I have been busy with re-calculating tire-pressure since 2007 ( not every day;))
This with the formula of the European tire and rimm technical organisation.
The TRA uses other formula wich gives lower pressures, I recently discovered.
My last made Excell-spreadsheet is for re-calculating tire-pressure when other tires are placed then the original.
http://cid-a526e0eee092e6dc.skydrive.live.com/browse.aspx/.Public/Recalculating%20tyre-pressure
The sheet gives , when you fill in everything right, always the correct advice-pressures for Heavy use and vacation use with tow-bar load. Those for normal use can go wrong if TRA formule is used for the plackard with advice-pressures. But nowadays the normal -advice pressures are mostly not given, so you dont miss them. You can always weight the seperate Axles with the load you use and add say 10% for measure-diferences. This you can fill in at "your own import".
from car you need;
1 Max axle loads ( on plancard under the motor hood or 1 of the door styles)
2 Maximum speed of the car ( in manual or estimate)
3 From the old advice-pressure plackard the advice-pressures for normal and heavy use for the original tires that are meanth for the specific car. Without this you will miss the normal-advice-pressures, so you can do without.
4 The camber angle only if above 2 degrees. This is when the alignment is like this /-. so mostly not needed.
from the tires. Example P195/65 R 15 90T
1 . The maximum load of the tire in example 90 is the load-index and stands for 600kg
2 . The letter that stands for the maximum speed of the tire. In example T stands for up to 190km/h
- The reference pressure or kind of tire. If you see somewhere on the tire side wall "at 250kpa"or "at 35psi"then this is always the reference pressure but you can select a kind of tire in the sheet. It is not the maximum pressure of the tire wich is with normal car tires higher ( 3 to 3.5 bar)
If there are questions or you might find some bugs ,then react here.
