Tire pressure tt vs tire max psi

[60sumtin]

Originally Posted by Tireman9

Very few RV tires wear out before they age out and center wear you are talking about was more of a problem on Bias tires.

For this situation ogreplacing C rated tires he has a couple of choices.
1. Get D rated and inflate to at least 50
2 inflate to 65 for tire life on multi axle trailer

Thank you.

[FastEagle]

The simple truths about RV trailer tire inflation pressures.

How are they determined? Tires are manufactured with a collaboration between tire manufacturers and vehicle manufacturers. Each size designation has standardized specifications including tire inflation charts divided in increments. Vehicle manufacturers use the tire inflation charts when setting recommended tire inflation pressures for original equipment fitments. Vehicle manufacturer’s are solely responsible for setting recommended tire inflation pressures for all vehicles they build. Building instructions are written to insure minimal acceptable standards are met. The inflation standard tells the vehicle manufacturer to set a recommended cold inflation pressure that is appropriate for the vehicle fitment. Therefore, that recommendation becomes the minimum standard for the Original Equipment tires and all subsequent replacements.

Under inflation is something less than what is recommended on the vehicle’s placard. Over inflation is something more than what is needed to achieve maximum load capacity from the tire, which is molded onto each tire.

Anyone can recommend anything in-between minimum and maximum inflation pressures.

When using replacement tires that do not conform to the vehicle tire placard it is often necessary to set a new recommended cold inflation pressure for the replacements. Tire industry standards have procedures to follow for that event. Of primary importance is meeting the very basic needs of the vehicle. That is done by never using replacement tires that do not have a load capacity ability to meet the standards of the OE tires.

For plus sized replacements, auxiliary tire placards are allowed. A savvy tire installer will make notations in the vehicle owner’s manual and place an auxiliary tire placard adjacent to the original, displaying the new tire size and it’s recommended cold inflation pressure.

You’ll have to do a lot of searching before you find that savvy installer.

IMO, a trailer tire is any tire the vehicle manufacturer deemed appropriate for fitment to the trailer and certified it on the vehicle certification label.

[Rednax]

Originally Posted by Old-Biscuit

Then take some sidewalk chalk and rub a thick chalk line across width of tire thread

Drive forward 25' then back up 25' and check chalk line on tires.

Worn off in center area..TOO much pressure for actual weight on tires (over-inflated)
Small contact patch, lousy braking effect, center of thread wears out

Worn off at edges of tires...too little pressure (under inflated)
Excessive heat build up/fast wearing

Worn off equally across the thread....Just right
Weight/psi match..best for braking, thread wear, tire loading

Not in trailer service.

Roger Marbles in his career as a tire engineer went thru more than 10,000 carcasses to deliver opinions.

Matching tires to TT starts with individual wheel loads. TT loaded up, and WD applied. Not one position will be the same as the others in a scale reading.

The heaviest position determines all else in tire spec.

It’s my opinion that ST aren’t worth the money. An LT is a better choice than the Johnny Come lately “spec” that keeps old tire machinery at work. But is illegal to use on a passenger vehicle. QC is sloppy.

Brand name and country of origin don’t matter. It’s the rating.

[60sumtin]

Originally Posted by Rednax

Not in trailer service.

Roger Marbles in his career as a tire engineer went thru more than 10,000 carcasses to deliver opinions.

I would say Roger has seen enough evidence through the course of his career that his comments on these boards and his blog posts are more than just his opinion.

[Cowpie1]

I like following load pressure charts from the tire maker on the particular tire I am using. They put in all the R&D and probably have it figured out what is the best pressure to run their tire based on the load put on it. That is usually what the trailer maker uses on the placard for the tire they put on at the factory. Going to different style, brand, type of tire would negate that.

[60sumtin]

Originally Posted by Cowpie1

I like following load pressure charts from the tire maker on the particular tire I am using. They put in all the R&D and probably have it figured out what is the best pressure to run their tire based on the load put on it. That is usually what the trailer maker uses on the placard for the tire they put on at the factory. Going to different style, brand, type of tire would negate that.

Seems logical though to have the tire pressure set to the load rather than the sidewall's maximum pressure. Doing so should result in a larger contact patch to the road.

