FastEagle wrote:
No matter the type or design tire used on our trailers, they still have to have the proper air pressure to operate within it’s advertised parameters. According to a NHTSA survey, under inflation is the most abused condition found when inspecting tires used on our highways.
So let’s ask the engineers some questions. I’ll kick it off with these.What is the origin of the load inflation charts found on the internet from various tire manufacturers?....
The tire standardizing organizations: The Tire and Rim Association (TRA) for the US based tire manufacturers, ETRTO (European Tyre and Rim Technical Organization) for the European based tire manufacturers, and JATMA (Japanese Automobile Tire Manufacturers Association) for the tire manufacturers based in Japan. There are others, but those are the 3 main ones and they all consult with each other. While the standards may be slightly different, the operative word here is "slightly' - not enough to worry about.
HOWEVER, no tire manufacturer is obligated to use those standards. They can make up anything they want. There is no law that says they CAN'T. There ARE laws about some of the details - like what has to appear on the sidewall, the size of the letters, the tests that have to be passed, etc.
I hope it is obvious that deviating from TRA, ETRTO, JATMA, etc. carries with it a HUGE legal risk. A tire manufacturer would be well advised to either use the standards as written or get them modified. You will rarely find deviation because of that.
FastEagle wrote:
... Are they written for the public at large to apply them as they see fit?........
No.
FastEagle wrote:
........Or, are they essentially provided as a tool for vehicle manufacturers and tire installers?.......
Not tire installers. Here's how this works:
Tire manufacturers design their tires to the tire standards as published. Vehicle manufacturers select the tire size and inflation pressure based on that same standard. That size and inflation pressure info is published somewhere for use by the vehicle's operator.
For cars, light trucks, and trailers, it's published on the vehicle tire placard.
- and so everyone understands where my expertise ends, it is here. I am thoroughly familiar with cars and light trucks, and barely so with trailers. I also have extensive experience with earthmover, industrial, and mining equipment, but medium trucks is an area I have't explored much. So some of what I post may be off the mark a bit.
BUT - For medium trucks, the weights of the vehicles are highly regulated, so the tire loads are published by the vehicle manufactirers and the trucking companies work with the tire manufacturers to select appropriate tires.
So for cars and pickup trucks, the vehicle tire placard tells both the consumer and the tire dealer, enough information to properly size and inflate the tires. The same applies to RV trailer - EXCEPT _ there appears to be a problem - which is the point of these discussions.
FastEagle wrote:
.......We see lots of information about getting our trailer’s to the scales and getting each tire position weighed. Then we are told to air the tires to the highest weight on each axle as long as it’s within the tires operating parameters. Isn’t that being counter productive? Doing that provides zero load capacity reserves for the heavy tire. Besides that, the procedure may not apply to all trailers because, we are already told by the vehicle manufacturer to air our tires to the maximum allowed via the tire placard.
FastEagle
I see 3 problems:
1) The sources of these recommendations are different.
2) Some of these recommendations are based on the situation at hand - a vehicle with a specified tire size and Load Range. That really limits what can be said.
3) There is the political situation. The vehicle manufacturers buy from tire manufacturers - and vehicle manufacturers can be pretty demanding. Tire manufacturers are incredibly reluctant to contradict vehicle manufacturers for fear of losing business.
Then there is the issue of WHO is responsible if there is a tire failure. Unless there is a documented overload situation, then the vehicle manufacturer washes his hands of the situation, so by default it becomes the tire manufacturer's. (Editorial note: I am sure my prejudice is showing.)
On the surface it appears that RV trailer manufacturers select their tires so they are barely within the loading parameters - so when the tire manufacturers say follow the pressure listed on the tire's sidewall, they are making the best of the situation.
Weighing trailers? That's supposed to detect when the tires are overloaded. Apparently, this is pretty common occurance - although I don't have firsthand knowledge.
Remember when I said that tire manufacturers are reluctant to contradict vehicle manufacturers? The recommendation to weigh the trailer is a way of determining when the vehicle manufacturer hasn't done his job properly - without the fear of reprisal.
Reserve tire capacity? This again goes back to the business of contradicting the vehicle manufacturer. Unlike General Motors, or Ford, or Peterbilt, RV manufacturers don't buy tires in such large volumes. Plus individually, they are such small potatoes they don't merit attention. As evidence of this, I point to NHTSA which pays very little attention to the RV market.
Besides, airing the tires up to the sidewall maximum is basically what is on the vehicle placard, so there is no contradiction there.
And my last thought: Roger and I both are working outside the business system - and that gives us a certain amount of manuevering room that doesn't exist with official publications. You will find us - well - not exactly contradicting what is published, but offering advice that you probably won't get from vehicle manufacturers or tire manufacturers. That advice is based on our experience in how tires work.
