adjustment is different. I guess it wants a circumference? I tried to calculate that for those 35" tires, but it always seems to be about 4mph off compared to the GPS. How can I figure the correct entry? Or what should it be? The tires are BFG A/T TA KO2 35x12.50x17 ,but according to the BFG specs its actually 34.5" diameter. I just would like to to be as close to accurate as possible for the speedometer reading.

I'm assuming the difference in the DS settings has to do with Ford's ECU vs the Dodge ECU, but the DS setting for the Dosge was much easier to use.

Anyway, if someone could help out that would be awesome!

[sohfast94]

Return the vehicle to stock. The latest update has the tire size changed to be like the dodges.

Yes it was a difference between the way ford pcm and dodge pcms do it but I made them the same.

[johnny248]

Awesome!! I will do that now. Thank you much!

[johnny248]

Updated the tool, set the tire size but the speedo is reading 4-5mph slower than the GPS. It is set for a 35" tire. What should I adjust it to to get the speedometer closer to correct?

Measure the actual tire height and input that into the tool.