Yet another tire pressure question

[Tireman9]

Originally Posted by old40ford

I thank you for your information and all the help you have given me. I purchased the 600 series for my car hauler and I guess that is all that I can do as it has aluminum wheels and not enough room for metal stems as far as I can tell.
thanks again, I appreciate your help.
John

Quick Google search or on eBay


"metal bolt in valve stems"


There are some short stems that are probably shorter than the 600 series.




https://shop.advanceautoparts.com/p/...B&gclsrc=aw.ds

[17 Oaks]

Originally Posted by dlwilliams48

My "old" tires were china bombs with a max inflation of 50 psi, which is what I put in them. The new Carlisle LR D tires say max psi 65#. My trailer is not a heavy trailer, maybe 7000 lbs loaded. I'm thinking of maybe 55 psi to start. Any idea where I could check to see if this is reasonable or if I should go to maybe 60 psi?

The max AP is the AP at which that tire will carry its max rated load and provide the proper contact patch.

Its all about the contact patch.

On my off road Jeep with its 37x12.50x17 BFG KM2's the Max weight load was about 3100 lbs IIRC, forgot the AP, but very high, around 65 lbs or so.

BUT in order for my Jeep which weighed about 4800 lbs, so 2 tires would support the entire weight of the Jeep. But this would have put me riding on the very center of the tire, not good for traction or handling, rain or anything else.

It took only 16 lbs of AP to give me a FULL contact patch and that is what I ran on my drives to my off road adventures and I put almost 100,000k miles on that Jeep from Dallas Tx across the SW. Off road I ran 5 lbs which increased my contact patch by about 25% and allowed the tire to 'wrap' around obstacles better.

Take away: Put 65 lbs of AP in those new tires then look at your contact patch, form there you can decrease the AP to achieve a full contact patch and ride with safety within the parameters of your tires safety envelope.

How to determine the contact patch: Drive your vehicle with dry tires thru a parking lot water puddle or drive thru some dust and look at the wet/dusty patch on your tires it should edge to edge evenly. If just a center line let air out , try 5 lbs on the first go. If the contact patch is wet/dusty on the outer tread and less in the middle you will need to add, but if you start with the max then you should have no issue.

Let us know how it works out for ya!

[irishtom29]

Originally Posted by Airdale

That's not even close to the established tire fitment procedures for RV trailer tires.

Misuse of the word fitment is a pet peeve of mine.

[Airdale]

Originally Posted by irishtom29

Misuse of the word fitment is a pet peeve of mine.

The word "fitment" is widely used throughout the tire industry. You will find its usage in any of the numerous tire manufacturer's tire data books.

[Tireman9]

General comments.
All discussion on inflation pressure or "maximum air Pressure" is refering to the "cold" inflation pressure and NEVER the Hot or even warm pressure.
Tire out of the sun and not driven on for AT LEAST two hours.
I would consider anything shorter than TWO HOURS to not be 'COLD".




Chalk across tread is ok for a quick alignment check but is not accurate enough to set pressure by. There are some tires with a concave tread even with the pressure number on the sidewall used as the inflation pressure.


Over half the the RVs that have actually been on individual tire scales have been fount to have a tire in overload and/or an axle in overload and/or the RV in overload.


I have been reading a variety of owner's manuals. Especially the section on "Tire Safety". Bet fewer than a couple percent of owners could quote any of the inflation, load or tire life info in their owner's manual.


RE GYE ya they are probably better than GYM BUT how many folks have run them for 3 years or 20,000 miles? You can't compare the durability of a 1 year old tire with thousands that have been run for 4 - 6 years with a good % of the time in overload or underinflated.
IMO only after we get a few hundred GYE in use for 3 to 4 years with 15,000+ miles will we START to get meaningful comments on their durability.

[Airdale]

Originally Posted by 17 Oaks

The max AP is the AP at which that tire will carry its max rated load and provide the proper contact patch.

Its all about the contact patch.

On my off road Jeep with its 37x12.50x17 BFG KM2's the Max weight load was about 3100 lbs IIRC, forgot the AP, but very high, around 65 lbs or so.

BUT in order for my Jeep which weighed about 4800 lbs, so 2 tires would support the entire weight of the Jeep. But this would have put me riding on the very center of the tire, not good for traction or handling, rain or anything else.

