Tire pressure

[MNtraveler]

Originally Posted by GA_Boy

I don't care what air pressure the door sticker says. I set air pressure COLD according to my gross weight and tire rating.
I suspect that in Skielberts case the 61# may have been MAX for a smaller tire.
It could also be based on the vehicle gross weight and the current tire (Less load range).
Marvin

The tire pressure on the manufacturer's sticker is likewise based on the size and type of tire and the GVWR. That should always be followed unless one is going over the GVWR it has changed the size or type of tire. They know what they are doing, in consultation with their tire suppliers and industry standards.


Land of 10,000 Lakes
2016 Forester MBS 2401R
Nights camped 2016: 32; RV to date: 35

[Airdale]

Originally Posted by MNtraveler

The tire pressure on the manufacturer's sticker is likewise based on the size and type of tire and the GVWR. That should always be followed unless one is going over the GVWR it has changed the size or type of tire. They know what they are doing, in consultation with their tire suppliers and industry standards.


Land of 10,000 Lakes
2016 Forester MBS 2401R
Nights camped 2016: 32; RV to date: 35

Tires fitted to a RV trailer during the manufacturing process are done so in compliance with FMVSS standards. Those standards require the tires to have a load capacity equal to or greater than each individual axles' GAWR. Total GAWR is required to support the vehicle's GVWR.

Although RV trailer tires and automotive tires are fitted in accordance with essentially the identical standard there are provisions within the standard that causes the automotive tire fitments to differ from the RV trailer tire fitments. Those differences cause most of the confusion when talking about both fitments in a single forum thread.

[270S]

The door sticker psi is for THAT vehicle. Ride comfort is an input factor by vehicle manufacturers in addition to safety, life of tire, ....It is to be set at 100% ambient (cold) temperature. Refer to that vehicles manual if you are towing, ...

My 2008 GMC Sierra is set to 35PSI when I am just using it normally. Depending on how much I load up the truck bed, I will adjust the cold pressure up to 38-39PSI. When I approach full loading (towing TT) per tire and truck capacity, I use the full load rating of 41PSI.

The only complication (was another thread) is locations/altitudes that have wild temperature swings during the day/tip. This will take understanding everything said here and using informed judgement to adjust accordingly - there is no absolute correct answer to this scenario without knowing the science.

BTW, If I forget to lower it when I am done, the tires and ride will remind me.

[Airdale]

Originally Posted by 270S

The door sticker psi is for THAT vehicle. Ride comfort is an input factor by vehicle manufacturers in addition to safety, life of tire, ....It is to be set at 100% ambient (cold) temperature. Refer to that vehicles manual if you are towing, ...

My 2008 GMC Sierra is set to 35PSI when I am just using it normally. Depending on how much I load up the truck bed, I will adjust the cold pressure up to 38-39PSI. When I approach full loading (towing TT) per tire and truck capacity, I use the full load rating of 41PSI.

The only complication (was another thread) is locations/altitudes that have wild temperature swings during the day/tip. This will take understanding everything said here and using informed judgement to adjust accordingly - there is no absolute correct answer to this scenario without knowing the science.

BTW, If I forget to lower it when I am done, the tires and ride will remind me.

If it's not on the vehicle certification label (tire placard) or in the vehicle owner's manual you are improvising. Your method may be good for you but many others will disagree.

Vehicle manufacturers are pretty smart. They set the standards. Tire manufacturers give them the parameters to go by and the charts for the acceptable inflation pressures. They also follow the standards set by the vehicle manufacturers.
.

[270S]

Below are two actual pictures from my vehicle and tires documenting what I previously posted. No need for forcing opinions when science is available. the vehicle tires are to be inflated to 35 psi for comfort at apx 5200 pounds, 44psi when they are at loaded to their max capacity of 2205 pounds/tire. That would yield a truck weight of 8820#s, but with more weight on the rear vs front axle, I increase rear 2psi higher than front. My truck runs slightly heavy, so I keep it around 35/37#s for Front/Rear. With my truck at 6800#s during tow, vs my normal 5600#s, following is the apx setting:

5600 - 35 / 37psi
5900 - 36 / 38psi
6200 - 37 / 39psi
6500 - 38 / 40psi
6800 - 39 / 41psi
*************
7300 - 41 / 41psi
7800 - 42 / 42psi
8300 - 43 / 43psi
8800 - 44 / 44psi

[jadatis]

REaction to above 270S

Your tires are P tires in standard load , wich means that they are alowed to carry that 2205 lbs AT 35 psi up to 160km/99m/h.
Maximum speed of tire is S speedrated so 180km/114m?/h , and the difference between that 35 psi and the maximum allowed cold pressure of 44 psi/3bar, is used to highen up the AT 35psi pressure for higher speed, and camber angle.

