Request: tire pressure recommendations

[treejay]

1994 Chinook Concourse (diesel E-350, 7.3L IDI)
Tires: Yokohama A/T G015
Tire size: LT225/75R16

Weighed axles this evening, full gass tank, full water tank, half propane tank, generally fully loaded.
front axle: 3440 lb
rear axle: 6720 lb

What would you inflate your tires to if you had these specs? And why?
Thanks in advance for your recs!

[caconcourse]

Our tires are generally E-rated, and probably have similar load ratings across brands.

Here is a good discussion on MIchelin, including some weight charts:
http://www.dmbruss.com/images/FullTimin ... ochure.pdf

Here is a sample load chart for TOYO:
http://www.dmbruss.com/images/FullTimin ... tables.pdf

For your axle weights, front should support about 1720 per axle end (1/2 axle weight) and rear about 3360 per axle end.
The TOYO chart recommends about 50lb for both the single front and dual rear for that weight.
The Michelin XPS RIB chart would indicate 45lb for front and 50lb for rear.

This would give you a ballpark estimate and would suggest 50lb all around would be safe and comfortable. Personally, I set mine to about 55lb all around, to provide some margin, and am happy with the ride.

[markatherton]

If you go to the tire manufacturers website you should be able to see charts for weight/tire inflation; I believe you will find 45-50 is correct. I got this tip from "Blue"

[chin_k]

Blue who? Just kidding.

The kids at the tire shop keep putting 80 psi on the rear tires, and I have to keep telling them it is a dually, and have different pressure recommendation. After a few times, I just bleed off the air myself.

I would go with the sticker on the driver door as a starting point, and use the manufacturer table for minor adjustment based on loading.

[Blue~Go]

Blue who?

Hey, hey!

Too funny though as I have not visited the forum in a long time and look what's in "new posts" the day I come back

I would go with the sticker on the driver door as a starting point, and use the manufacturer table for minor adjustment based on loading.

Clay has it right. Go on the tire/weight charts. Because here's the thing: Ford puts that sticker on the door when they build the chassis cab. They have no idea what's going to happen after that so they are just making some guesses. We, on the other hand, have our finished Chinooks, loaded exactly as we have them loaded. So we can weigh the actual axles and inflate to the correct pressure for that weight. We don't need to use Ford's guess that they made before Chinook even had the bare chassis cab.

I think my Concourse with 80psi would ride like popcorn in a popper. Ugh. My buddy's fully loaded 27' E-450 motorhome did weight enough to need 80psi in the rear, but that was a big beast.

BTW I have those Yokohama G015 tires on my car and love them. Basically I wanted the most "on roady" off-road tire possible for that vehicle and that's how they seem. (Still running Michelins on the Chinook though, but the G015 might be sweet.)

[NUUKEEE]

Hey all,

TIRE PRESSURE: Agree with Blue-Go.
Go with tire pressure ratings on the tire.
Had an alignment done at an Alignment Shop recently because there was a slight pull to the right (since I bought "The Nook" in July 2021). I was a bit taken aback when I took the RV home and had a good look at things. The shop had inflated the front tire pressure to 80 PSI on both sides.
So a quick call to the Alignment Shop got me a quick explanation (and a little SCHOOLONG). The tires that are on this Chinook (Cooper) are rated for a max cold fill PSI of 80. Ford door jam sticker shows fronts to run at 65 PSI and rears to run at 55 PSI. The shop said the profile of the tire at 80 PSI will give an even wear (all alignment things being correct) and that if the ride is too stiff, I shoulda, coulda, woulda play with (decrease) the pressure till I am happy ... but again, I need to be clear that the profile of the tire at lower (softer) pressure would likely wear the shoulders of the tire faster than the center tread.

TIRE ROTATION: Not to further confuse anyone (including myself) but, I've got a tire rotation question. While reading the Ford Manual, I see that it calls for only rotating the front tires. To me, that means we leave the rear tires in the rear where they were positioned when initially installed. In other words, Do Not Rotate the rear dual tires.
This is different from every car or light truck I've owned in the past 51 years.

