tire pressure

CALandLIN wrote:
Tire inflation pressures are not supposed to be as complicated as they are often presented in this form of discussion. …..

This ^^^^^

Unfortunately, trailer manufacturers haven't done a good job in the past with sizing the tires specified for their vehicles. The car manufacturers got it done by the 1990's all on their own. Pickup trucks, vans, and SUV's were done by 2008 as a result of the Ford/Firestone thing.

So we spend a lot of verbiage on trailers tires - and complicating the issue is that trailers are unique in that they are close to fully loaded pretty much all the time.

I think we are seeing the light at the end of the tunnel. The trailer tire manufacturers are changing their tires to bring them up to snuff, and trailer manufacturers are doing a better job of sizing. Hopefully in 10 years time, the discussion about tires on trailers will be closer to what we see when talking about passenger cars.

Tire inflation pressures are not supposed to be as complicated as they are often presented in this form of discussion.

Most of the misunderstandings comes from complicating the subject with unneeded information.

For more than 99% of the vehicles in this thread, the governing body is the DOT via NHTSA and their FMVSS. The industry standards are from the automotive & tire industries.

Recommended, a key word in tire inflation pressures. It’s the best fit. You inflate your tires in the morning to a recommended cold inflation pressure you’ve been told to use. Then you get underway. After a mile or two the pressure has climbed to a higher value, as it’s supposed to do. You cannot correctly set it again until the tire cools.

So, where did the original recommendation originate? The governing body, with it’s wisdom, determined that the vehicle manufacturer is the most qualified for that task and has given them the sole responsibility for setting cold recommended tire inflation pressures for all Original Equipment (OE) tires. Once certified to a particular vehicle, the recommendation is passed on to all replacement tires and supported by an industry standard that simply says that replacement tires must provide an inflation pressure equal to, or greater than what the OE tires provided with the vehicle manufacturer recommended cold inflation pressure found on the vehicle certification label.

Now some problem areas. Special circumstances and options. Foreseen special circumstances are normally identified by the vehicle manufacturer and will be outlined in the vehicle owner manual. Optional conditions are often whims for load variations or even a more comfortable ride condition. Circumstantial & optional conditions have one thing in common, they should never be below the vehicle manufacturers certified recommendations or higher than the inflation pressure needed for maximum tire load capacity. Reference for that can be found in the USTMA publications or in just about any major tire manufacturer’s Standards of Operations Procedures (SOP) manuals and/or tire data books.

Another problem, commercial tires. They, when used on commercial vehicles are inflated differently. The commercial regulations (FMVSA) inflate to the load carried. They do not have a provision for a normal “recommended cold inflation pressure”. Many of those tires are used on large RV trailers and Motor Homes. When those vehicles are built and certified to FMVSS standards the commercial regulations are not applicable. In the case of RV trailer tire fitments, any design used becomes a trailer tire. The vehicle certification label displays the tire’s designated size. It is the standard for that trailer. The vehicle manufacturer can (maybe, or not often) recommend options.

Just about any mechanical thing we use has limits. In this context, those limits are normally well documented. Beyond those limits is the gray or unknown factors. When we enter into those areas, we can go too far, because we don‘t know how far to go, unsatisfactory things may - probably will - happen.

Bottom line; For RV trailer tires, always use the trailer manufacturer’s recommended cold inflation pressures. Make sure all replacement tires have a load capacity via inflation pressure that equals or exceeds the load capacity the OE tires provided at the vehicle manufacturers recommended cold inflation pressures. USE steel valve stems.

"but also our experience says that ALL tires shouldn't be loaded to more than 85% of their rated capacity."

I have NEVER had a tire problem running tires at MAX if needed or 5psi over what the load dictates. But my inflations are based on weight every time.

I did have a GY "H" loose some of it's center tread but that had ZERO to do with inflation. Yes they did replace the tire.

Some get freaked out that I run full RAWR of 9,750# on my DRW RAM, but that is what it's rated for. These "RATINGS" already have a safety margin built in!!!

Run quality tires and they will hold up to do the job, POS is POS.

CapriRacer wrote:

fj12ryder wrote:
Okay, let me get this straight: you, Tireman9, and CapriRacer say it's bad to run lower than max air pressure regardless of weight loadings.

Goodyear publishes tire pressure charts to use if you're not towing max weights. They have these charts for motorized vehicles and towed vehicles. But now you all say those charts and Goodyear are wrong, and not to be used, even though they specifically say they are for RV trailers.

Why does Goodyear list varying pressures for ST tires based are carried weight. Those ST tires go on "Trailers". Why should we obey you three and not listen to Goodyear who actually makes tires?

Goodyear specifically says "The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs." It specifically says "trailer", not "truck/MH/class A/class C/Van/etc with tires at the corners" but trailers "with close spaced axles".

Why doesn't this conflict with your opinions that trailers should always run max sidewall pressure regardless of weight. No offense, but you guys are voicing your opinions, as opposed to what Goodyear says should be done. Excuse me if I give more weight to a real tire builder over some RV forum posters. If I see that Goodyear has changed their stance on varying pressures for varying weights, then I will give your opinions more credence.

Til then we'll just have to agree to disagree.

First, those charts are MINIMUMS, not recommendations. So from that perspective, there isn't a conflict.

Second - and I am pretty sure Roger and I are on the same page - our recommendation to use the max sidewall pressure for ST tires (and LT tires used on trailers) comes with some caveats.

