Maximum speed

[Action]

Originally Posted by TRIPPPIN

........ The sidewall of this tire is strong but we do stress the sidewall when parking, tight turns etc. Since we stress them for literally minutes at a time and 99% of the time we are going in a straight line is interply shear a concern for this tire at these lower pressures? Inflating to the max pressure is just to hard on the trailer.

Going in a straight line on a smooth road surface with zero changes in road elevation - no additional stress or flex induced by the surface the tire is running on. Just flex from the rolling tire.

However the road surface I described does not exist. As a result the suspended towed load shifts from front to back and side to side transmitting stresses to the tires. Since the tires are in the center of the trailer, tire flexing becomes greater bcause of load leverage from the ends of the trailer. Have this motion occur at speed and the force transmitted back to the contact with the ground (tire) become high. Repeat several hundred thousand times because you like to go camping and the tires are working hard to stay glued together.

>>>>>>>>>>>>Action

[Barbieri]

If a tire is designed to carry 2830 lbs at 80psi, and it's on the sidewall. It's telling me that is the max weight I can carry per tire. If I under inflate a tire do I know at that moment what weight I am carrying in the trailer. In all probability I won't know. So for safety sake I fill to max. Years ago that information wasn't on the tire now it is. So if you deviate from that information the liability is on your shoulders. Remember firestone. That was because people don't pay attention to the pressure in their tires. I see it everyday.besides it's my understanding that people are not supposed to be riding in the trailer.

[Action]

Barbieri

No one is suggesting a smooth ride for passengers. It is designed for a smooth ride for the long term health of the trailer.

The running gear of the Airstream trailers was altered in the early 1960s and refined a couple of times in the following years. This was done to provide the smoothest ride possible due to the construction of the trailer.

The trailer is not constructed as a body on frame trailer rather a monocoque design where the exterior body is part of the structural system. This design also saves some weight. The down side is this design can not handle repeated shock loads over longer periods of time.

So the rubber torsion axle was employed along with shocks to dampen the shock loads to the structural system of the trailer. Tires and inflation of the tires become integral to that design as well. Tire inflation is like Goldilocks, too little and tire wear and handling are an issue. Too much and the handling may be an issue again however greater shock loads can be transmitted to the trailer.

While we would all like to set it and forget it, it isn't that easy. Understanding what load you have and matching the inflation to that load starts with the trailer manufacturer's recommendations and then adjusting from there. Along with monitoring the inflation pressure each morning of the tow. While max inflation may be the correct setting. Always setting max pressure under all circumstances on all trailers isn't the best for all trailers.

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[Tireman9]

Action
It is important to remember that in trailer application lower inflation means more than faster tire wear. It also results in greater shear forces in the tire structure. In multi axle trailers the Interply Shear can be 24% higher than an identically loaded and inflated tore on the tow vehicle. This is due to the fact that trailer tires are always being dragged around corners and turns. This dragging results in Higher shear at the belt edges which translates to faster (earlier) crack initiation and faster crack growth internal tot he structure.
Once the cracks grow sufficient large a belt separation can occur.

This is a MAJOR reason that tires in trailer application do not last as long as tires on motorized vehicles.

So ride smoothness vs tire durability is a trade off that you control with tire inflation. Assuming you know (have scale readings) for the actual individual tire loads and know the minimum inflation needed to support that load and ALWAYS run that pressure you will get the best ride but at the cost of shortest tire life.

[Action]

Good to know.

And my point was filling to max side wall pressure no matter application isn't a best practice. With that said many trailer manufacturers install tires that are barely acceptable for load capacity. Which means keeping max air pressure in the tire would have to be the best modus operandi.

>>>>>>>>Action

[Castaway]

Originally Posted by FCStreamer

Well, they can try to run me over, but I'm not exceeding 65mph no matter what. If I need to go faster, I shouldn't be towing 8000 lbs.

I totally agree

[Barbieri]

Sorry but the last paragraph has me scratching my head.try this on and see if you agree. While what you said about AS suspension is correct. The part about the tires is not and that is where I disagree with you.

I call it the Brady effect.
I am a tire designed to carry 2830 lbs at 80psi at max speed of 80 mph. While I don't drive at that speed it's possible for me to go that fast. When I was first mounted to the trailer I was filled to 80psi. The trailer was loaded but during the night the ambient temperature dropped to 60 and the psi went to 71. In the morning the psi of the tire being warmed by the sun was 73 psi. Going on the road both tires being effected by friction went to 80. After a while this went to 85 psi. All things being equal I had not loaded the trailer to max. I was probably 500 lbs less than max. I empty both gray and black water tanks and carry about 15 gallons of fresh water. Since I am at 80 psi the side walls don't flex and it also is a margin of safety.
The 80 psi is on the sidewall and I always maintain that pressure. It's what I call safety and since I don't have scales to check trailer weight and I consider it my margin of safety. I know the trailer is not fully loaded so the tires without removing air pressure can handle. If you lower the tire pressure you increase the flexing of the sidewalks and increase the friction.
You remember the football fiasco. Well the footballs were inflated in the locker room that was probably 73 or so degrees warm. Taken outside the psi of the footballs dropped and people thought they were cheating. I guess in school they missed the part in science that said warm air expands and cold air contracts. In short The Brady effect. (I made it up).
I believe that tires are developed with all possibilities in their construction. I drive with 80 psi.

[Barbieri]

This is the weight information posted in my trailer. I have managed overtime to remove almost 500 lbs of weight.

