Originally Posted by
khutch
You can do a curve fit to the data in a spreadsheet like Excel by adding what Excel calls trend lines to the graphs for M and B.
This old thread is just about the only place I have seen where somebody proposes a formula to fit Berto's tire pressure chart.
I have a different formula that is partly from fitting that chart but also based on some simple physics and geometry.
P = 120 * L * W^(-1.5)
P is tire pressure, in psi
L is single wheel load, in pounds
W is tire width, in mm
* is multiplication
^ is exponentiation
you can pretty much plug that formula into excel.
One interesting data point is the 102 mm Pugsley tire. My formula gives a pressure of about 11 psi while khutch gives 26 psi. khutch was just fitting the chart, which makes extrapolation difficult. Because I have a bit of physical analysis in there, extrapolation is more likely to work. 11 psi is about right for a Pugsley.