Are your OEM tires the correct load rating?

[jerichorick]

I just had a email discussion with a irv2 friend about what load range tire is best for our coaches. Let me summarize what I learned using my coach as the poster child. There have been many threads on brands, sizing and psi values, but I have not seen actual load ratings discussed.

My rig has a GVWR of 32,350#. The front is rated at 12,350# and the rear is 20,000#. My coach weighs in as follows: Front left 6,050#, Front right 6,200#, totaling 12,250# of load. The rear: Left 10,750#, Right 10,950#, totaling 21,700# and a total coach weight of 33,950#. Yes, I am overweight by 1,600# as of that weighing. But this is NOT about coach weight directly. I am focusing on the tire load ratings here.

My OEM tires are the Michelin XZE2 275/80R22.5 with a load rating of 2,800# single and 2,575# duel wheel. Right out of the factory door this coach was riding on unsafe, overloaded tires! I have compounded the problem by being 1,600# overweight. This was not seen as a problem by Freightliner in Gaffney, SC.

Because the 275/80 is only produced by Michelin (as far as I can tell) for the RV industry, it is a hard size to get in a hurry. Many of us are going to the 295/75 size for our rigs as a good, readily available, replacement.

I am looking at the TOYO M154 295/75R22.5 to replace my rear tires. For a single axle this tire is rated at 6,610# and for the duel, 6,005#. This is a much better tire for this coach weight. Another good reason for changing brands is the sidewall cracking issue of the Michelin's and the $$$ compared to other comparable brands.

Now to the cold psi of the tires. The XZE2 is maxed at 110psi. The M154 is maxed at 120psi. Obviously my coach has been running at max psi. My cold psi won't change with the new tires but the load for the psi I am using is not maxed out for this tire either.

Happy trails and safe trails to all. The best part of RVing is getting there safely.

Rick Y

[Mr_D]

The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From page 2 of the 06/07 Michelin RV Tire Guide:

"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."

From page 6 of the GoodYear RV Tire and Care Guide:

"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

From TOYO:

Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.

But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:

The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.

[Mr_D]

According to the Michelin book I have in front of the me the XZE2 275/80R22.5 max weight rating of 6175 @ 110 psi (12,350 total axle, 6,175 each side) in single use, in dual use it's 5675@110 psi (22,700 total axle, 11,350 each side).

[LVRVLUVR]

Originally Posted by Mr_D

According to the Michelin book I have in front of the me the XZE2 275/80R22.5 max weight rating of 6175 @ 110 psi (12,350 total axle, 6,175 each side) in single use, in dual use it's 5675@110 psi (22,700 total axle, 11,350 each side).

I'm gonna say that they set the gvw at the tire rating on his coach..,...

[LVRVLUVR]

Originally Posted by jerichorick

I just had a email discussion with a irv2 friend about what load range tire is best for our coaches. Let me summarize what I learned using my coach as the poster child. There have been many threads on brands, sizing and psi values, but I have not seen actual load ratings discussed.

My rig has a GVWR of 32,350#. The front is rated at 12,350# and the rear is 20,000#. My coach weighs in as follows: Front left 6,050#, Front right 6,200#, totaling 12,250# of load. The rear: Left 10,750#, Right 10,950#, totaling 21,700# and a total coach weight of 33,950#. Yes, I am overweight by 1,600# as of that weighing. But this is NOT about coach weight directly. I am focusing on the tire load ratings here.

My OEM tires are the Michelin XZE2 275/80R22.5 with a load rating of 2,800# single and 2,575# duel wheel. Right out of the factory door this coach was riding on unsafe, overloaded tires! I have compounded the problem by being 1,600# overweight. This was not seen as a problem by Freightliner in Gaffney, SC.

Because the 275/80 is only produced by Michelin (as far as I can tell) for the RV industry, it is a hard size to get in a hurry. Many of us are going to the 295/75 size for our rigs as a good, readily available, replacement.

I am looking at the TOYO M154 295/75R22.5 to replace my rear tires. For a single axle this tire is rated at 6,610# and for the duel, 6,005#. This is a much better tire for this coach weight. Another good reason for changing brands is the sidewall cracking issue of the Michelin's and the $$$ compared to other comparable brands.

