Tire capacity question

[rhagfo]

Originally Posted by CWtheMan

I doubt you read about tires more than I do. In the 2010 tire rules committee meeting The Laod Range Lettering system was confirmed to be the official rule for LT and ST tires.

There are no LT or ST tires with the designation 235/80R17. The "E" after a tire size designation with prefix ST or LT is the load range letter for that tire. You just cannot have a pick and choose maximum load capacity rating. The load range letter for that tire has a maximum load capacity of 3042# at 80 PSI. Double standards are not acceptable.

Read the information on the tire sidewall. It will tell you what the PSI rating is for that tire and the amount of load capacity it will support.

I found one in a Toyo load inflation chart.
LT235/80R17 Single 1725 1895 2055 2270 2370 2515 2680 2805 2940 3085 (E) 120

In written information about tires, the size is normally referred to as size. However, all of our tires are identified by designated size. So, when getting specific the whole designated size must be identified.

These are the most commonly used tire designated size prefix.

P-Metric
• Metric (a.k.a. Euro-Metric)*
• LT-Metric
• LT High Flotation
• LT Numeric
• European Commercial Metric (C-Type)*
• ST Special Tire for Trailers
• T-Type Temporary Spare

* Metric tires do not have an alpha character prefix in the size designation.

Make sure you're using the proper load inflation chart.

Maybe you should go to a tire site like Discount Tire, and ask for tires for any Ram 3500 DRW for the last 20 years. They all use LT235/80-17 E tires.

[CWtheMan]

Originally Posted by rhagfo

Well with a SRW running at or near Max pressure makes sense, although I ran the LT265/70-16 on our 2001 Ram 2500 at 75 psi, as I didn't need all the capacity, even that was a bit high for the axle weight.

Now as with OP and myself with a DRW, the LT235/80-17 has a dual capacity of 2,835# ea. at 80 psi. That is a total of 11,340#. Loaded I carry about 7,200# on the rear axle, this is about what the OP would carry. That is an excessive capacity of 4,140# making the tires overinflated for the load, and reducing traction. My rear axle is rated at 9,750# at a tire inflation of 65 psi ( this is from the tire inflation/payload sticker!). I run at about 55 psi as I am still 2,550# less than the axle rating.

I had a neighbor who ran log trucks, ran his tires at 10 or 20 psi less than max inflation, Why? when running at max the logging road rock was cutting the the tread terribly and loosing chunks. At the lower pressure far fewer cuts and no blowouts, or tread loss.

What is the GAWR for your axles?

The FMCSA standard is to ensure all tires are inflated to a PSI value that will support the load on the axle. Using less is a safety violation. Enforcement is done by state DOT officers at all weight stations at all weight stations.

If lowering those tires was in accordance with off road low speed conditions supported by a supplemental tire placard, they would have to meet the highway standards before operating there again.

[rhagfo]

Originally Posted by CWtheMan

What is the GAWR for your axles?

The FMCSA standard is to ensure all tires are inflated to a PSI value that will support the load on the axle. Using less is a safety violation. Enforcement is done by state DOT officers at all weight stations at all weight stations.

If lowering those tires was in accordance with off road low speed conditions supported by a supplemental tire placard, they would have to meet the highway standards before operating there again.

Do you read the entire post before replying??
My rear axle rating is stated in my post! It is, in the post.

[sourdough]

Originally Posted by rhagfo

Well with a SRW running at or near Max pressure makes sense, although I ran the LT265/70-16 on our 2001 Ram 2500 at 75 psi, as I didn't need all the capacity, even that was a bit high for the axle weight.

Now as with OP and myself with a DRW, the LT235/80-17 has a dual capacity of 2,835# ea. at 80 psi. That is a total of 11,340#. Loaded I carry about 7,200# on the rear axle, this is about what the OP would carry. That is an excessive capacity of 4,140# making the tires overinflated for the load, and reducing traction. My rear axle is rated at 9,750# at a tire inflation of 65 psi ( this is from the tire inflation/payload sticker!). I run at about 55 psi as I am still 2,550# less than the axle rating.

I had a neighbor who ran log trucks, ran his tires at 10 or 20 psi less than max inflation, Why? when running at max the logging road rock was cutting the the tread terribly and loosing chunks. At the lower pressure far fewer cuts and no blowouts, or tread loss.