It took only 16 lbs of AP to give me a FULL contact patch and that is what I ran on my drives to my off road adventures and I put almost 100,000k miles on that Jeep from Dallas Tx across the SW. Off road I ran 5 lbs which increased my contact patch by about 25% and allowed the tire to 'wrap' around obstacles better.

Take away: Put 65 lbs of AP in those new tires then look at your contact patch, form there you can decrease the AP to achieve a full contact patch and ride with safety within the parameters of your tires safety envelope.

How to determine the contact patch: Drive your vehicle with dry tires thru a parking lot water puddle or drive thru some dust and look at the wet/dusty patch on your tires it should edge to edge evenly. If just a center line let air out , try 5 lbs on the first go. If the contact patch is wet/dusty on the outer tread and less in the middle you will need to add, but if you start with the max then you should have no issue.

Let us know how it works out for ya!

Your post would be more acceptable if you used it within the parameters of acceptable inflation pressures. They are anything between what has been recommended for Original Equipment tires in the vehicle owner's manual and what is needed to gain the maximum load capacity from the tires (That's on the sidewall).

The acceptable industry wide definition for underinflation is a cold pressure reading below tire placard pressures. When that low inflation pressure gets to 20% below the placard pressure the tire is considered to be in "run flat" condition.

However, there is a double standard when applying FMVSS standards. When the vehicle manufacturer fits wheel/tire assemblies to automotive vehicles (self propelled) the standards requires them to have a percentage of load capacity reserves. When the RV trailer manufacturer - also abiding to FMVSS standards - fits wheel/tire assemblies to RV trailer axles the minimum value to fit to is the trailer's GAWR maximum limit. The standard actually says the fitment must be "appropriate" and set with recommended cold inflation pressures.

The tire industry provides charts so that vehicle manufacturer's can meet the requirements set forth in the standards. When used by individual owners, the charts are for the same purpose, to meet the minimum standards set in motion by the vehicle manufacturer.

[Tireman9]

RVIA ( shiney sticker next to your side door) in the past only required the tires be capable of meeting the GAWR. i.e. ZERO margin


In 2017 or late 2016 RVIA got better and required at least a 10% load margin of the tires greater than GAWR.


As a tire engineer I suggest 15% margin asa a minimum. Personally I am running 20 to 25% margin on my MH which doesn't have the same Interply Shear problem all multi-axle trailers do.

[Slow Moon]

My 2 cents to everyone here:

IF YOU WANT TO KNOW ABOUT RV TIRES AND HOW TO CARE FOR THEM, READ EVERYTHING TIREMAN9 SAYS & GO TO HIS CITED BLOG WHEN YOU HAVE QUESTIONS.

5th Wheel Tire Failures caused me to spend hundreds of hours on RV tire research. I have not found a better authority for us.

If we would all read and understand what Tireman9 writes here and on the cited blog, there would be a lot less uninformed, counterproductive, baseless garbage comments arising from anecdotes, bias and ignorance. Tire threads would be a lot shorter and way more useful.

[Iwannacamp]

Originally Posted by Tireman9

General comments.
All discussion on inflation pressure or "maximum air Pressure" is refering to the "cold" inflation pressure and NEVER the Hot or even warm pressure.
Tire out of the sun and not driven on for AT LEAST two hours.
I would consider anything shorter than TWO HOURS to not be 'COLD".




Chalk across tread is ok for a quick alignment check but is not accurate enough to set pressure by. There are some tires with a concave tread even with the pressure number on the sidewall used as the inflation pressure.


Over half the the RVs that have actually been on individual tire scales have been fount to have a tire in overload and/or an axle in overload and/or the RV in overload.


I have been reading a variety of owner's manuals. Especially the section on "Tire Safety". Bet fewer than a couple percent of owners could quote any of the inflation, load or tire life info in their owner's manual.


RE GYE ya they are probably better than GYM BUT how many folks have run them for 3 years or 20,000 miles? You can't compare the durability of a 1 year old tire with thousands that have been run for 4 - 6 years with a good % of the time in overload or underinflated.
IMO only after we get a few hundred GYE in use for 3 to 4 years with 15,000+ miles will we START to get meaningful comments on their durability.

