Having the correct air pressure in your tires is very important for proper handling, a comfortable ride and of course, insuring the tires have proper contact with the road and don't over heat. Both under and over inflation cause well documented problems. Proper alignment is equally important but setting the pressures is the best place to start.
In order to get a realistic weight, insure that you have the coach stocked as you would for traveling, have the fuel tank full, the amount of water in the tank you would normally carry and the people on board.
Once the coach is loaded, it is important that you have it weighed. A 4 corner weight is best. Excessive imbalance across an axle should be dealt with. Try repacking the compartments and cabinets to get an even balance side to side if possible. Watch the loading end to end also.
Once you have the weights where you want them, use the highest weight on a wheel position and double it to use for the weight on that axle.
I have modified a spreadsheet that will calculate the tire pressures. It provides a good baseline but in no means is meant to replace due diligence in observing tire wear and heat. Always check tire pressures frequently and do "walkarounds" during trips to check the tires and the vehicle in general.
*8/24/18* The spreadsheets have been modified to revise the pressure exponent (n) in the equations and make it selectable. I have also added a calculation for sidewall deflection as excessive deflection due to underinflation is a major cause of heat and failure in tires.
Check with the tire manufacturer (website) to get the data to enter under 'tire specifications'. After that, enter the info from the builders plate on your coach and then enter the weights you have.
After you have run the spreadsheet with your data, manually use the highest wheel position weights from each axle and check the manufactures 'load vs pressure table' to insure the pressures calculated by the spreadsheet are reasonable. Understand that the dual pressure listed is per tire; the spreadsheet provides the calculated load per tire. Mistakes can happen; lets error on the safe side. This data is provided for your convenience; use at your own risk.
Also review the values computed for deflection to insure they are equal or above the factory maximum load value.
Click Here for the Excel spreadsheet in .xls format. (Excel prior to 2007)
Click Here for the Excel spreadsheet in .xlsx format. (Excel 2007 and up)
Click Here to open page 23 from the Yokohama Truck and Bus Radial Tire Sales and Reference Guide M-300-0410 explaining the tire contact patch.
Click Here to open an additional document on tire pressure with explanations and the effects of improper pressure.
You can save any of the above files by right clicking on the link and doing a 'Save Link As'.
The spreadsheet is 'Read Only' so once you have added your numbers, do a 'Save As' and give the file a name indicating your coach. This way the original file is available for future use.