I've weighed what typically goes into our trailer so I know I'm about 900 pounds less than the GVWR. I just don't know what the actual trailer weighs empty, only what it says on the info sheet inside the trailer. How the two compare I don't know but I suspect not too much different. The nearest CAT scale is 150 miles away so its not exactly convenient to find out.

I need to buy new tires this spring, I just haven't decided what to buy yet but I will consider the Goodyear Endurance even though Goodyear has made their own home grown "bombs".

After reading Roger's latest blog post I got wondering what my maximum wheel pressure was so I pulled off the spare. The maximum air pressure wasn't marked, only the weight limit which is the same 1820 pounds as the OEM Marathons that came with the trailer. If I go with the Endurance (they don't come in LR-C) I'll heed his advice and keep the maximum inflation to 50 PSI even though a LR-D tire may be 65 PSI. Glad I read his article as I might have over inflated the wheel. Me thinks its best to err on the side of caution.

[Cumminsfan]

Originally Posted by 60sumtin

Seems logical though to have the tire pressure set to the load rather than the sidewall's maximum pressure. Doing so should result in a larger contact patch to the road.

I've weighed what typically goes into our trailer so I know I'm about 900 pounds less than the GVWR. I just don't know what the actual trailer weighs empty, only what it says on the info sheet inside the trailer. How the two compare I don't know but I suspect not too much different. The nearest CAT scale is 150 miles away so its not exactly convenient to find out.

I need to buy new tires this spring, I just haven't decided what to buy yet but I will consider the Goodyear Endurance even though Goodyear has made their own home grown "bombs".

After reading Roger's latest blog post I got wondering what my maximum wheel pressure was so I pulled off the spare. The maximum air pressure wasn't marked, only the weight limit which is the same 1820 pounds as the OEM Marathons that came with the trailer. If I go with the Endurance (they don't come in LR-C) I'll heed his advice and keep the maximum inflation to 50 PSI even though a LR-D tire may be 65 PSI. Glad I read his article as I might have over inflated the wheel. Me thinks its best to err on the side of caution.

[cherv]

We have steel 14" rims and oem tires max inflate to 50 psi. New tires max inflation 65 psi.. No problem with rims at that psi.. Aluminum rims a different story

[rarebear.nm]

Everyone can inflate their RV tires however they wish- I guess. On multiaxle trailers there are shear forces that are unique to these axle configurations. My strong advice is to inflate tires on multiaxles trailers only, to the Max Pressure molded into the side wall. Do not go by inflation charts or RV vendor data. If in doubt see post 28 above. This is very good advice and you are still not sure then do some web research on tire interplay shear. On multiaxle trailers the issues are in part what's happening to the structure of the tire's sidewall in turns, much more so in tight radius turns. You need the pressure to reduce damage to the tires.

I know some folks have towed for the last 100 years by inflating to .... and have had no problems. That's great for them, but the best general advice is to follow the above guidelines.

Another good information link for tires questions is:

Roger Marble Archives - RV Travel

[Tireman9]

I do wish FASTEAGLE'sa post about trailer companies and tire companies working together were true.
While Car and truck mmfgdo consult and work with the tire companies and the tires supplied for OE application on regular vehicles are fine tuned with the chassis of the car.
Trailers are a different story. RV companies do not have staff tire engineers as do GM, Ford, Chrysler, Honda, Toyota, Subaru, Mazda, Lexus, Fiat, BMW etc. I know as I have worked with each of the above but I have never worked with an RV company and I have never heard of any tire company developing a tire for a specific trailer application. That costs money and the trailer companies are all about the bottom line.
Interply Shear is unique to radial tires. That is the force that tears the belts apart. Maybe if you read THIS post on why tires fail or the posts on the Internet about Interply Shear, or THIS post on why some trailers should inflate based on load but others would be better off running higher inflation, you would realize that you need to pay attention to the details if you want longer tire life.

Multi-axle trailers are NOT the same as single axlew trailers or as regular motorized vehicles. If or when you suffer a belt separation "Blowout" please do not post a complaint here and expect simpathy from me. I feel like a broken record.