WOW. So, what say you ??

Cheers

N~

**** UPDATE 2022-02-10 ****

Please disregard my statement in the earlier post on this thread: "Go with tire pressure ratings on the tire."

Wow - Am I ever getting SCHOOLED - in a variety of ways but gotta say - this forum is very cool and super helpful on many levels. Who knew that there could be so many opinions, experiences and calculations for TIRE PRESSURE ... Right !! After reading the additional entries on this thread, doing some random searches on the internet and contacting the mfg. of my tires, Cooper Tire , I have a better appreciation for tires, tire pressure and what tire pressure means to RV handling and safety.

To Blue-Go: Thanks for being quick (and kindly) responding to my post. Your post got me to realize I did NOT really understand what I was reading. I did however start all this with the feeling that the Alignment shop inflating my tires to 80 psi was not right. Fortunately, I follow my gut on such things and that lead me to a new understanding.

Here is where things stand for me now:

My 1999 Chinook Concourse (Trail Wagon) Tire Placard states recommended tire pressure : 65 psi front and 55 psi rear.
My Tires: Cooper - Discoverer HTP LT225/75 R16, Load Rating E, Max Cold Inflation Pressure 80 psi.

Vehicle Placard: RV Mfg companies are required to put a placard on the vehicle with the tire size and pressure ratings (along with some other stuff). So I went out to the Chinook at 10:25 pm last night and sure enough, Trail Wagon had a (HARD TO READ) sticker on the door. Originally, I looked only at the FORD sticker and assumed that it was probably not correct because Ford had delivered the E-350 "Cutaway" to the RV Mfg and would not know what (weight) would be put on the the truck frame, but it turns out the the Ford and the Trail Wagon placards show the same PRESSURE figures.

Cooper Tire: I called Cooper Tire and the rep pulled up their charts. She said that according to the chart they use, the front tires would be set at 40 psi and the rears a little less. At that point she stopped the discussion and said very clearly, USE the pressures on the RV mfg's placard. Considering Ford and Trail Wagon both call out the same tire inflation numbers, that's where I will return my tire pressures at this point.

=======================

The following information was copied from the web site: https://vehq.com/rv-tire-pressure/ and presented here as information only.

What Happens if Your RV Tire Pressure is Too High or Too Low?
Driving your motorhome or towing your travel trailer or 5th wheel with the wrong level of tire pressure can lead to all sorts of problems, affecting your stability, ease of ride and even gas mileage.

When RV Tire Pressure is Too High
The over-inflation of tires makes the sidewalls and tread of the tire harder than normal. This can limit the performance and traction of the tire. Also, it may cause uneven tire wear. Plus, over-inflation will lead to a harsh ride, wobbly handling in the wind, and reduced braking effectiveness that is especially reduced on wet roads. If you're towing a travel trailer, it could also lead to sway issues. Read more on how to prevent travel trailer sway in this post (see https://vehq.com/rv-tire-pressure/ ). Also, tire pressure that is too high can cause a slight increase in gas mileage by reducing the rolling resistance of your tires.

When RV Tire Pressure is Too Low
Most tire blowouts are caused by underinflation. Underinflation will force tires to come into contact with the ground more than properly inflated tires would. Read more on RV tire blowouts (and how to prevent them) in this post.

To be more specific, the sides, or shoulders, of tires flex more when under-inflated which produces an excessive amount of heat, and excessive amounts of heat lead to tire failure.

If your tires are under-inflated by just 10 or 15 psi, then the temperatures on the sides of the tires can reach 200 degrees Fahrenheit.

Is High or Low Tire Pressure More Dangerous?
There is a simple answer to this. Low tire pressure is more dangerous than high tire pressure.

