Conflicting info about tire pressure

[4x4van]

Originally Posted by Ray,IN

Open the pdf, scroll down to page 13, last notation on the page.

Exactly. It does NOT say that you should never run less pressure than the placard. It says (my bold highlights):
WARNING:Serious or fatal injury may result from tire failure due to
underinflation/overinflation/overloading. To ensure correct pressure and vehicle
load, refer to vehicle owner’s manual or tire information placard in the vehicle."
Nowhere does it say to never run less pressure than the placard, and in fact, that idea directly contradicts their very detailed instructions on how to weigh your rig and how to use those weights to set your tire pressure correctly, and their page after page of load tables. They make it quite clear that since every RV owner loads their RV with different stuff, the only way to determine the correct pressures for your load is for you to know exactly what your load is; no other way.

[LPerry]

Originally Posted by Murf2u

"Design to the thousandth of an inch, measure to the 64th of an inch, cut with an axe."

We always say
"Measure it with a micrometer, Mark it with a piece of chalk, cut it with an ax."

As an engineer who has been responsible for making up numbers like this before (not tire pressures though), the placard is fine with some amount of margin on the original configuration (oem tires and such) and within it's intended usage. You can always fine tune things better to your situation by weighing and using charts and such. But generally speaking as long as you are under the number on the tire the risk is not enough air. Placard numbers will be softer ride, tire numbers will be max load capacity. Anywhere between is fine unless you want to go to the trouble to weigh it all and look at the charts.

I'm actually below the placard pressure with the wrong size tires that are a load range higher than stock, but all setup per tire manufacturer instructions... It's working great although I do avoid driving near buses full of nuns. [emoji6]

[4x4van]

To add even more smoke to the discussion, Goodyear/Bridgestone DOES have a publication that says to never go below what's on the placard. However, they ALSO somewhat contradict themselves:

"Always determine the correct tire inflation pressure based on actual loads on the tires. Use the tiremaker's recommendations (which you will find in load and inflation tables). Never use inflation pressures lower than those printed on the vehicle placard"

Personally, I believe that the statement about never going below the placard is more of a CYA from the lawyers than anything else, otherwise the tire manufacturers would have no need to publish load/inflation tables in the first place. After all, why bother? The placard's numbers are already based on the maximum GAWR's (so you should never need to go over that) and if you should never go under that...

Bottom line (for me, anyway), is that the placard reflects pressures recommended for the RV's maximum GVWR with the OEM tires. That is a very specific set of conditions/circumstances. However, since my RV is actually significantly under the GVWR, and I am not running the OEM tires (same size, but different brand and higher load range), I will instead go with pressures that the tire manufacturer recommends for the weight that I am carrying even if those numbers are less than the placard.

After all, Winnebago has no idea what my actual weight is, nor do they have any idea what brand/size/load range tires I am running. However, the tire manufacturer does know exactly what their tire will support, and the correct pressure to use in order to support that weight.

[Ray,IN]

Originally Posted by 4x4van

Exactly. It does NOT say that you should never run less pressure than the placard. It says (my bold highlights):
WARNING:Serious or fatal injury may result from tire failure due to
underinflation/overinflation/overloading. To ensure correct pressure and vehicle
load, refer to vehicle owner’s manual or tire information placard in the vehicle."
Nowhere does it say to never run less pressure than the placard, and in fact, that idea directly contradicts their very detailed instructions on how to weigh your rig and how to use those weights to set your tire pressure correctly, and their page after page of load tables. They make it quite clear that since every RV owner loads their RV with different stuff, the only way to determine the correct pressures for your load is for you to know exactly what your load is; no other way.

You missed the part of sentence highlighted in red.
A sentence consists of all the contained words, one cannot pick and choose to derive a meaning to suit the reader.

[4x4van]

Originally Posted by Ray,IN

You missed the part of sentence highlighted in red.
A sentence consists of all the contained words, one cannot pick and choose to derive a meaning to suit the reader.

I didn't miss anything, nor did I "pick and choose". I quoted the full section, and simply highlighted the parts that I wanted to emphasize. Your claim that "Michelin also says to never run less air pressure than what is stated on the Federally-mandated tire placard in the vehicle" is false. It is an interpretation that suits you; one disregards the parts that I highlighted (which is the reason I highlighted them), and one that I disagree with. Michelin does NOT specifically say that.