Bouncing through threads I actually forgot that the OP had mentioned DRW. I would still ask what the placard calls for on a DRW? I wouldn't think it called for 80psi like a SRW. For the reason mentioned above I would pay attention to that.

I've had personal vehicles, and some of my company vehicles, lose rubber because they were overinflated for the load; one that comes to mind is Firestone Transforce AT at 80psi on an empty HD truck. That rubber chunking has a lot to do with the tire itself and how it is constructed, rubber compound etc.

[rhagfo]

Originally Posted by sourdough

Bouncing through threads I actually forgot that the OP had mentioned DRW. I would still ask what the placard calls for on a DRW? I wouldn't think it called for 80psi like a SRW. For the reason mentioned above I would pay attention to that.

I've had personal vehicles, and some of my company vehicles, lose rubber because they were overinflated for the load; one that comes to mind is Firestone Transforce AT at 80psi on an empty HD truck. That rubber chunking has a lot to do with the tire itself and how it is constructed, rubber compound etc.

I mentioned it in my post, but somewhat buried. The payload placard states 65 psi for the LT235/80-17 E tires.

[CWtheMan]

Originally Posted by rhagfo

Do you read the entire post before replying??
My rear axle rating is stated in my post! It is, in the post.

So, your federal certification label displays a rear axle GAWR of 9750? That's very high for a vehicle with a 14,000# GVWR. What does the axle manufacturer's weight tag list?

[JRTJH]

Originally Posted by CWtheMan

So, your federal certification label displays a rear axle GAWR of 9750? That's very high for a vehicle with a 14,000# GVWR. What does the axle manufacturer's weight tag list?

Cal,

A RAWR in the 9750 range is not "very high". In fact the 2016 Ford F350 DRW has a 13,000 GVWR and the rear axle rating is 9650.

In later year models, the GVWR is 14K and the RAWR is 9750 for the chassis cab configuration (essentially no pickup bed from the factory, but there are other changes as well).

At any rate, having a 14K GVWR and a RAWR above 9500 pounds is not "very high" but rather it's the norm for modern DRW pickup trucks.

[CWtheMan]

Originally Posted by JRTJH

Cal,

A RAWR in the 9750 range is not "very high". In fact the 2016 Ford F350 DRW has a 13,000 GVWR and the rear axle rating is 9650.

In later year models, the GVWR is 14K and the RAWR is 9750 for the chassis cab configuration (essentially no pickup bed from the factory, but there are other changes as well).

At any rate, having a 14K GVWR and a RAWR above 9500 pounds is not "very high" but rather it's the norm for modern DRW pickup trucks.

In 14 years of RV traveling, I owned two diesels powered 3500 RAM dallies. Both had LT235/80R17 LRE tires. I always ran them at the vehicle manufacturers recommendations. In all that time I only used 4 sets of tires. If I was going to lose tires, it was not going to be from under inflation.

Some manufacturers are now providing supplemental inflation pressure decals mounted next to the tire load and PSI placard.

[Tireman9]

Originally Posted by CWtheMan

The correct inflation pressures for original equipment tires fitted to vehicles built under the guidance of FMVSS standards are found on the vehicle certification label, the tire load and inflation placard and in the vehicle owner's manual. Sometimes, not very often, vehicles may have a supplemental placard affixed next to the load & inflation placard. Usually, it's there on half ton pick-up trucks that have OE Passenger tires.

The FMCSA standards are written for the trucking industry and are not interchangeable with FMVSS standards.

Background: Tire manufacturers design and build tires to serve the needs of the industries where they are used. Vehicles built under the guidance of FMVSS have OE tires fitted to them by the vehicle manufacturer. The vehicle manufacturer has the sole responsibility for OE tire selections and fitments.

Original Equipment Tires fitted to RV trailers and all other FMVSS built vehicles are considered by NHTSA to be a minimum standard. Therefore, the tire industries standard for replacement tires is: NEVER use tires smaller than the OE tires. The replacement tires MUST provide a load capacity equal to or greater than the OE tires provided.

Load index numbers on ST & LT tires are there for the sole purpose of identification of a speed letter, such 94S. The official load capacity for ST & LT tires is the load range lettering system.

President Trump threatened offshore ST tire manufacturers with increased tariffs if they did not start identifying tire speed ratings. He gave them two options, comply with NHTSA lettering standards or mold the tire speed rating on the tire sidewall.

