Do I really need 80 psi in my rear tires?

[kmessinger]

My wife and my dog say riding in the back of the Travato is very bumpy and sometimes scary. I think it is because I have (as recommended) 80 psi in my tires that gives them a 5680 lbs. rating. I think I should be able use less psi because I am not near my GAWR - R of 5291.

However, I have been thinking about this for too long and my brain is now spaghetti.

How much air do you put in your tires?

Thanks,
Keith

tinyurl.com/y5xcwhcx

[Winterbagoal]

I usually run near the rated max cold inflation pressure. Better fuel economy on harder tires, and I don't notice much difference in the ride.
My wife doesn't seem to mind, and my cat never mentions it either.

[BobC]

1. The quick answer is "no", depending on your actual axle weights and the weight/pressure tables for your tires.

2. I respectfully disagree with Winterbagoal. The max cold psi on the sidewall of your tires is even higher than the recommended pressures on your door placard. I noticed a difference in ride, especially over bumps when I went the weight table route, reducing my PSIs below the door placard levels.

These two sites should give you everything you need to know. It seems complicated at first but is really pretty simple:

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

(Roger Marble is a retired tire engineer and Winnieowner)

https://www.goodyearrvtires.com/tire...n-loading.aspx

There are also many threads on this subject that you can read, the issues are not make/model specific.

[Morich]

I will say ---probably not and for a reason I had never thought of until I got a tire pressure monitor installed!
We know there are a number of things we often look at for pressure like weight but then we also read to set the tire pressure when cold. Cold being defined as not having been driven.
But what the tire pressure monitor giving me constant readings of the pressure has shown me is that the pressure I set is not going to be the pressure I drive on as it changes almost immediately after I start driving.

The tire pressure also changes depending on lots of other things like the direction the sun is shining and whether it is cloudy or not!

I find setting the pressure to a mid range is about all I can do as it is totally impractical to set a "cold" temp for Chicago and still expect it to be the right pressure when I get up a couple days later in Mississippi!

I refuse to start at the theoretical right pressure only to find it is way too high after I drive fifty miles so that I would need to let air out to have it right but need to add air back the next morning when they are too low!

Temperature, weather, road conditions and location of the tire on the RV will all change the pressure, so I now have stopped trying to get it "right" but just keep it in range for the season!

[akeagle]

Originally Posted by Morich

I will say ---probably not and for a reason I had never thought of until I got a tire pressure monitor installed!
We know there are a number of things we often look at for pressure like weight but then we also read to set the tire pressure when cold. Cold being defined as not having been driven.
But what the tire pressure monitor giving me constant readings of the pressure has shown me is that the pressure I set is not going to be the pressure I drive on as it changes almost immediately after I start driving.

The tire pressure also changes depending on lots of other things like the direction the sun is shining and whether it is cloudy or not!

I find setting the pressure to a mid range is about all I can do as it is totally impractical to set a "cold" temp for Chicago and still expect it to be the right pressure when I get up a couple days later in Mississippi!

I refuse to start at the theoretical right pressure only to find it is way too high after I drive fifty miles so that I would need to let air out to have it right but need to add air back the next morning when they are too low!

Temperature, weather, road conditions and location of the tire on the RV will all change the pressure, so I now have stopped trying to get it "right" but just keep it in range for the season!

I don't remember if Tireman ever addressed this or not, but given the high number of variables induced by altitude, ambient air temperatures, and vehicle weights it would seem logical that tire manufacturers must build a rather large "fudge factor" into their tires as far as air pressures are concerned. Using the "cold" pressure seems to be reasonable because there has to be a starting point for everyone. I think its completely logical to expect even new vehicle owners to use that benchmark as the basis to determine appropriate tire pressures.

The owners manual for my TPMS mentioned an expected 10 - 15% increase in pressure readings after the tires warm up, especially where the ambient air temp is already high. My observation of the TPMS display pretty much confirmed that. Even when we drove through NM and AZ in July in temps of 105 - 115 degrees I didn't see the tire pressures exceed that expected 15%
increase.

