Determining Tire Inflation PSI from Load Tables

[geoffff]

I already posted about this in a thread about airing down, but I've been asked to put this information about how I determine what tire pressure to run in this separate thread for easy searching/reference. So here goes:

My van has a sticker behind the driver door indicating what tire pressure to run, but this is for max load on the stock tire size. My Ford E-350 van says 80 PSI rear for LT245/75R16 tires:

I am currently running LT305/70R16 tires. I calculated the proper tire inflation for these tires and my van's weight using the "Load and Inflation Tables". All the tire manufacturers publish these tables which specify for each tire size what PSI is needed for a given (per tire) load. The specified PSI values should match, regardless of brand. Only the tire size matters.

Here is the 2020 Load and Inflation Tables from Toyo: Tire-Load-Table--Toyo--2020.pdf

And, here are a few older tables from other sources where you can verify if you like that the specified pressures do not vary from brand to brand:

• Firestone 2011
• Bridgestone 2006
• Rubber Manufacturers Association 2005

So, I weighed each corner of my van (regular body), while it was heavily loaded, and got the following values:

• Front L,R (lbs): 2100, 1950
• Rear L,R (lbs): 2800, 2650

When I look up my tire size (LT305/70R16) in the table, I see that for highway driving, I should be able to run 35 PSI front and 50 PSI rear. In practice, I usually round up to 40 PSI front and 55 PSI rear, just to have an extra margin of safety.

Here is a compilation I made of some common tire sizes I see people using using on Sportsmobile Ford E-Series vans:

The image above is an excerpt from an Excel spreadsheet I made from all tire sizes listed in Toyo's 2020 table: Tire-Load-Table.xlsx

Another bit of useful information given in some of the Load Tables documents are the Approved Rim Widths for given tire sizes:

-- Geoff

[marret]

Awesome, thanks much geoffff.

For our mods, please consider making this a sticky.

[BCam]

The site below is maintained by Roger Marble, a retired tire engineer. He is aka Tireman9 on Winnieowners.com and IRV2.com, both sister (RV Life) forums of Sportsmobile.com. Roger recommends adding 10% to the table values as a safety factor. His site has a ton of information on tires and tire safety that is as relevant to Sportsmobiles as it is to RVs in general:

https://www.rvtiresafety.net/2011/03...and-roger.html

[JWA]

This should be a sticky here, perhaps in the Engines & Drivetrain as well?