Attachment 43098 Attachment 43099

Interesting. I thought the Federal Trade Commission responded to complaints on low cost Passenger car tires being "Dumped" into the US market in years prior to 2016 and the FTC response was to apply import duty on tires that did not have a speed rating. As a tire design engineer, I do not recall having to check mold stamping information against FMVSS but only confirm that any tires that we imported were speed rated.


Load Range is a replacement for the old outdated "Ply Rating" and has no functional relationship with the Speed Symbol that is based on a passenger car test designed by SAE to test tires up to a certain speed for 10 minutes at 88% of the tire max load.


Maybe I missed the regulation in FMVSS or TRA Yearbooks that ties Load Index number with the speed Symbol. I am willing to be educated on that topic if you would be so kind as to direct me to the appropriate regulation reference.

[gearhead]

So If my Ram dually has a payload of 5400 # and the yellow tag says inflate to 65 rear and 80 front, I should air the rears to 80??

[Tireman9]

.not enough information to give an informed answer.

[CWtheMan]

Originally Posted by gearhead

So If my Ram dually has a payload of 5400 # and the yellow tag says inflate to 65 rear and 80 front, I should air the rears to 80??

Yes! Unless your RAM has a supplemental tag for "normal loads.

Post # 48.

[CWtheMan]

Originally Posted by Tireman9

Interesting. I thought the Federal Trade Commission responded to complaints on low cost Passenger car tires being "Dumped" into the US market in years prior to 2016 and the FTC response was to apply import duty on tires that did not have a speed rating. As a tire design engineer, I do not recall having to check mold stamping information against FMVSS but only confirm that any tires that we imported were speed rated.

It was stipulated in the president's message.


Load Range is a replacement for the old outdated "Ply Rating" and has no functional relationship with the Speed Symbol that is based on a passenger car test designed by SAE to test tires up to a certain speed for 10 minutes at 88% of the tire max load.

The primary rule for displaying a speed letter on any tire is within the tire's service condition.


Maybe I missed the regulation in FMVSS or TRA Yearbooks that ties Load Index number with the speed Symbol. I am willing to be educated on that topic if you would be so kind as to direct me to the appropriate regulation reference.

We have discussed these points in other forums, and I provided references. FastEagle has been around a long time.

[jasin1]

Originally Posted by gearhead

So If my Ram dually has a payload of 5400 # and the yellow tag says inflate to 65 rear and 80 front, I should air the rears to 80??

I realize you don’t agree with this,i’m just answering this post because i tried to multiquote CW and tiremans post

I would always inflate to the sticker on the door whether it’s a single yellow sticker or one with light and heavy loads
i think a lot of these arguments are based on srw vehicles where the tires are expected to carry the load of the vehicle with no room for error…in a dual wheel configuration the four tires are way over the actual necessary capacity to support the load. The manufacturer chooses the tires for a number of reasons ..aesthetic’s,performance and capability and also the entire tire system is part of the overall engineered suspension system for ride quality and handling.
If you inflate your tires as tight as snare drums on a dually and have to lock up brakes on a bumpy old road you can easily get out of control and as long as you stay with oem tire sizes then your right to inflate to the placard.

Here is from Bridgestone tires website regarding max inflation vs door sticker
and Goodyear also

And unless we are talking about tires floating in midair with nothing attached or single wheel wheel barrows you should always go by the door sticker as it’s part of the millions of dollars of engineering that goes into a car or trucks handling and performance
If you go with aftermarket wheels and tire sizes you have pierced that engineering bubble and need to consult the tire manufacturer

I sometimes feel that people focus too much on a individual piece of the overall design….if you take a 2x4 board and look at its weight carrying characteristics you will see it’s pretty low…but if you look at roof trusses or floor trusses built with 2x4s you will see they are engineered as an overall system to carry much more weight.

[jasin1]

Originally Posted by CWtheMan

Yes! Unless your RAM has a supplemental tag for "normal loads.

Post # 48.

see post #54 ..i have great respect for your knowledge on the subject but here is my take.

[rhagfo]

Originally Posted by gearhead

So If my Ram dually has a payload of 5400 # and the yellow tag says inflate to 65 rear and 80 front, I should air the rears to 80??

