Ford As-Built Tire Calculator v3.0
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DO NOT REQUEST ACCESS TO EDIT THIS SHEET.

INSTEAD, FOLLOW BELOW INSTRUCTIONS TO MAKE YOUR OWN COPY WHICH YOU MAY MAKE CALCULATIONS WITH.
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TO USE THIS SHEET:
Go to "File" menu above and select "Make a copy", as follows:
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You will need to be signed into a Google account. You will be able to enter values and make calculations in your copy of the sheet.
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Program via nominal tire size:
This will get you close, however not all brands/models of the same nominal size (e.g. P235/50R17) have the same revs/mile, so it will not necessarily be dead on. Use the GPS truing method further down if you want to get your speedometer dead-on.
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Step 1: Enter your driven tire size (Mustang & F150 - Rear, FWD cars - front) Example P235/50R17 - 235 is the Section Width, 50 is the Profile, 17 is the Rim Diameter
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Section WidthProfileRim Diameter
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2355017.00
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Step 2: Using FORScan set BCM line 726-12-01 to the following: xxxx 07EA xxxx
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(x's mean leave the value that's already present.)
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Step 3: Use the "Module initialization/Relearn vehicle data" procedure for the PCM (and TCM if necessary) in FORScan to update your PCM and eliminate any P160A DTCs that may result after you change your tire size. This is what it looks like:
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Click Here
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Program via GPS truing:
Fine tune your programmed tire size to match your particular tires and car exactly.

Step 1: Compare the speedometer indicated speed to that of a GPS readout. Recommended that you use the needle of the speedometer and try to get it dead centered over a MPH hash at the highest speed reasonable (e.g. 75mph) on cruise control on as level a surface as possible. Your digital speedometer and cruise setting will be rounded to the nearest MPH, so it's less precise. Remember that GPS isn't capable of giving you instantaneous speed, instead it's averaged over intervals. However, if your speed is constant this GPS reading is highly accurate. Also recommended that you use a GPS with a MPH readout in tenths - Garmin GPS units for instance have a satellite info screen which shows MPH with this level of precision. Use FORScan to read the hex value in your vehicle for BCM line 726-12-01 to get your baseline. Your current hex value is the second block. For example if line 726-12-01 reads xxxx 0856 xx (ignore the x's) - 0856 would be your current value.
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Speedometer MPH
GPS MPH (tenths)
Current Hex Value
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8079.40A7F
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Step 2: Using FORScan, set BCM line 726-12-01 to the following:xxxx 0A6B xxxx
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(x's mean leave the value that's already present.)
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Step 3: Use the "Module initialization/Relearn vehicle data" procedure for the PCM (and TCM if necessary) in FORScan to update your PCM and eliminate any P160A DTCs that may result after you change your tire size. This is what it looks like:
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Click Here
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