When changing your tire size, you need to fine-tune your programmed tire size so that your car will match with your particular tires. Here’s how to do it using the Ford As-Built Tire Calculator and FORScan:

Step 1  

Enter the following details of your tire size (Mustang & F150 - Rear, FWD cars - front): Section Width, Profile, Rim Diameter

For Example:

P235/50R17

Section: 235  Profile: 50:00  Rim Diameter: 17.000

Step 2

Set BCM line 726-12-01 to the following using FORScan:

xxxx 0B16 xxxx

*x's mean leave the value that's already present.

Alternative/Optional Way to Fine-tune Tire Size

Optional Step 1

Compare the speed indicated in your speedometer with the speed indicated in your GPS.

Use the speedometer needle and have it dead center over an MPH hash at the highest reasonable speed (e.g. 75mph) while in cruise control on a leveled surface. Use a GPS that readout MPH in tenths. Normally, GPS won’t instantly provide your speed rather it shows your speed averaged over intervals. GPS will still provide a highly accurate reading for as long as your speed is constant.  

Then use FORScan to read the hex value of your car for BCM line 726-12-01 and get your baseline. The current hex value in your vehicle is found on the second block. If line 726-12-01 reads xxxx 0856 xx for example, the 0856 would be your current value.    

Example Figures:

Speedometer MPH: 70   GPS MPH (tenths): 80.0  Current Hex Value: 097c

Optional Step 2

Set BCM line 726-12-01 to the following using FORScan:

xxxx 0AD7 xxxx

*x's mean leave the value that's already present.

Step 3 (Final Step)

Using FORScan, run the "Module initialization/Relearn vehicle data" procedure for the PCM ( also TCM if necessary). This will update your PCM and get rid of the P160A DTCs that may appear when you change your tire size.

This is how the process looks like:

*Special thanks to the online community who have created the original resource

In order to configure your tire size using FORScan, you will need a reliable OBD2 adapter. These are our featured OBD2 adapters that work flawlessly with FORScan. 

Note: For FORScan coding modifications, we recommend using the OBD2 USB adapter for it provides a more stable connection.