I agree and DO NOT have the knowledge to speak/argue against your statement, but I think if the quality was lacking...we would have already heard of failures. They are "under the microscope"..so to speak.

Thanks again Tireman for what you do.

[coldbrew]

I have had these same tires for about 4 years now and have always inflated them to 65 psi. Never had one problem out of them.

[rlh1957]

Originally Posted by Tireman9

RVIA ( shiney sticker next to your side door) in the past only required the tires be capable of meeting the GAWR. i.e. ZERO margin


In 2017 or late 2016 RVIA got better and required at least a 10% load margin of the tires greater than GAWR.


As a tire engineer I suggest 15% margin asa a minimum. Personally I am running 20 to 25% margin on my MH which doesn't have the same Interply Shear problem all multi-axle trailers do.

I agree with your assessment and I never have put any confidence, trust or belief in anything RVIA says. They are only a puppet for what the RV manf want.

[ben31]

Originally Posted by rjshiflet

What he said ^

Just do it! When in doubt...put what is listed on the side of the tire!

[irishtom29]

Originally Posted by Airdale

The word "fitment" is widely used throughout the tire industry. You will find its usage in any of the numerous tire manufacturer's tire data books.

Yes, the word is widely misused. I blame this ironic error on pretentious syllable multiplication. This is also to blame for the common misuse of the word usage.

[Maingler]

go to the tire manufacturers web site. it will give you PSI and weight ratings for each tire.

[Modersical]

Tire Pressures

Each vehicle has a safety placard around the driver's door post stating tire size and air pressure recommendations based on the assumed gross vehicle weight. This is a baseline, starting point, and using these guidelines is a one size fits all mentality.

The max tire pressures listed on your tires is what is needed to support the maximum weight load that is printed on your tires, so you need to do a little calculation as to how heavy your vehicle can be, before you are overloaded, and then you need to know your actual scale weight, to know how much air pressure is needed to support your actual load, keeping a full, flat, footprint of tread on the road.

There are charts to determine how much tire pressure for any given load you are actually hauling for each tire size. If you are not hauling the maximum load, you do not need maximum air pressure, or your tires will be over inflated, kinda pooched out in the center, and your tread will wear unduly in the center.

I personally feel it would be better to have maximum/over inflation, than under inflation, and too soft and cushy of a ride, which will cause your tread to wear more on the edges, but a bigger problem with under inflation is tire squirm which causes your tire to overheat, delaminate, and self-destruct, as well as risking loosing the bead seal, and rolling the tire bead loose in heavy cornering.

Each vehicle weighs differently in everyday use depending how you fill your water tank and how much gear you tote around in your RV. Most of the time, we settle on a set number of things that we haul around, and it behooves us all to put our rigs on a scale to determine what kind of load your tires need to consider hauling around, to best know the tire pressure for supporting that particular load.

Before going to the scale, and after loading your usual gear, I fill my freshwater tank and fuel tank, and empty my gray and black water tanks, and put myself and my wife in our two front seats. That is the weight we usually run at, starting out. The fuel load gets lighter, but water load stays about the same . . . just gets redistributed to other tanks. This is our max weight, and the weight you can find in charts for the nearest air pressures that are needed to support your load safely, and keep proper tread footprint on the pavement.

I really like the chalk test the fellow above mentioned. That tells you what you need to know in practical application! In other words, you should get the same safe air pressure to both safely haul your load, and get maximum tire life.

[17 Oaks]

Originally Posted by Airdale

Your post would be more acceptable if you used it within the parameters of acceptable inflation pressures. They are anything between what has been recommended for Original Equipment tires in the vehicle owner's manual and what is needed to gain the maximum load capacity from the tires (That's on the sidewall).

The acceptable industry wide definition for underinflation is a cold pressure reading below tire placard pressures. When that low inflation pressure gets to 20% below the placard pressure the tire is considered to be in "run flat" condition.

However, there is a double standard when applying FMVSS standards. When the vehicle manufacturer fits wheel/tire assemblies to automotive vehicles (self propelled) the standards requires them to have a percentage of load capacity reserves. When the RV trailer manufacturer - also abiding to FMVSS standards - fits wheel/tire assemblies to RV trailer axles the minimum value to fit to is the trailer's GAWR maximum limit. The standard actually says the fitment must be "appropriate" and set with recommended cold inflation pressures.