[Tireman9]

Originally Posted by Action

Good to know.

And my point was filling to max side wall pressure no matter application isn't a best practice. With that said many trailer manufacturers install tires that are barely acceptable for load capacity. Which means keeping max air pressure in the tire would have to be the best modus operandi.

>>>>>>>>Action

Well in my professional opinion the best practice when it comes to tires is to do the best you can to keep to keep the internal structural forces as low as possible so microscopic cracks are not formed and if they are formed you try and keep them from growing to the point that the tire comes apart. Failing that you need to either plan on replacing at 3 years or shorter or to have them dismounted and inspected by a professional forensic engineer.

To do otherwise means you are playing craps with the safety of your RV and with the safety of those around you as you drive down the highway.

[Tireman9]

Originally Posted by Barbieri

Sorry but the last paragraph has me scratching my head.try this on and see if you agree. While what you said about AS suspension is correct. The part about the tires is not and that is where I disagree with you.

I call it the Brady effect.
I am a tire designed to carry 2830 lbs at 80psi at max speed of 80 mph. While I don't drive at that speed it's possible for me to go that fast. When I was first mounted to the trailer I was filled to 80psi. The trailer was loaded but during the night the ambient temperature dropped to 60 and the psi went to 71. In the morning the psi of the tire being warmed by the sun was 73 psi. Going on the road both tires being effected by friction went to 80. After a while this went to 85 psi. All things being equal I had not loaded the trailer to max. I was probably 500 lbs less than max. I empty both gray and black water tanks and carry about 15 gallons of fresh water. Since I am at 80 psi the side walls don't flex and it also is a margin of safety.
The 80 psi is on the sidewall and I always maintain that pressure. It's what I call safety and since I don't have scales to check trailer weight and I consider it my margin of safety. I know the trailer is not fully loaded so the tires without removing air pressure can handle. If you lower the tire pressure you increase the flexing of the sidewalks and increase the friction.
You remember the football fiasco. Well the footballs were inflated in the locker room that was probably 73 or so degrees warm. Taken outside the psi of the footballs dropped and people thought they were cheating. I guess in school they missed the part in science that said warm air expands and cold air contracts. In short The Brady effect. (I made it up).
I believe that tires are developed with all possibilities in their construction. I drive with 80 psi.

The increase in Interply Shear is not unique to AS as tires on any trailer without an "active steering feature" will force the tires to slide around every turn or corner as the tires can not rotate around a center-line that goes through the center of the turn radius.

The slip angle and cornering forces translate into high Interply Shear forces which are concentrated at the belt edges. When those forces exceed the strength and elastic limit of the rubber belt skim cracks form at the molecular level and once formed never get smaller but always get larger. Sometimes even growing when there is no cornering as simply rotating under load can cause the cracks to grow.

In your example the temperature would have had to drop from about 130F to see that much loss in pressure. Yes if you ever travel in areas of extreme temperature swings you will need to make adjustments to both travel speed and to monitor tire inflation closely.

Pressure variation due to running are accounted for in tire design. In fact it could be said that the pressure increase is expected and even desired so if you do something like starting with low inflation you will be doing damage tot he tire structure.

RE tire max speed. In your theoretical example of 80 mph (which does not exist) you need to remember that all that is required to receive a speed rating is for a new tire to run for 30 minutes at the max speed level and not have external visible signs of failure. There is no requirement in the testing for a tire to have no internal structural failure or for the tire to be able to run even 50 miles at 50 mph after the high speed run.

Tires are designed with many possible uses in mind but not all possibilities and certainly not to be run in overload, underinflated or excess speed for the life of their tread wear.

[Barbieri]

Sorry but we don't have 130 here in Texas and yes it did drop as noted. That according to my tpms and digital gauge. Both on the mark. And yes I do notice the stress placed on tires especially when backing into an rv slot. Sorry but I am only quoting from an email I received from a tire manufacturer and he stated 81 mph. I saved the email. I did at one time hit 75 mph. It was only for a few minutes. Hitting 80 would not be a problem for my setup, but I choose not to.

[slowmover]

Originally Posted by Tireman9

The increase in Interply Shear is not unique to AS as tires on any trailer without an "active steering feature" will force the tires to slide around every turn or corner as the tires can not rotate around a center-line that goes through the center of the turn radius.

The slip angle and cornering forces translate into high Interply Shear forces which are concentrated at the belt edges. When those forces exceed the strength and elastic limit of the rubber belt skim cracks form at the molecular level and once formed never get smaller but always get larger. Sometimes even growing when there is no cornering as simply rotating under load can cause the cracks to grow.

In your example the temperature would have had to drop from about 130F to see that much loss in pressure. Yes if you ever travel in areas of extreme temperature swings you will need to make adjustments to both travel speed and to monitor tire inflation closely.

Pressure variation due to running are accounted for in tire design. In fact it could be said that the pressure increase is expected and even desired so if you do something like starting with low inflation you will be doing damage tot he tire structure.

RE tire max speed. In your theoretical example of 80 mph (which does not exist) you need to remember that all that is required to receive a speed rating is for a new tire to run for 30 minutes at the max speed level and not have external visible signs of failure. There is no requirement in the testing for a tire to have no internal structural failure or for the tire to be able to run even 50 miles at 50 mph after the high speed run.

Tires are designed with many possible uses in mind but not all possibilities and certainly not to be run in overload, underinflated or excess speed for the life of their tread wear.

I know youve repeated yourself on this subject, but I found this very well said. Thx