In hot weather the tire temperatures pretty much matched the ambient air temps with no ill effect.

So, that says to me there is something to that "fudge factor" theory. If the manufactures know exactly what that factor is, they don't appear to be publicizing it. Perhaps that could be for legal reasons because there would be those who would take that fudge factor as gospel and then sue when a tire failed.

[Winterbagoal]

I also do a visual inspection of the tires before we head out, and at almost all stops en route. If there's a noticeable bulge in the sidewalls, I'm probably running too soft, but since I do run at very near the full max cold inflation pressure, I rarely see that. To date, I have had no problems, and have always had excellent tire wear, and full rated longevity, as well.
To each, his own?

[BobC]

Originally Posted by akeagle

I don't remember if Tireman ever addressed this or not, but given the high number of variables induced by altitude, ambient air temperatures, and vehicle weights it would seem logical that tire manufacturers must build a rather large "fudge factor" into their tires as far as air pressures are concerned. Using the "cold" pressure seems to be reasonable because there has to be a starting point for everyone. I think its completely logical to expect even new vehicle owners to use that benchmark as the basis to determine appropriate tire pressures.

The owners manual for my TPMS mentioned an expected 10 - 15% increase in pressure readings after the tires warm up, especially where the ambient air temp is already high. My observation of the TPMS display pretty much confirmed that. Even when we drove through NM and AZ in July in temps of 105 - 115 degrees I didn't see the tire pressures exceed that expected 15%
increase.

In hot weather the tire temperatures pretty much matched the ambient air temps with no ill effect.

So, that says to me there is something to that "fudge factor" theory. If the manufactures know exactly what that factor is, they don't appear to be publicizing it. Perhaps that could be for legal reasons because there would be those who would take that fudge factor as gospel and then sue when a tire failed.

Tireman9 addresses this in several places in his blog. In general, he cites a 300% to 400% safety factor. Here's one such discussion along with some links to more:

https://www.rvtiresafety.net/2016/07...ssure.html?m=1

https://www.google.com/search?q=cold...hrome&ie=UTF-8

[misteracng]

Winnebago should have a recommended cold tire pressure label usually in the drivers door frame. On my view24D that is the cold pressure for a max load. In looking at the actually tire load inflation sheet from the tire manufacturer the pressure is enough to handle more than the GAWR for each axle, so they have given a bit of safety margin as well. I think no need to go more than that unless you are truly overloaded. It will just make the ride worse. You may actually be able to go down on pressure a bit if you weigh the coach.
There is no issue with running the max inflation pressure on the sidewall, maybe a bit more fuel economy and maybe harsher ride, but you might also have uneven wear. Keep in mind the tires will increase psi as you drive quite a bit which is already accounted for by the manufacturer. With my TPMS I see tire pressure can increase 6-10psi quite quickly and then stabilize. These RV's are heavy and cause more heat in the tires then normal cars.

[kmessinger]

From the Travato owners manual.
"If your actual weight is considerably less than
GAWR, you may be able to lower your tire
pressure. See a tire dealer for a load/pressure
chart."
The real question is why it took me 3 years to look in the owners manual?

[BobC]

Owners Manuals? We don't need no stinking Owners Manuals!

(apologies to John Huston and The Treasure of the Sierra Madre)

[Morich]

I feel it is always going to come down to a personal judgement factor. In my case, I drive where it is hot so much of the time, that I find I really prefer to set the "cold" pressure lower than recommended and find it often is much higher than recommended after I drive a bit. My cold tire pressure is often at temperatures well above 75, so if I set it the same as I did when living in Missouri, I would have a much harsher ride and I might assume a shorter tire life due to over inflation being the norm.

But my fall back position for getting the full use out of my RV tires is that I have never worn a set out as they tend to age out before they wear out, so I go for the better ride and what handles better and don't sweat the theoretical loss of wear.

[kmessinger]

[QUOTE=BobC;3886985]Owners Manuals? We don't need no stinking Owners Manuals!