Originally Posted by CWtheMan

Yes! Unless your RAM has a supplemental tag for "normal loads.

Post # 48.

I say wrong!
The Payload sticker on that 2018 Ram 3500 DRW will state for that 5,400# payload you inflate the tires to 65 psi!

[CWtheMan]

Originally Posted by rhagfo

I say wrong!
The Payload sticker on that 2018 Ram 3500 DRW will state for that 5,400# payload you inflate the tires to 65 psi!

Are those values from a supplemental decal?

Are you using a load inflation chart to come-up with 65 PSI?

[gearhead]

Originally Posted by CWtheMan

Are those values from a supplemental decal?

Are you using a load inflation chart to come-up with 65 PSI?

That's from the yellow sticker on the post, the silver sticker on the door says the same thing.
I don't have a clue if there is a supplemental sticker, never noticed one.
I have never aired the rears up to 80, and won't.
I have seen a load inflation chart but used it as casual reading.
The 65 came from the yellow sticker.
I dreamed up my own low load value. I'm running 40-42 on the rears right now.

[CWtheMan]

One can write and write and write about tires and never change the mind-set of the reader.

There are different regulations for different vehicle types. This is about tires fitted to vehicles that are manufactured under the guidance of the Federal Motor Vehicle Safety Standards (FMVSS) which also includes RV trailers.

Very seldom can information from those standards be addressed and correctly applied when used out of context. That context https://www.ecfr.gov/current/title-4...-V/part-571may include information from different areas of the 49 CFR part 571 (eCFR :: 49 CFR Part 571 -- Federal Motor Vehicle Safety Standards).

By nature, FMVSS standards ensure vehicles conform to all Minimal standards applicable to the topic. Here, tires are the topic. When put into context with all pertinent FMVSS standards you will find that the vehicle manufacturer has the sole responsibility for Original Equipment (OE) tire fitments. That includes setting recommended cold tire inflation pressures for that fitment. No matter what designated size tire is used for replacement purposes, the OE recommended cold inflation pressures will always be the guide for determining the load capacity of the replacement tires.

Because the FMVSS is guiding minimal requirements, the OE tire designated size and it’s recommended cold inflation pressure is the MINIMUM requirement.

OE tires fitted to a RV trailers are not required to provide (by regulation) any load capacity reserves. Most new RV trailer consumers are not familiar with load capacity reserves. Automotive tires are fitted with a percentage of load capacity reserves as directed in FMVSS. So, your cars, SUVs, and pick-up truck tires have load capacity reserves added to the fitment by the vehicle manufacturer.

Standard NHTSA tire safety PDFs will have a statement about correct OE tire inflations. It will tell you that the vehicle manufacturer’s recommendations found on the federal certification label, on the vehicle load and inflation placard and in the vehicle owner’s manual are the correct minimum requirements for that vehicle.

Tire load inflation charts are provided by tire manufacturers and are standardized by the Tire & Rim Association (TRA). Their primary purpose is to act as a quick reference for the installers of OE tires to use when determining and setting cold recommended inflation pressures for your vehicles. They are also necessary for installers fitting plus sized tires to your vehicles. I’m not going to get into that procedure because trailer manufacturers seldom recommend replacement tires other than the OE tire designated sizes. In the trucking industry they are used to ensure a loaded truck has enough inflation pressure across the axles for the load they are carrying. Tire design is a factor for that industry.

The values provided within a load inflation document are not recommendations. Vehicle builders and tire installers for the industry set recommended cold inflation pressures from the factual information the load inflation charts provide.

I know I lose reader interests after about 50-75 words. Good Luck.

[travelin texans]

Originally Posted by gearhead

That's from the yellow sticker on the post, the silver sticker on the door says the same thing.
I don't have a clue if there is a supplemental sticker, never noticed one.
I have never aired the rears up to 80, and won't.
I have seen a load inflation chart but used it as casual reading.
The 65 came from the yellow sticker.
I dreamed up my own low load value. I'm running 40-42 on the rears right now.

If I recall my GMC stated 75 front/70 rear which is where I inflated them towing or empty, too lazy to constantly readjust pressures.
I don't know what tires you have but if 65 psi is recommended & you're running 40-42 in my opinion they are considerably under inflated.
But this subject goes on forever & nothing ever is agreed upon other than everyone has different options or preferences as to what works for them & none of them are as per the official regulations.