Pressure

[mlpeloquin]

The proper pressure is based on maximum load rating of your trailer. Fully load it up and get it weighed. Then get the load/pressure chart for your tires. Set the pressure of the tires based on how much weight is on them plus five psi or max psi. Never exceed the max psi.

[RVPioneer]

Originally Posted by Tireman9

The charts show the MINIMUM inflation for a series of loads. The charts also show the MAXIMUM inflation for each given Load Range.


Do you understand my post on Interply Shear?

Do you understand that I asked you a question? I’ll try again.

Is it absolutely imperative that all ST tires MUST, in all cases, be inflated to the maximum pressure indicated on the side wall?

[djbckr]

Originally Posted by Tireman9

Sorry, that is an over-simplification of a tire's response to inflation. It implies that if you inflate a tire by say 5 psi over the minimum inflation needed to support a given load you will soon have a failure due to impact break.
This just isn't what happens.
Yes if you significantly over inflate a tire it may be more prone to impact damage but the level of "overinflation" is more than 5% or 10% and may be more like 30% or 50% overinflated before impacts become a serious problem. We are no talking about bias tires anymore. They were and are more suseptable to impacts than radials IMO.

I think you missed my statement about properly inflated tires. What made you think I suggested over inflating was a good thing?

[Tireman9]

Originally Posted by RVPioneer

Do you understand that I asked you a question? I’ll try again.

Is it absolutely imperative that all ST tires MUST, in all cases, be inflated to the maximum pressure indicated on the side wall?

I am uncomfortable with your use of absolutes.


I do trust the science of tire structural forces. Higher forces will probably result in a shorter life and lower forces will probably result in longer life.


The Interply Shear is indicated to be 24% higher for tires in multi-axle trailer application. You can lower, but not eliminate the Interply Shear by either lowering the load on the tires or increasing inflation. Decreasing the load is not a good option as many feel they need all the stuff they carry.
We can increase the inflation to the tire sidewall max which will lower the Interply Shear.


This last option seems to be the best. But it's not mandatory. I do not have the authority to require people to follow my recommendations.

[sirtate]

Originally Posted by Tireman9

I am uncomfortable with your use of absolutes.


I do trust the science of tire structural forces. Higher forces will probably result in a shorter life and lower forces will probably result in longer life.


The Interply Shear is indicated to be 24% higher for tires in multi-axle trailer application. You can lower, but not eliminate the Interply Shear by either lowering the load on the tires or increasing inflation. Decreasing the load is not a good option as many feel they need all the stuff they carry.
We can increase the inflation to the tire sidewall max which will lower the Interply Shear.


This last option seems to be the best. But it's not mandatory. I do not have the authority to require people to follow my recommendations.

I agree...

The only drawback of running tires at max sidewall pressure is a firmer, noisier ride....

It may shake the cupboards loose 1 season earlier than not... (Although a blowout would shake a lot more!)

[Tireman9]

Originally Posted by djbckr

I think you missed my statement about properly inflated tires. What made you think I suggested over inflating was a good thing?

Sorry, We are not communicating. I misread your Low inflation= Bad Overinflation=bad to imply that inflating a tire to more than what is needed to support the load could lead to impact failure and was bad.


Inflation below what is needed to support the load will increase the tire operating temperature which is bad for long term durability. This does not mean if you are 5 psi low the tire is definitely going to fail next week, month or year. Too many other variables.



Inflation above what is needed to support the load can increase the potential for impact damage, but the potential will vary with the level of increased inflation along with a good number of other variables such as load, speed, and ambient temperature.


I do understand people would like precise answers so they can get better tire life but life just doesn't work that way. The best we can do is offer statements such as. 'It would be better if you........."
This applies to vehicle load, speed, and inflation along with a few other items.


I have suggested people have a minimum of 10% reserve load but 15% is better and 25% is better yet but probably not achievable for most RVs.


Keeping speed below 75 is recommended in RV use by the major tire companies. ST type tires load formula is based on 65 mph max and I suggest 60 would be better from a tire life standpoint.


The list goes on.

[T12]

In my last post I said that there is a simple way to determine if your tires are over or under inflated. Buy a tire tread gauge and keep an eye on how the tires are wearing. If your tires are wearing even from one side all the way across to the other then they are properly inflated. So the answer to the question should a certain tire be run at max inflation all the time is no. I have a friend who put 10 ply tires on his truck so he could pull his tt occasionally. The tire dealer put 80 pounds of pressure in them. He took it to the dealer for service and they lowered the pressure in the tires to 32 pounds. He wasn't pulling his tt at the time. So how do you know if your tires are carrying more or less weight than they are designed for? Take your rig to a truck scale. CAT scales at a lot of truck stop have multiple segments which make the process a lot easier. Let's say you have tt that scales out at 6000 pounds and you have 4 tires. Divide 6000 by 4 and you would be at 1500 pounds a tire. If that exceeds your max tire weight your asking for trouble. If for example it was only a quarter of the max weight, the max inflation is not advisable unless you just like buying tires more often.