The idea is to reduce the interply shear forces. Also included is the experience that not only have trailers been specified with tires that don't have enough load carrying capacity, but also our experience says that ALL tires shouldn't be loaded to more than 85% of their rated capacity.

Further, there are situations where using the max sidewall pressure would not be our recommendation, but it's difficult to describe when that situation exists - hence the appearance of a monolithic statement.

So, overall, there isn't any conflict between what Roger and I are saying, and what Goodyear is publishing.

An excellent explanation and far from what has been posted before by a different person. You've explained that your views are not carved in stone and can be amended for certain situations. That certainly sounds very reasonable and not a "my way or the highway" type of outlook.

Thank you for a rational explanation.

Okay, let me get this straight: you, Tireman9, and CapriRacer say it's bad to run lower than max air pressure regardless of weight loadings.

Wrong again.
Read what I have posted twice now what rvsafety and Goodyear says about towable rvs tire pressures.

Also read Tireman9 and CapriRacers blogs on tire safety for their input.

Now if the trailer owner has followed recommended practice of using tires with 10-20 percent capacity above axle ratings then yes max pressures work better over derating to a minimum pressure chart number.

fj12ryder wrote:
Okay, let me get this straight: you, Tireman9, and CapriRacer say it's bad to run lower than max air pressure regardless of weight loadings.

Goodyear publishes tire pressure charts to use if you're not towing max weights. They have these charts for motorized vehicles and towed vehicles. But now you all say those charts and Goodyear are wrong, and not to be used, even though they specifically say they are for RV trailers.

Why does Goodyear list varying pressures for ST tires based are carried weight. Those ST tires go on "Trailers". Why should we obey you three and not listen to Goodyear who actually makes tires?

Goodyear specifically says "The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs." It specifically says "trailer", not "truck/MH/class A/class C/Van/etc with tires at the corners" but trailers "with close spaced axles".

Why doesn't this conflict with your opinions that trailers should always run max sidewall pressure regardless of weight. No offense, but you guys are voicing your opinions, as opposed to what Goodyear says should be done. Excuse me if I give more weight to a real tire builder over some RV forum posters. If I see that Goodyear has changed their stance on varying pressures for varying weights, then I will give your opinions more credence.

Til then we'll just have to agree to disagree.

First, those charts are MINIMUMS, not recommendations. So from that perspective, there isn't a conflict.

Second - and I am pretty sure Roger and I are on the same page - our recommendation to use the max sidewall pressure for ST tires (and LT tires used on trailers) comes with some caveats.

The idea is to reduce the interply shear forces. Also included is the experience that not only have trailers been specified with tires that don't have enough load carrying capacity, but also our experience says that ALL tires shouldn't be loaded to more than 85% of their rated capacity.

Further, there are situations where using the max sidewall pressure would not be our recommendation, but it's difficult to describe when that situation exists - hence the appearance of a monolithic statement.

So, overall, there isn't any conflict between what Roger and I are saying, and what Goodyear is publishing.

Since we are letting our opinions be known, you will never see a Goodyear tire on anything I own. Trailer or automobile tire. I had one blow out that was still bolted to the spare tire carrier on my trailer. It blew itself to shreds along with the cover. I had a Goodyear car tire on my wifes T-Bird throw a 4 inch wide strip of rubber out of the center. Maybe they do make tires better now. The st (sucker tire) marathons they produced for trailers should have been outlawed as well as some of their automobile tires. Just my opinion mind you.:)

Okay, let me get this straight: you, Tireman9, and CapriRacer say it's bad to run lower than max air pressure regardless of weight loadings.

Goodyear publishes tire pressure charts to use if you're not towing max weights. They have these charts for motorized vehicles and towed vehicles. But now you all say those charts and Goodyear are wrong, and not to be used, even though they specifically say they are for RV trailers.

Why does Goodyear list varying pressures for ST tires based are carried weight. Those ST tires go on "Trailers". Why should we obey you three and not listen to Goodyear who actually makes tires?

Goodyear specifically says "The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs." It specifically says "trailer", not "truck/MH/class A/class C/Van/etc with tires at the corners" but trailers "with close spaced axles".

Why doesn't this conflict with your opinions that trailers should always run max sidewall pressure regardless of weight. No offense, but you guys are voicing your opinions, as opposed to what Goodyear says should be done. Excuse me if I give more weight to a real tire builder over some RV forum posters. If I see that Goodyear has changed their stance on varying pressures for varying weights, then I will give your opinions more credence.

Til then we'll just have to agree to disagree.

It does make you wonder why they choose to post conflicting information. Since right here is the conflicting part: RV Tire and Care Guide

And, if lessening the air pressure is bad for the tires, why would any tire company give you the chart to set your pressure to the weight being carried by the tire? Or do you know some secret the tire people don't know? Do you suppose they purposely are tying to ruin your tires by giving false data?

No conflict when you read it all and also understand a rv can be a trailer with close spaced axles vs a truck/MH/class A/class C/Van/etc with tires at the corners. Both require a different approach to tire pressure needs for different rv types.

Tireman9 and CapriRacer both have explained all this before on their tire blogs and on our website forums. Tireman9 rvtiresafety blog has pages of reading on reasons our trailers have different pressure needs vs non trailer types or our trucks.
I still like the advice posted above from rvsafety.com.
Use max sidewall unless this causes a severe over inflation issues. If this is your situation allow a 10 – 15psi safety margin above the minimum required inflation pressure (minimum load pressure chart).
Pretty much what Goodyear also says about towable rvs.

Do what you want. Inflation tables are there for a reason.

Know each tires weight.