The tire industry provides charts so that vehicle manufacturer's can meet the requirements set forth in the standards. When used by individual owners, the charts are for the same purpose, to meet the minimum standards set in motion by the vehicle manufacturer.

Your mixing apples and oranges. There are no Jeep Wranglers that come from the factory with 37x12.50 load range D tires, so by putting them on my '03 Jeep wrangler I way outside any parameters that Jeep OEM has for tires.

That said how do I calculate air pressure? Here the answer is simple, identify the contact patch, if its overinflated it will show up in the center, under on the edges, good patch is easy to identify and I gave a couple of methods I have used.

The contact patch is the vehicles connection with the surface. For street and highway use the 16 lbs worked on all 4 corners of my Jeep, for off road use I ran 3-5 lbs max.

Identifying the contact patch thru a manual means such as stated is not something I read in Cars B Us monthly mag, last week. Been doing it all my life and learned it from my dad, who had done it all his driving life going back to his first car, a Model T.

Yes, go out to my shop and you can find a large air compressor and assorted air gauges from digital to analog and I like many have the ability to add as little as a .5 lb of air if need be. But this has not been the case for a good deal of my life and certainly in my dad's time not all all. You pumped up a tire using a hand pump and few had gauges of any kind and the ones they had were so inaccurate as to only give you an "about" air pressure. So the method was to identify the contact patch, it works and in fact is very accurate.

Just the other day I had to replace the tires on my heavy duty rough cut mower. In talk with the guys at discount tire about my the OEM's tires that offered not as much traction as I needed in mowing the acreage I needed to mow. They suggested a agriculture small tractor tire. The tire is a size larger and has the typical tractor tread, works GREAT, but I had to adjust the pressure to get a full contact patch and I did so by the dust method.

I am quite fanatical about my tires, I watch air pressure like a hawk. When I do my walk arounds on my 5th wheel, trucks, cars, tractors first thing I look at is dirt on the contact patch, looking for any sign of under inflation. Can't tell ya how many slow leaks from an embedded nail or screws I have caught over the years...before I had an outright flat or blowout.

[Airdale]

Originally Posted by 17 Oaks

Your mixing apples and oranges. There are no Jeep Wranglers that come from the factory with 37x12.50 load range D tires, so by putting them on my '03 Jeep wrangler I way outside any parameters that Jeep OEM has for tires.

The tires that came on the vehicle and their recommended cold inflation pressures displayed on the vehicle certification label are the benchmark for all replacement tires regardless of how radical they might be. The load capacity the OE tires provided at the recommended cold inflation pressures on the placard are a minimal requirement. It's a prime example of the need of tire manufacturer load/inflation charts. A savvy tire installer will obtain the information from the vehicle certification label. Then, use a tire inflation chart for the replacement tires and set a new recommended cold inflation pressure that will provide a load capacity - via inflation pressure - equal to the OE tires. Once set, the options remain the same, all inflation pressures between the new recommended cold pressures and tire sidewall max are optional.

That said how do I calculate air pressure? Here the answer is simple, identify the contact patch, if its overinflated it will show up in the center, under on the edges, good patch is easy to identify and I gave a couple of methods I have used.

The contact patch is the vehicles connection with the surface. For street and highway use the 16 lbs worked on all 4 corners of my Jeep, for off road use I ran 3-5 lbs max.

Identifying the contact patch thru a manual means such as stated is not something I read in Cars B Us monthly mag, last week. Been doing it all my life and learned it from my dad, who had done it all his driving life going back to his first car, a Model T.

Yes, go out to my shop and you can find a large air compressor and assorted air gauges from digital to analog and I like many have the ability to add as little as a .5 lb of air if need be. But this has not been the case for a good deal of my life and certainly in my dad's time not all all. You pumped up a tire using a hand pump and few had gauges of any kind and the ones they had were so inaccurate as to only give you an "about" air pressure. So the method was to identify the contact patch, it works and in fact is very accurate.

Just the other day I had to replace the tires on my heavy duty rough cut mower. In talk with the guys at discount tire about my the OEM's tires that offered not as much traction as I needed in mowing the acreage I needed to mow. They suggested a agriculture small tractor tire. The tire is a size larger and has the typical tractor tread, works GREAT, but I had to adjust the pressure to get a full contact patch and I did so by the dust method.