[Tireman9]

Originally Posted by T12

In my last post I said that there is a simple way to determine if your tires are over or under inflated. Buy a tire tread gauge and keep an eye on how the tires are wearing. If your tires are wearing even from one side all the way across to the other then they are properly inflated. So the answer to the question should a certain tire be run at max inflation all the time is no. I have a friend who put 10 ply tires on his truck so he could pull his tt occasionally. The tire dealer put 80 pounds of pressure in them. He took it to the dealer for service and they lowered the pressure in the tires to 32 pounds. He wasn't pulling his tt at the time. So how do you know if your tires are carrying more or less weight than they are designed for? Take your rig to a truck scale. CAT scales at a lot of truck stop have multiple segments which make the process a lot easier. Let's say you have tt that scales out at 6000 pounds and you have 4 tires. Divide 6000 by 4 and you would be at 1500 pounds a tire. If that exceeds your max tire weight your asking for trouble. If for example it was only a quarter of the max weight, the max inflation is not advisable unless you just like buying tires more often.

Yes, scale readings and tread wear can be an indicator of the tire's ability to support a load. What is missing is the unique and high belt Interply Shear loads due to the tires being dragged rather than steered around corners.

THIS post and image may help explain the problem better.

The bottom line is that there is a reason tires in trailer application do not last as long as when placed on a regular vehicle. High Interply Shear is the main reason for belt separations in tires on trailer usage.

Can you run less than the tire sidewall pressure? Yes sometimes if you do not exceed the load capacity for the inflation you use, but that fails to take into account these special belt forces.

[RVPioneer]

Originally Posted by Tireman9

Yes, scale readings and tread wear can be an indicator of the tire's ability to support a load. What is missing is the unique and high belt Interply Shear loads due to the tires being dragged rather than steered around corners.

THIS post and image may help explain the problem better.

The bottom line is that there is a reason tires in trailer application do not last as long as when placed on a regular vehicle. High Interply Shear is the main reason for belt separations in tires on trailer usage.

Can you run less than the tire sidewall pressure? Yes sometimes if you do not exceed the load capacity for the inflation you use, but that fails to take into account these special belt forces.

The information you’ve provided above and in previous posts provides a satisfactory answer to my question in regards to inflating ST tires to their maximum rated pressure.

It confirms my claim that the statement “All ST tires must be inflated to maximum pressure” has been shown to be incorrect. While we lack a technical document that shows the above quoted statement to be incorrect, we have load/inflation charts that provide the consumer with a range of tire pressures in which the manufacturer/tire industry has determined it is safe to operate the tires. We also have your words, as an expert, that running max pressure is a recommendation, not a must.

Certainly ST tires are a different animal and are subject to unique forces not seen in passenger vehicles. Many RV manufacturers will equip their products with the lowest cost tires that in some cases may barely be adequate to support the intended load. Many owners will overload their RV and/or fail to maintain even the minimum required tire pressure.

If, in your experience, running max pressure in ST tires adds an element of safety, I do not dispute that recommendation. I simply disagree with a statement that something must be done when that is not the case.

[Leith]

The tires on my Motor Home are rated for 120# ! I checked tire carrying capacity on web for my brand and found I didn’t need to go for max air pressure only about 100 or even a little less ! Ive been running my tires at 105 # for 5 years and everything is great ! My DP handles great and ride is good and no tire noise ! Running at max pressure gave us a harsh ride and noise ! You need to know what you RV weighs and tire carrying capacity at different pressures ! Also be aware that running tires at max pressure ratings cold that when your traveling on hot roads during the summer your tire pressure will rise and tire expands so if your at max pressure cold your stressing the tires !

[sirtate]

Originally Posted by Leith

The tires on my Motor Home are rated for 120# ! I checked tire carrying capacity on web for my brand and found I didn’t need to go for max air pressure only about 100 or even a little less ! Ive been running my tires at 105 # for 5 years and everything is great ! My DP handles great and ride is good and no tire noise ! Running at max pressure gave us a harsh ride and noise ! You need to know what you RV weighs and tire carrying capacity at different pressures ! Also be aware that running tires at max pressure ratings cold that when your traveling on hot roads during the summer your tire pressure will rise and tire expands so if your at max pressure cold your stressing the tires !

The tire designers know that tires heat up when they are used.

They also know that on hot days, they heat up even more.

If you add air to the Max. Cold Pressure rating, when the tire is COLD, you will not overstress the tire.

Yes, you may see 20psi or more above Max.Cold when running hot and heavy, but that is baked into the calculation.

Inter-belt friction causes heat in tires. When the tires flex, the belts rub against each other, generating heat.

More pressure means less flexing.

Less flexing means that the tire runs cooler.

Hot rubber fails. It's best to run the tire cooler, therefore as high a pressure that they will accept.

However, if you don't like the ride at Max. Cold, run them at the placardded pressure.

[mike5511]

I just posted basically the same answer on the other tire thread. Pulling a trailer, the ride doesn’t come in to play. I want my tires to run cool as possible. 110psi always.

[Tireman9]

Originally Posted by Leith

The tires on my Motor Home are rated for 120# ! I checked tire carrying capacity on web for my brand and found I didn’t need to go for max air pressure only about 100 or even a little less ! Ive been running my tires at 105 # for 5 years and everything is great ! My DP handles great and ride is good and no tire noise ! Running at max pressure gave us a harsh ride and noise ! You need to know what you RV weighs and tire carrying capacity at different pressures ! Also be aware that running tires at max pressure ratings cold that when your traveling on hot roads during the summer your tire pressure will rise and tire expands so if your at max pressure cold your stressing the tires !

Motorhomes and other motor vehicles i.e. not trailers can set tire pressure based on the measured tire load and get goo tire life. Please DO NOT set tire pressure planning on the pressure increase. This is definatelyNOT a proper procedure.