Exactly!

[misteracng]

Originally Posted by kmessinger

My wife and my dog say riding in the back of the Travato is very bumpy and sometimes scary. I think it is because I have (as recommended) 80 psi in my tires that gives them a 5680 lbs. rating. I think I should be able use less psi because I am not near my GAWR - R of 5291.

However, I have been thinking about this for too long and my brain is now spaghetti.

How much air do you put in your tires?

Thanks,
Keith

tinyurl.com/y5xcwhcx

I'm curious, what is the winnebago recommended cold tire pressure for your travato, and what tires does it come with?

[Rick 99037]

You are right to think inflation is a formula of load VS air pressure to carry it. The ply rating then decides if you can put enough pressure in match the load.
Notice in the charts that with duals, you don't just divide the load by the number of tires. And of course they need to be within 5 pounds of each other, in a pair; so they are the right diameter, etc.
I suspect you measured per axle weight, and that's okay, but if you were a perfectionist, you could do each pair individually. In computing, remember water's about 8 pounds a gallon, gas 6 pounds, and diesel 7 pounds. So envision full tanks, and your supplies in the mix too.

Here's a Firestone tire, weight, and load chart. https://commercial.firestone.com/con...0Table%20A.pdf

[BobC]

Originally Posted by Rick 99037

You are right to think inflation is a formula of load VS air pressure to carry it. The ply rating then decides if you can put enough pressure in match the load.
Notice in the charts that with duals, you don't just divide the load by the number of tires. And of course they need to be within 5 pounds of each other, in a pair; so they are the right diameter, etc.
I suspect you measured per axle weight, and that's okay, but if you were a perfectionist, you could do each pair individually. In computing, remember water's about 8 pounds a gallon, gas 6 pounds, and diesel 7 pounds. So envision full tanks, and your supplies in the mix too.

Here's a Firestone tire, weight, and load chart. https://commercial.firestone.com/con...0Table%20A.pdf

My understanding is that all tires on an axle need to be at the same pressure, singles or duals. If you have four corner weights, the highest corner weight on each axle will determine the PSI for all tires on that axle.

[Beabop]

You need to weigh your rig, get the wt on your front and rear and go to the tire mfg chart. On our little C the front is 55 the back is 60.

Weight fully loaded for a trip including occupants before you weigh then you will know your correct wt.

[NeilV]

While you will often get better fuel economy when you use thee max cold pressure stated on the tires sidewall that will often result in accelerated wear in the center of the tire and reduced traction due to maintaining a smaller contact patch unless your vehicles load matches the max load rating of the tire. Best is to weigh the vehicle and inflate the tire to match the weight on each axle when fully loaded for travel. You do not deflate tires for a softer more comfortable ride unless that lower pressure actually matches what the tire chart says is required for the load you are carrying. You do not let air out when the tires warm up either as next time they cool they will be under inflated.

My father designed tires and rubber formulations for 47 years for everything from passenger cars/vans, racing, large aircraft, construction/farm equipment, off-road vehicles, heavy haul trucks, military vehicles, etc, etc. My uncles designed, manufactured and maintained tire production equipment.

[jcurtisis]

I just don’t understand why there are so many who don’t use the tire inflation pressure that the manufacturer recommends.

[dkoldman]

Originally Posted by jcurtisis

I just don’t understand why there are so many who don’t use the tire inflation pressure that the manufacturer recommends.

Why would a manufacturer recommend something in your best interest when it may impact their profits or expose liability. i.e. I was just about to by some valve extenders online when I just happened to read fine print from Mfg that said please do not use these extenders when vehicle is moving.

[Wyatt]

Originally Posted by dkoldman

Why would a manufacturer recommend something in your best interest when it may impact their profits or expose liability. i.e. I was just about to by some valve extenders online when I just happened to read fine print from Mfg that said please do not use these extenders when vehicle is moving.

Legal coverage. “Hey, We warned you”...

I have a box of fire starters that say, “DO NOT USE NEAR FIRE OR FLAME”.

Go figure.