This is the official system of TRA and ETRTO.
Standard Load =SL= AT pressure of 35 psi/2.4 bar in TRA system.
EURopean ETRTO system AT 2.5bar/36psi wich gives mostly 1 Loadindex step higher for the same sises SL tire. EUR system alows exeptions to lower ATf-pressure

XL/Extraload/reinforced P-tires AT 41psi/2.8bar in USA system, 2.9 bar/42 psi in EUR system also exeptions allowed .

So what the car maker did in its advice is giving AT-pressure so its never to low, and if you could determine the loads on seperate wheels 100% acurate , and your pressure device gave it 100% acurate, you could do with lower pressure . This 100% acuracy is never possible even if you weigh , and so you always have to go from as much possible reserve , and that is what the care maker goes from in its advice for reasons of responcability.
If only one goes over the GAWR's or drives faster then the advice is calculated for , the car-maker must pay nowadays.

[Rkloud9]

I have followed this and many other conversations about tire pressure, and, quite frankly, the posts in this thread are so "all over the map" that I cannot see how the OP could make any sense of it.

What is the justification for not using the tire pressure numbers recommended by the builder that are posted on the driver's door? My 2017 2400W (not much different than the OP's vehicle) rides and handles nicely using the suggested 61 psi on all 6 tires. We have driven about 14000 miles since April, and there is no uneven wear on any of the tires (we did have the alignment checked and adjusted after about 5000 miles.)

When we picked up the new motorhome from the dealer, they emphasized using these settings. On our first trip we drove on some less than perfect roads, and the ride was pretty harsh. We had a lot of difficulty checking pressures on the duals, as the extenders really did not work. Taking the truck to a tire shop, we found that all 4 were at 80 psi. Getting the pressure down to the recommended numbers made a real difference... it is still a truck, but tamer. We have since added a tpms, which provides a fair amount of peace of mind.

These MBS based motorhomes do not have a great deal of cargo carrying capacity (mine is about 970 lbs.). So, loading the vehicle to the max (11030 lbs) is less than 10% of the "off the line" weight plus fuel minus water (10060 lbs). Forest River has to assume that these motorhomes will be, at the least, fully loaded when we are all "out there". I know mine is.

I see no reason to overthink the 61 psi value... just be sure that is where they are, and you are good to go.


Bob & Cynthia
2017 SunSeeker MBS 2400W
Sent from my iPad using Forest River Forums

[Airdale]

Originally Posted by 270S

Below are two actual pictures from my vehicle and tires documenting what I previously posted. No need for forcing opinions when science is available. the vehicle tires are to be inflated to 35 psi for comfort at apx 5200 pounds, 44psi when they are at loaded to their max capacity of 2205 pounds/tire. That would yield a truck weight of 8820#s, but with more weight on the rear vs front axle, I increase rear 2psi higher than front. My truck runs slightly heavy, so I keep it around 35/37#s for Front/Rear. With my truck at 6800#s during tow, vs my normal 5600#s, following is the apx setting:

5600 - 35 / 37psi
5900 - 36 / 38psi
6200 - 37 / 39psi
6500 - 38 / 40psi
6800 - 39 / 41psi
*************
7300 - 41 / 41psi
7800 - 42 / 42psi
8300 - 43 / 43psi
8800 - 44 / 44psi

You say you're using the 245/70R17 tires on a pick-up truck. So here are some facts for you. Because the tire sizes depicted on your tire placard are Passenger tires they MUST be derated when being used on your truck. Their derated value is 2004# per tire at 35 PSI. At 44 PSI their load capacity is still 2004#. For SL tires there is no increase in load capacity from 35 - 44 PSI . Just a stiffer tire for the maximum load of 2004#.