Now to the cold psi of the tires. The XZE2 is maxed at 110psi. The M154 is maxed at 120psi. Obviously my coach has been running at max psi. My cold psi won't change with the new tires but the load for the psi I am using is not maxed out for this tire either.

Happy trails and safe trails to all. The best part of RVing is getting there safely.

Rick Y

did you ever weigh front and rear axels?

[jerichorick]

Originally Posted by Mr_D

According to the Michelin book I have in front of the me the XZE2 275/80R22.5 max weight rating of 6175 @ 110 psi (12,350 total axle, 6,175 each side) in single use, in dual use it's 5675@110 psi (22,700 total axle, 11,350 each side).

WoW! Are my eyes bad. I read the Kg. Sorry.

Rick Y

[jerichorick]

Originally Posted by LVRVLUVR

did you ever weigh front and rear axels?

Done this twice and 4 corners. Once when the coach was new to us, in Gaffney, SC at Freightliner and last year at Henderson's in Grants Pass, OR.

[jerichorick]

Mr. D, we seem to be going round and round on this one. The way the tech is expressing the issue is under the assumption, I have to believe, you are referring to cold psi values. It only makes sense that the 110psi cold is the minimum pressure to be used for the maximum load rating of the tire. On the manufacture's charts they give appropriate cold psi values for lesser loads in psi values lee than the max. See the sidewall of my tire:

[AFChap]

It does make a difference reading kg vs lb! I replaced 2 of my original Michelin 275/80R22.5 LRH - (XZA2) tires with Continental HSLs in the same size & load range designation when I could not find an XZA2 that had a defect at 5 yrs. Michelin gave me an adjustment on the tire. I had no complaints about the Michelins & never saw any cracking. The XZA2s had more capacity than the axles (12k & 20k), and the Continentals do too. I have since bought more Continentals because the ride & handle very well & are cheaper than the Michelins.

[l1v3fr33ord1]

Rick-

I don't know if you can actually buy them, but Michelin charts show a 275/80R22.5 (load range H) in both the XZA3 and XZE products. Both are the within 0.1 inch of the same diameter as the load range G XZE2s you have now, and have max load/pressures of 7160lb@120psi (single) and 13220@120psi (dual). I'm curious as to why these tires aren't on your radar as replacements for the XZE2s.

[jerichorick]

Originally Posted by l1v3fr33ord1

Rick-

I don't know if you can actually buy them, but Michelin charts show a 275/80R22.5 (load range H) in both the XZA3 and XZE products. Both are the within 0.1 inch of the same diameter as the load range G XZE2s you have now, and have max load/pressures of 7160lb@120psi (single) and 13220@120psi (dual). I'm curious as to why these tires aren't on your radar as replacements for the XZE2s.

I could, but I don't want Michelin. They came on the 3 coaches I have owned and all had sidewall checking before I replaced them. For much less money I can get as good or even a better tire in another brand. I have Continental's on the front but they were more $ than I was planning to pay. Long story. Toyo is a good tire and I had them as replacements on my first coach. Didn't have it long enough for a long term evaluation but they rode very well.

Putting tires on a rig that are at max load rating, especially on the front, seems to be pushing the safety envelope a bit too much IMO. H range should be the minimum for a 40' coach with all the basement available this one has, and the GVWR of 32,350. It is too easy to overload and not realize it till you get to a scale. Not everyone is quick to get weighed. I fall into this category I must confess. Some folks worry about the axle load ratings. It is rare that you see of hear of an axle failure do to our type of common overloading. Tire failure is very common. Many factors can bring this on. I am certain overloading is in the mix.

The max load rating is spected by a minimum cold psi rating. If you go over the psi rating of the tire you still have a tire that is designed for a max load but now able to carry more weight as in the next range up. But, is this wise or safe? NO, because the tire is not designed to carry a larger load even though you have added 5, 10 or... psi more. With more air at or below the load limit of the tire, it simply stiffens the ride and can wear the tire in a strange way.

A friend on the forum and I are in conversation about this topic. He is leaning toward the Toyo M177 tire or the Continental HS3 as I have on the front. Either is good choice and less money than the Michelin. Both are available in the H range. We will both pull the trigger soon.

Rick Y