The sticker on my u320 states the inflation on the steer tires should be 115 psi, but the max pressure on my new tires are 110psi.
They have a G load rating, did I get the correct tires?
I know I should really get the coach weighed and base the inflation off that, but for now I'm just trying to get in the ball park.
Thanks
Steve & Shaye
What brand and size tire?
We have Goodyear Endurance LHS - 297/75R22.5 load range G on the steer and tag axles. Traction tires are installed on the drive axle (Goodyear Endurance LHD - 297/75R22.5 load range G)
Inflate to the tire not the sticker. 5 psi is not going to make any difference.
Pierce
As you go on to state, the PSI on the GVWR sticker is correct pressure ASSUMING each axle is loaded to its GAWR.
As far as correct tires, go to the tire manufacturer's website and verify that the tires meet the GAWR's of your coach/actual weight, which ever is higher. And, I would sure want at least a 10% safety cushion/not have tires loaded to 100% of their rated capacity.
Looks like you LHS LR G tires are 6175lbs at 110 psi. So the only way to know is to have the coach weighed. With a 38' tag you at likely fine.
X2...........I'm a big believer in four corner weighing, especially if a newer tire size is installed. When our Michelins were installed, someone just took the specs for the OEM size and pumped them to 110 psi. The coach rode like hell. I had it 'four cornered' and found that 85 psi was where I wanted to be. Sweet ride now! ^.^d
I bought the tag so I have the option of installing a hyra-lift and ~750lbs of motorcycles off the back. No point weighing the coach until I do that, but I'm holding off until I'm sure it's worth it (could be a year).
I should have put more thought into the tires, but it was a hasty decision made on our way to Nac. I didn't feel comfortable the tires that were sold with the coach would make it. They were 8 years old and the sidewall cracks were getting worse during the trip.
Your front axle weight will go down when you mount that, an even more when you load it.
I'm sure you'll be fine weight wise. When you head out for trip just run the coach I've the scale at most any truck stop. You will have piece of mind.
Yup, I was more concerned about exceeding the ratings on the drive/tag axles.
Since I have no first hand information setting up tag axle Foretravels, a question:
Is tag axle ride height/load adjustable? If so, how?
Ideally, each axle will be loaded to the same PERCENT of its GAWR.
At several of the Diesel RV Club Rallies when I was President, all wheel position weighing was the "rally gift". With some tag coaches (thinking of Monaco in particular) adjusting load on the tag was super easy. Not a single tag axle coach we weighed was close to the same percent of GAWR on each axle. We would adjust and run them around to weight again until we got it right (lot of swag involved, as changing load on tag changes both drive and steer axle weights). Got several phone calls the afternoon everyone left the rally-- " my coach has never driven this well". We found most tags WAY underloaded, which left the front axle underloaded and drive axle overloaded.
We had Load range G tires on our 2001 U320 when we bought it. 110 psi max. They were far from enough to meet the GAWR for the front axle and when we had it weighed we were close to the max for those tires. The front axle weight rating is 13,880 pounds as I recall. We were well under that but switched to Load Range H which for the tires we bought at 120 psi were good for 14,320 lbs. plenty of wiggle room now. And I think the LRH tires handle better.
The only way to know for sure is to get it weighed, preferably all four corners. And then after a couple years of actual use do it again. Most of us start hauling around more stuff because there is room for it.
On the 40 footer anyway, no adjustment possible. Axles are 13880 front, 21000 drive, and 9000 tag.
I run 12640 steer, 17000 drive and 7700 tag. I have a lot of tile and granite so the OP's 38 footer is probably a lot lighter.
Also went to 295 H on the front.
Jim,
So, what determines PSI to the tag air bags-- reducer off drive axle? Separate ride height valve? Other?
From the air schematic, appears same air pressure from the drive axle HCV's, is sent to tag bags as well. Tag bags may be a different profile, so less weight is transferred to tag.
Load Range G may be ok, but we only buy Load Range H.
Our coaches are all over 30,000 and our tires can use all the extra safety capacity afforded, especially when a tire is temporarily not at its optimum PSI due to cold weather, higher altitude, turning side-to-side loading, etc.
Weighing coach gives us a static reading that changes in real world driving down the road.
