Tire pressure recommendations are mostly related to the maximum loads that a tire would see at any wheel position. The manufacturers suggested tire pressures are based on the amount of air pressure required in a given tire size/load range to support the maximum load (GVWR) at a particular wheel position.

Ideally, you could weigh each wheel of your van loaded the way it typically is, get a pressure/load chart from your tire manufacturer for your particular tire and inflate the tire to the pressure required to support that amount of weight. A manufacturer has to use the 'worst case' scenario (maximum load at each wheel position) to cover themselves legally.

I had posted this to the list previously:
"There is a formula for calculating the air pressure of
a non-standard sized/load rated tire using the tire
pressure recommendations on the sticker in the door
jamb. Since Vanagons have different pressure
recommendations front and rear, you need to use the
formula twice. Also, tire pressure recommendations
aren't the same for all Vanagon models, use the info
from the sticker in your van.

It is as follows:
[Original Tires Max Load Rating] * [Sticker�s
Recommended P.S.I.] / [Original Tires Max P.S.I.] *
[New Tires Max P.S.I.] / [New Tires Max Load Rating]"

Good luck,
Tim

"Chris S." <mrpolak@YAHOO.COM> wrote:
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.

TJ Hannink
Goldibox - 1987 Vanagon Camper, Wolfsburg Edition
1981 Bluebird Wanderlodge, FC-33
Winter Park, Florida
http://home.earthlink.net/~tjhannink/
http://groups.yahoo.com/group/wolfsburg_campers
http://photos.yahoo.com/tjhannink [Vanagon] Album
FAVOR website:  http://home.earthlink.net/~clubvanagon

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