Here is an excerpt from the FMVSS standard that requires the de-rating of passenger tires when used on other applicable vehicles.

S4.2.2.2 When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, the sum of the maximum load ratings of the tires fitted to an axle.

[SailorSam20500]

This guide from Goodyear gives a manufactures explanation of how much air. Goodyear's bottom line is, correct cold inflation pressure is dependent on how much the vehicle weighs, truck or trailer. So running tires at max inflation, when UNDER the max load weight the tire was designed for, should result in improper wear on the tire (excessive wear on center of tread).
http://www.goodyearrvtires.com/pdfs/tire-care-guide.pdf

With some research, you should be able to find the pressure numbers/weight numbers for your tires. To the OP's original question, the pressure listed on the trailer is for a specific trailer weight. I won't guess if that is the empty/dry weight or the max load weight for that trailer.

[Airdale]

Originally Posted by jadatis

REaction to above 270S

Your tires are P tires in standard load , wich means that they are alowed to carry that 2205 lbs AT 35 psi up to 160km/99m/h.
Maximum speed of tire is S speedrated so 180km/114m?/h , and the difference between that 35 psi and the maximum allowed cold pressure of 44 psi/3bar, is used to highen up the AT 35psi pressure for higher speed, and camber angle.

This is the official system of TRA and ETRTO.
Standard Load =SL= AT pressure of 35 psi/2.4 bar in TRA system.
EURopean ETRTO system AT 2.5bar/36psi wich gives mostly 1 Loadindex step higher for the same sises SL tire. EUR system alows exeptions to lower ATf-pressure

XL/Extraload/reinforced P-tires AT 41psi/2.8bar in USA system, 2.9 bar/42 psi in EUR system also exeptions allowed .

So what the car maker did in its advice is giving AT-pressure so its never to low, and if you could determine the loads on seperate wheels 100% acurate , and your pressure device gave it 100% acurate, you could do with lower pressure . This 100% acuracy is never possible even if you weigh , and so you always have to go from as much possible reserve , and that is what the care maker goes from in its advice for reasons of responcability.
If only one goes over the GAWR's or drives faster then the advice is calculated for , the car-maker must pay nowadays.

Our vehicles must be certified by the Department of Transportation (DOT). The National Highway Transportation Safety Administration (NHTSA) - an arm of DOT - writes and enforces safety regulations and standards. Federal Motor Vehicle Safety Standards are a set of regulations that all of our motor vehicle manufacturers and import manufacturers MUST comply with.

Here are a couple you should become familiar with before posting technical answers about tires and their fitments. They set the standard for all tire fitments. I know, there are others that work hand and glove with these two but these give the bare minimum standards for tire selections, fitments and recommended inflation pressures.

https://www.gpo.gov/fdsys/pkg/CFR-20...sec571-110.xml

https://www.gpo.gov/fdsys/pkg/CFR-20...sec571-120.xml

I see your posts about tires on lots of other forums. I use different names, you do not.

[OldCoot]

Originally Posted by FFred

The time to look at tire pressure is after a long hard run at speed.

Look at , just to see if the sidewall max tire pressure is surpassed.

Most tire mfg have a web site that will give initial cold tire pressures for specific tire loading. These take into account the pressure rise with highway travel.

FMCA and other folks can weigh the 4 wheels individually of your RV to find out if there is any overloading.

Sorry to disagree, but the time to check pressure is when the tires are cold.

[MNtraveler]

The OP request was about a F 2401R which is a motorhome, exactly what we have. The discussion should not be confused by information on pickup trucks and similar vehicles that have varying load conditions when used without load, with deck load or when towing. The motorhome is by and large a steady state environment and the manufacturer's recommendations should be followed. There is no reason to make it more complex than that. There should be no controversy.


Land of 10,000 Lakes
2016 Forester MBS 2401R
Nights camped 2016: 32; RV to date: 35

[MNtraveler]

Originally Posted by OldCoot

Sorry to disagree, but the time to check pressure is when the tires are cold.

Absolutely.


Land of 10,000 Lakes
2016 Forester MBS 2401R
Nights camped 2016: 32; RV to date: 35