Thank you Tony, you're quite welcome, and, thanks for posting your tire sizes, so I could find out something for sure (not that I doubted you Lars)!
Here's what I get for the two tires using Bill's super easy calculator in Pegasus:
No Squish - Stock: 2559mm, 20's: 2545mm (a 14mm difference - about 0.55 inches, just as Lars said)!
5% Squish - Stock: 2503mm, 20's: 2498mm (a 5mm difference - only 0.02 inches)
7% Squish - Stock: 2480mm, 20's: 2479mm (only 1mm difference - virtually identical - only 0.004 inches for those of us who are metrically challenged)!
As I've said in other posts, the 7% rubber squish seems right for me with my 275/65R18's inflated to the recommended 40 psi. That's why I recommend it as a starting point.
Tony did not set his tire size when he loaded his tune - he bypassed the Custom Options!, so, the tire size was a "stock value" taken from the PCM's VID area. Clearly, Ford allows for "squish" too. And, interestingly, when squish is factored in, the two very different tires cover virtually the same distance in each revolution!
Again, thanks Tony, for confirming your tire sizes so I could explain what happened (to myself at least). This is a pretty neat bit of data to add to the database!
- Jack
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