Tire Size

[Paw Paw]

Just 2 quick questions. One on tire size . I have 275 x 65 x 18 tires on my truck at this time . I used the formula in the Gryphon manual to calculate the tire size and came up with the number 2482 with a 3% squish .
My truck came originally came with 235 x 75 x 17 tires . Tire size in the Gryphon was 2356 - If I remember correctly .
I have changed the size in the Gryphon a couple times and have got different results each time .
Can anyone fix me up with the correct tire size number for my tires and maybe how you did it .
I am waiting on my custom tunes . Should I go ahead and download the Pegasus software now while I am waiting .
Thanks in advance
Paw Paw