A couple quick questions...
Does anybody have the constant for some BFG 265s? And if not and I have to calculate it do you round the number or not? I figure the number isn't gonna come out even so what then.

 

I sent you a PM, but just in case, these are the instructions I have:

Recalibrate Your Speedometer after Changing Tire Size

There is no tire size/code chart because tire size vs. actual tire dimensions is different between manufacturers. Even between the same tire size and same maker there will be a difference in actual size between the different tread designs.

The Ford calibration equation is:
20186 / tire height in inches = some number, then: some number / 0.6666 = program code

Example:
Start with 20186, divide by actual tire size in inches. Divide again by 0.6666.

You want to use a rolling measurement to get your actual tire height. (If you try to measure the tire in the driveway, use conversion charts, or anything else you will end up with an inaccurate reading again). Use your rear tire since the sensor is located there. Mark the ground and your tire and roll forward 3 times marking the ground each time. (I ran over a spot of oil at a local gas station and measured between my tread mark prints), then divide that number by three to get the average length of one revolution (this will protect yourself against a bad reading using just one revolution). You can then divide the length of one revolution by 3.14 to get actual tire height. Be careful in your measurements, a small amount will change the code. EX: 31.69" tire height is code 956, and 31.21" tire height is code 970.

Now, to program it into your truck:

Warning: You can only change the calibration 6 times without replacing the module.

To set the calibration:

1. Ground the single wire connector under the glove box it says PSOM (Programmable Speedometer Odometer Module). “Yes there is only one and it has a spade type plug on the end”. I used a wire with clips on both ends to ground the plug to a screw under the dash or try a test light and use the clip end to the PSOM and the other jam in a door hinge.
2. Now look at your speedometer on the face of your dash while sitting in the driver’s seat and there should be a "Reset" button and a "Select" button.
3. While holding the reset button in on the trip meter, turn on the ignition while the wire is still grounded.
4. Let go of the reset button. The speedometer display will sweep once and will show a code.
5. Push in the reset button and the existing code will be displayed with RECAL? (Mine said 976 RECAL?)
6. Now enter the new code you came up with (by dividing the rolling measurement by PI or 3.14) by pushing the “Select” button until it displays the new calibration code number. You may have to push “Select” a whole bunch of times until you get to your code. If you turn off the key at this point the original code will not be changed or any of the six lives will not be used.
7. To store your new code, press “Reset”.
8. Turn off the key.
9. Unplug the ground wire
10. To check the new calibration, use the mile markers on the interstate. Run an indicated 60 mph. It should take exactly 60 seconds to go one mile.

I don't remember who sent these to me, but I thank you again.