Might be easier to calculate it based on how many turns on the tie rod. If the tie rod is at the mid point (fore/aft) of the wheel, a 0.025" movement in the tie rod would equal a 0.050" movement of the front edge of the tire. If (just picking a number, not sure what it acutally is) the tie rod is 12 threads per inch, a 1/3 turn on the tie rod would move it 0.025".
I'm thinking if you to use the method above, but adjust if for where the tie rod actually is in relation to the tire, and what the TPI is on the tie rod, you could get it pretty darn close.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)