The only truly "correct" tire pressure is that which causes the
tire to evenly distributes the load across the tread width as it
contacts the pavement.

If one assumes that this is achieved at maximum load and
pressure as specified on the tire sidewall AND that this
relationship is linear and proportional, then indeed the
"correct" pressure may be calculated by the following formula:

Max load/max pressure = current load/current pressure

The above works fine in a static or a constant-load environment.

I think the best solution is use a pressure which achieves best
handling characteristics and monitoring tread wear patterns
closely in order to correct problems early.

In my experience I discovered that using tire pressure near the
max specified by tire manufacturer resulted in best handling and
wear characteristics.

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Chris S.'85 Westy Camel -> http://www.knology.net/~vw/vws/camel/ '84 Westy Hershey -> http://www.knology.net/~vwghost/hershey/ '01 NB TDI -> http://www.knology.net/~vw/Beetle.jpg