Barry is quite correct in that load range G does not handle as much weight as H. The construction may be slightly stiffer so could give a little more firm ride. Also, ply rating does not mean it has more plies as this was figured when the tire cords were made out of cotton. Now the ratings are just heavier construction that will handle more weight and speed. While we could send the same car to the U.S. with T or H ratings, the speed potential of most of our cars required that they have V rated tires when mounted in Germany. The difference in weight was at least a kilo or two, enough to instantly notice when picking one up.
Static weights are only that and why I never have weighted the coach. In the real world, changes in the diesel in the tank, propane, waste water, fresh water, amount of provisions all can have quite a bit of difference in weight day to day. Since the propane tank and fuel tank are off center on many coaches, the left to right balance will also change along with the tire on the diagonal as fuel and propane are used.
Pierce
When they do a four corner weigh at Escapees or by RV Safety they want a normal load of stuff, driver and pass, full fuel, full water, empty waste. Pretty typical upper end load for you. If you have less water, less fuel, less propane later on ... OK. Not knowing what your coach weighs just means you are guessing at several important safety concerns.
Wheel Position Weighing (https://rvsafety.com/weighing/wheel-position-weighing)
SmartWeigh ยท Escapees RV Club (https://www.escapees.com/education/smartweigh/)
G Michelin's are 6710 h are 7160.
I used that ratings to put h on our coach and drop the air to 97 front and 87 rear for better ride on so cal freeways.
Worked well with Koni FSD'S
Really well.
Speaking only for myself, I run only H rated tires on large Class A motorhomes.
And I especially want H rated on the steer axle of a tag axle coach (it bears the most weight per tire on the steer axle)
The air pressure may be the same for drive and tag but, the drive axle has 4 air bags the tag has 1 bag on each trailing arm.
On the Entregra forum there was a discussion on weight balance between the front, drive & tag and how it changes based on PSI to the tag bags. There was someone that put a pressure regulator for the tag so he could change the tag pressures and he did a number of test as to what the pressure change did and how it changed the load on each tire. I
You might want to do a google search on your Goodyear tires. I know their have been a lot of discussions on other forums about Goodyear tires blowing out on Coaches that come with them new. Not sure you have the same or different one.
Monaco also uses an easily adjustable pressure regulator to control PSI to the tag.
Of course, a separate ride height valve for the tag axle could achieve the same thing, but there can be some down sides.
What do you think Brett?
Don't see any adjustment. Would have to put a pressure regulator in lines 80 and 81. WAY past my pay grade to know all the pluses and minuses.
James Triana at Foretravel or Aubrey Lee at MOT would be the best people to work with on any project like this.
BUT, only worth it if percent of GAWR is way off between the three axles.
Yes, Aubrey has already told me the system was designed so no adjustment was possible or necessary.
Curious me-- I would still confirm that you have close to the same percent of GAWR on each axle before concluding that "no adjustment is necessary".
SO, any tag axle owners who will share this info:
Front axle GAWR Front axle actual weight Actual weight as percent of GAWR
Rear axle GAWR Rear axle actual weight "
Tag axle GAWR Tag axle actual weight "
I am running about 90% gawr front, 85% drive, and 80% tag. If I put a 1500 lb motorcycle and lift on the back, would tag take most of weight, or would it be distributed between tag and drive?
If I recall the tag axle has a single air bag on each side and the drive axle has two air bags on each side. Assuming you are on level ground and all of the air bags are the same and at equal pressure and that the geometry of the tag axle puts the tires in uniform contact with the ground as the drive axle.
Think this through...
It would look like three legged stool at each end of the rear axle pair. Wouldn't the drive axle carry twice the load that the tag carries? And since the drive axle has two tires on each end and the tag only one wouldn't all three tires individually carry the same load? And if so they should all be inflated to the same PSI?
I don't have a tag and have not seen weight measurements from one. Just trying to think it out.
Without raising the tag pressure it would get the brunt of the added weight. Just physics.
Jim C. (jcus) posted a formula a few years ago, that may help the discussion.
Current Camper Until FT Purchase - Can it Be Toted? (https://www.foreforums.com/index.php?topic=28572.msg259070#msg259070)
I am going to guess the tag is going to take the brunt of the weight. Remember weight to back takes off the front, tag down force puts weight back on front. Now add ride height contol and we have all kinds of unknowns
Good point, forgot about that, but now instead of a "teeter totter" effect with a single axle, you now have two axles designed to take equal [for their axle rating] loads. Be a shame, welding on your $5000 Hydralift, loading up your full dresser and finding out your axles are overloaded.