Low tire pressure leads to dangerous blowouts while high tire pressure is generally less dangerous. This is true as long as the tire pressure is below the "maximum inflation pressure." If you go over that, you could end up with a blowout as well. Of course, there are other safety issues associated with high tire pressure, such as increased sway when towing.

=======================

Final Thought:
This has been a learning opportunity for me ... and caused me to think differently about tires.

[68camaro]

I air my chinook to doors sticker recommendations. I really think I will be changing out tires due to age before wear becomes an issue. Also, I do notice at higher than air levels rig drives rougher.

[Blue~Go]

Hey all,

TIRE PRESSURE: Agree with Blue-Go.
Go with tire pressure ratings on the tire.

I think we actually aren't agreeing here. What I am saying is weigh your rig (which I think everyone should anyway). Once you have a front axle weight and a rear axle weight, plus the inflation chart for your tires (or at least for same size similar tires), then you read across and down and find your proper inflation.

I can pretty much guarantee it is NEVER going to be 80psi on a 21' Chinook. Why do I say that? Have a look here:

Okay, now for a couple of examples.

1) Let's work "backwards" on the chart for the rear axle. Four of these (stock size) tires at 80psi would be good for 2,470# per tire on a dually setup. That's 9,880#. But our rear axle is only rated (by Ford) to 7,500# MAX (or possibly 7,200 for some older E-350's). So you are either running *majorly* overweight on your rear axle, or your tires are very, very overinflated (reducing contact patch and harshening ride).

2) Let's do the same on the front axle. 80 psi (looking at chart) is good for 2,680# on a single setup (front axle). So that's the correct inflation for the front axle at 5,360#. But our front axle is only rated (by Ford) to 3,700#. So unless you are running the front axle at nearly 50% over its rating, the tires are overinflated. Boo.

Now let's go the opposite way. Let's say you have both the front and rear axle absolutely maxed out on weight. So 3,700# front axle; 7,500# rear axle.

Front axle weight at full rating divided by 2 (two tires on that axle) is 1,850#. Looking on the inflation chart for a single that would be a recommended psi of about 47#. Not 80.

Rear axle weight at full rating divided by 4 (four tires on that axle) is 1,875# per tire. Looking at dually line on chart that would be a recommended 55# of inflation. Not 80.

This doesn't mean you can't adjust them slightly if you want, but I can't see any scenario where 80# would be anything but very wrong. And this is for absolute MAX weight rating on our axles.

(Inflation chart for a larger tire would probably have you at a lower psi, but you can look at an actual chart and see).

The shop said the profile of the tire at 80 PSI will give an even wear (all alignment things being correct) and that if the ride is too stiff, I shoulda, coulda, woulda play with (decrease) the pressure till I am happy ...

IMO people who tell you to put them to 80 and then "adjust" either don't undestand how inflation charts work -- or think you won't understand and dont want to be bothered by details. Or maybe think they know more than Michelin et al? And hey, 80 psi is printed on the tire so there you go

[Blue~Go]

On the rotation:

I have never rotated my rear tires. Not because I knew I wasn't supposed to. I've never looked into it because I have extended valve stems (the all-metal shaped ones) and thus cannot rotate in the usual pattern. I can say that having just replaced my rear tires (due to age), there was nothing at all on the tread to indicate wear that was caused by needing rotation (this was after about 50,000 miles). I have a feeling the duallys may not wear that way? I mean they are kind of in lockstep with each other. What has anyone else found?

I have rotated my front tires side-to-side, and I believe that is permissable. I have extended stems on those too but they are interchangeable left to right.

[ltg]

Has anyone ever heard the saying you can take a horse to water but you cannot make it drink the water.
Well, this applies to tire pressures.
What Blue has said about tire pressures, adjust them to the weight they are carrying per the tire manufactures charts has been the standard for years and years and years.
If anyone thinks different, RV owners, tire dealers, tire shops, alignment shops, etc. let them think that way. Thats OK.
Just don't pay any attention to them.
Weigh your coach. Get the tire charts. Adjust your tires air pressures.