Conflicting info about tire pressure

[jmk909er]

I have a question about tire pressure. The manufacturers sticker inside the RV says my tire pressure should be 90 but on my tires it says 110. The tires are Michlen's and original to the RV. So what should I go by?

[LJowdy]

Without a doubt, the pressure stamped on the tires is the Maximum pressure. The absolute best way to determine tire pressure is to weigh the coach fully loaded. The best way is to weight each corner but if that's not possible then weight the front axle then drive onto the scale and weight the whole coach. Subtract the first weight (front axle) and you have the weight of the rear axle and since you weighed the whole coach, you now know how much the total weight is. Go here and it will tell you how much air should be in your tires
http://www.michelintruck.com/referen...tion-tables/#/

[wildtoad]

Go with what's written on the placard versus what's on the tire. The 110 it the MINIMUM pressure required to support the MAXIMUM weight the tire can support. It just so happens it is also the MAXIMUM cold PSI you could use. My opinion is the information on the tire is good information but basically useless.

You can use the GAWR and look on the Michelin tire chart, or get your unit weighed and use the same chart to get the correct PSI. But to keep things simple just use the placard.

[vsheetz]

Weigh (preferably four corners, but per axle is ok). Use manufacturer tables.

[hohenwald48]

Personally, without a proper scale weight, I'd go about half way between the sidewall max and the placard min. Assuming the vehicle is a motorhome.

It's been my experience that the placard minimum inflation pressure is right on the edge of being underinflated. I think the manufacturers go for that to soften the ride. Sidewall max is usually harder than necessary.

A proper weighing and application of the tire manufacturers weight chart is the best way to go.

If the vehicle is a trailer I'd go with tire sidewall max as ride quality doesn't really matter and it seems that most TTs come with minimum capacity tires.

[4x4van]

Originally Posted by hohenwald48

Personally, without a proper scale weight, I'd go about half way between the sidewall max and the placard min. Assuming the vehicle is a motorhome.

The placard is not the minimum. The placard assumes the RV is at it's maximum allowable weight. If the RV is not at it's maximum GVWR, then the placard numbers are too high. Also, the tire sidewall number is the minimum pressure for the TIRE'S maximum allowable weight, and has nothing to do with the actual RV the tires are mounted on. At 110psi, those tires will support 9350lb on the front (1350lbs over your max axle rating), and 17640lbs on the rear (2640lbs more than your axle rating).

If you have a suspicion that you are overloaded, then going halfway between the placard and the tire sidewall numbers is probably safe, but will be a jarring ride that handles terribly. If you don't suspect an overloaded condition, the the placard numbers, while safe, will likewise probably ride and handle "less than optimally". As has been said thousands of times on this and other forums; weigh the RV (loaded, ready for use), preferably 4 corner, but at least front/rear, and adjust tire pressure accordingly using the tire manufacturer's recommended pressures. Also, if you can't do a 4-corner weigh, assume a 53%/47% split on the axle and set pressure based on the 53% number; rarely are the numbers exactly the same side-to-side.

[Cat320]

Use the information from Michelin in post #2.

[MSHappyCampers]

As others have said, have your rig weighed, go to the tire manufacturer's website and get the recommended pressure for the weight, then add 5 PSI.

Remember, that's a "cold" pressure. Set it first thing in the morning before driving.

[CJ7ole]

Until you get your rig weighed (I suspect most never bother), use the placard numbers. They will be good up to your rig's maximum weight. Rig weight will vary depending on fuel, water, black, grey, LP tank fullness, number of people, amount of clothes and food and so on. You do want to weigh to make sure you get a feel that you aren't above recommended weight. It isn't just the tires, the whole rig is designed for a certain maximum weight. And if you pull a trailer or dolly, be sure to weigh with those attached and loaded.

[Ray,IN]

jmk909er; Use the Federally-mandated tire placard in the vehicle. NO tire manufacturer will recommend running less air pressure than what is on the placard.

Originally Posted by LJowdy

Without a doubt, the pressure stamped on the tires is the Maximum pressure. The absolute best way to determine tire pressure is to weigh the coach fully loaded. The best way is to weight each corner but if that's not possible then weight the front axle then drive onto the scale and weight the whole coach. Subtract the first weight (front axle) and you have the weight of the rear axle and since you weighed the whole coach, you now know how much the total weight is. Go here and it will tell you how much air should be in your tires
Load & Inflation Tables | Michelin Truck

Michelin also says to never run less air pressure than what is stated on the Federally-mandated tire placard in the vehicle.
"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."
source: https://rvsafety.net/Manuals/Micheli...dInflation.pdf

[4x4van]

Originally Posted by Ray,IN

jmk909er; Use the Federally-mandated tire placard in the vehicle. NO tire manufacturer will recommend running less air pressure than what is on the placard.


Michelin also says to never run less air pressure than what is stated on the Federally-mandated tire placard in the vehicle.
"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."
source: https://rvsafety.net/Manuals/Micheli...dInflation.pdf

I've just gone through that entire Michelin publication, and nowhere does it say what you are claiming. In fact, on the contrary; it spends several pages extolling the importance of weighing the rig and setting tire pressure accordingly, as well as pointing out the problem not only with underinflation, but overinflation as well. Care to explain?

[Ray,IN]

Originally Posted by 4x4van

I've just gone through that entire Michelin publication, and nowhere does it say what you are claiming. In fact, on the contrary; it spends several pages extolling the importance of weighing the rig and setting tire pressure accordingly, as well as pointing out the problem not only with underinflation, but overinflation as well. Care to explain?

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

[WeekendRVers]

Just curious, anyone with a Cornerstone? What do you use?

[Murf2u]

I can't help thinking about the old redneck engineering/ fabricating adage when I read threads like this about precise weighing and inflating;

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

The typical consumer grade tire pressure gauge is accurate to about +/- 5 psi.

Add to that the wide variance in tire temperatures given weather and road conditions which can pretty widely vary tire pressure, is it 40 degrees and raining, or 95 degrees with blazing sunshine?

The bottom line seems to be that what you see for cold pressure before you roll out in the morning has little relation to what the pressures will be for the rest of the day.