OK, try a TS of 2709mm. That's just 35 x pi x 25.4 x 0.97 (which converts the circumference to millimeters and reduces it by 3% to compensate for "squish" (the flattening that occurs due to weight on the tires). That should be a close starting point.
You will load or simply reload your desired custom tune (you don't have to go back to stock first), and say "yes" to the custom options choice. Scroll to Tire Size, enter that value and hit [Enter]. Then, you MUST scroll to Gear Ratio (GR) and enter the rear axle ratio in your truck if the correct value is not shown. Both the TS and GR values you find in when you open the custom options menu are just "placeholders" and they may or may not be correct. When you've corrected both of these, scroll to "Done" and hit [Enter] to start the programming with these new values.
Check your speedo against a GPS if you have one. You actually want the dash speedo to read about 2 mph fast at 65-70 mph. This will make your odometer read correctly. If you use the speed readout on the Gryphon, it should match the GPS, and it will be slightly slower than the dash.
Make small adjustments to the TS to fine tune from that point.
Once you settle on the correct values and want to change tunes, scroll to "Load Previous Values" and hit [Enter] as the VERY FIRST STEP when you open the Custom Options menu. This will set the TS and GR to what you need. And, with the new tires, you will ALWAYS have to do this whenever you change tunes or your TS will be wrong.
- Jack
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