[60sumtin]

Originally Posted by Tireman9

Interply Shear is unique to radial tires. That is the force that tears the belts apart. Maybe if you read THIS post on why tires fail or the posts on the Internet about Interply Shear, or THIS post on why some trailers should inflate based on load but others would be better off running higher inflation, you would realize that you need to pay attention to the details if you want longer tire life.

Multi-axle trailers are NOT the same as single axlew trailers or as regular motorized vehicles. If or when you suffer a belt separation "Blowout" please do not post a complaint here and expect simpathy from me. I feel like a broken record.

Roger, so what you're saying is the Goodyear Endurance Load and Inflation chart you provided here should NOT be used with multi-axle trailers? If so that chart is missing some crucial information as I suspect the vast majority of those tires built are being installed on multi-axle trailers. If because of interply shear the Load and Inflation chart is only safely applicable to single axles trailers it should be noted as such.

Or maybe my limited layman's knowledge is not grasping what's being said.

[cruzbill]

I run the max sidewall pressures on my 21' TT, on our MH, I got 4 corner weights and run per the tire mfg weight table, plus 5psi.

[Tireman9]

Originally Posted by 60sumtin

Roger, so what you're saying is the Goodyear Endurance Load and Inflation chart you provided here should NOT be used with multi-axle trailers? If so that chart is missing some crucial information as I suspect the vast majority of those tires built are being installed on multi-axle trailers. If because of interply shear the Load and Inflation chart is only safely applicable to single axles trailers it should be noted as such.

Or maybe my limited layman's knowledge is not grasping what's being said.

Not quite. The Load/Inflation chart is valid. The problem is that I have yet to see or hear of an RV assembler use Finite Element analysis to learn what is happening to the tires on their multi-axle trailers.
Up untill this year most RV assemblers just selected tires that had zero to only a small measure of margin of tire load capacity over the GAWR. I even ran into one application where the tire stated load capacity was slightly under the DOT regulations but the Rv company avoided a recall by getting the tire importer to issue a letter to DOT claiming the tire was capable of a few more pounde load than the number on the tire sidewall. Of course this would mean the owner would be required to replace the tires and only use the identical tires assuming they could even find them.
Now due to RVIA new policies they are suppose to ensure the tire rating is 110% of the GAWR. This increased margin doesn't necessarily mean you are getting larger capacity tires as this margin can easily be met by simply derating the axle GAWR by a few hundred pounds. I bet there isn't a trailer owner out there that compared the capacities of a 2016 vs a 2018 model of the same trailer to see where the extra 10% came from.

The Load inflation tables for ST tires hasn't changed since the 60's as far as I can tell. The numbers are still valid BUT if you want more than 2 or 3 years life on your tires, you need to do something to allow the radial tires to tolerate this extra belt loading.
I believe that GY incorporated Nylon belt caps, strips or layers to help the belts absorbe this extra shear without failing. But there is still a limit of what the rubber can tolerate even with the Nylon reinforcement. Maybe the Nylon adds a year to the tire life. I haven't seen any direct comparison test data.

One approach to lower the Shear forces is to lower the load significantly (maybe a 20% load margin would be enough to get 5 years out of a tire with Nylon cap on multi-axle trailer. Maybe you would need 25% or more margin) There is technology available to the industry now and with their "super-Computers it might be able to predice what is needed to deliver longer tire life. From the calculations I ran before I retired I do know that increasing inflation will lower (but not eliminate) the extra shear forces.

IMO as long as no one is willing to offer a 3 - 5 year warranty on belt durability on ST tires there are no strong incentives to change the construction or load margin requiremnets for multi-axle trailer application.

Hope this helps your understanding of the situation.

[Tireman9]

Originally Posted by roady

Read this article for some information
https://www.linkedin.com/pulse/tire-...t-andy-newton/

Most of the info is correct but when he says "When it comes to tire air pressure, it is my understanding that every brand, model, and size of tire has its own pressure requirement based on load and use." He missed the boat. When you look at the tables you will find that identical size & Load range tires all support the same load when inflated to the same lever with very few exceptions. Most of which are from Michelin and theyonly vary by maybe +/- 5 psi. or a couple hundred pounds capacity for larger tires.
If you need to review the tables for your tires you should be able to find the info you need HERE.