get the four corner weights if possible, if not use the axle weights and add a bit more safety factor to your pressures.
I saw a noticeable improvement in ride and handling when I lowered my steer axle pressure accordingly...
Also, I learned from a tech support engineer at yokohama usa, that you can use load/pressure tables from any manufacturer for a given size. He told me that these numbers are standards that they all use, published through the "Tire and Rim Association"
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