I am quite fanatical about my tires, I watch air pressure like a hawk. When I do my walk arounds on my 5th wheel, trucks, cars, tractors first thing I look at is dirt on the contact patch, looking for any sign of under inflation. Can't tell ya how many slow leaks from an embedded nail or screws I have caught over the years...before I had an outright flat or blowout.

See in blue above. That's the tire industry standard procedure used for all tires used on the highway.

[17 Oaks]

Originally Posted by Airdale

See in blue above. That's the tire industry standard procedure used for all tires used on the highway.

I am not sure where they get this magic tire inflation chart, because it would be a different chart for every tire, nor have I ever seen one.

Not to say that is could not be done as you stated, but there would a lot more needed than just looking at a chart.

That said my method, tried and true for almost a 100 years WORKS because the bottom line is its all about the contact patch and I am not sure you understand that.

My Jeep weighed in at about 4800 in off road trim (I forget the exact weight) but very close and it weighed the same at every wheel within 25 lbs. Now there are NO Jeep Wranglers that come from the factory even close to that weight. Most of that weight was in add on 'armor plate, then my tool spare fuel, water, passenger etc. The tires and wheel tipped the scales at about 111 lbs each IIRC.

My 37x12.50 BFG KM2 Load range D was good for 3525 lbs @ 50 psi. At that psi I have have been riding on the center of the tread only, at 16 lbs I got full and proper contact patch.

This is my Jeep with most of the weight on the rear, tires at 3 psi, note the rear tires.




Take away: If want you want to know if you have the proper contact patch the only way is to visually see it. And it only take a few lbs +/- to be running high center or rolling over outer edges. Sure if you keep your vehicle 100% OEM, I see no need to identify the contact patch, but if you run over size tires, or if load the vehicle up unless you got a weight scale in your back yard you don't know have much you have loaded.

How do you think the tire mfg determine max weight/max load...they look at the contact patch that is created as weight is applied at the max inflation pressure for that specific tire. Charts do not know how your vehicle is outfitted!

If you go outside the OEM parameters safety is your number one concern, a vheicle that does not have the proper inflation for the weight of the vheicle is a danger to all on the road

There are charts that give added psi for added weight, here is just one:

[Airdale]

Originally Posted by 17 Oaks

I am not sure where they get this magic tire inflation chart, because it would be a different chart for every tire, nor have I ever seen one.

Not to say that is could not be done as you stated, but there would a lot more needed than just looking at a chart.

That said my method, tried and true for almost a 100 years WORKS because the bottom line is its all about the contact patch and I am not sure you understand that.

My Jeep weighed in at about 4800 in off road trim (I forget the exact weight) but very close and it weighed the same at every wheel within 25 lbs. Now there are NO Jeep Wranglers that come from the factory even close to that weight. Most of that weight was in add on 'armor plate, then my tool spare fuel, water, passenger etc. The tires and wheel tipped the scales at about 111 lbs each IIRC.

My 37x12.50 BFG KM2 Load range D was good for 3525 lbs @ 50 psi. At that psi I have have been riding on the center of the tread only, at 16 lbs I got full and proper contact patch.

This is my Jeep with most of the weight on the rear, tires at 3 psi, note the rear tires.




Take away: If want you want to know if you have the proper contact patch the only way is to visually see it. And it only take a few lbs +/- to be running high center or rolling over outer edges. Sure if you keep your vehicle 100% OEM, I see no need to identify the contact patch, but if you run over size tires, or if load the vehicle up unless you got a weight scale in your back yard you don't know have much you have loaded.

How do you think the tire mfg determine max weight/max load...they look at the contact patch that is created as weight is applied at the max inflation pressure for that specific tire. Charts do not know how your vehicle is outfitted!

If you go outside the OEM parameters safety is your number one concern, a vheicle that does not have the proper inflation for the weight of the vheicle is a danger to all on the road

There are charts that give added psi for added weight, here is just one:

Tire load inflation charts are standardized by size, not brand. The chart below has a lot of really good tire industry standards about the charts and their usage. Your current size is listed in this chart.

https://www.toyotires.com/media/2125...s_20170203.pdf