Chris wrote:
FastEagle wrote:
FastEagle wrote:
As an example, the ST235/80R16E can be found with three different load capacities at 80 psi, 3420”, 3500# and 3520# depending on the manufacturer.
Here is how the DOT has worded the regulation that allows that to happen: “If the maximum load rating for a particular tire size is shown in more than one of the publications described in S4, each tire of that size designation shall have a maximum load rating that is not less than the published maximum load rating, or if there are differing maximum load ratings for the same tire size designation, not less then the lowest published maximum load rating.”
FastEagle
Just as you think you have it all figured out along comes a new item. This manufacturer has set their ST235/80R16E tire's load capacity at 3525 @ 80 psi.
Radar Angler RST21
FE
snip
Let me ask a question if you and the engineers recommend using a ST that has 115 percent of ones capacity requirement, does that mean the the higher ratings of ST tired are not realistic? Chris
My opinion on the alternate load ratings above 3,420# would be a bit suspect.
If the tires meet TRA dimensions then the air volume does not change. Since load capacity is a function of air volume which is based on many decades of real life testing and usage experience, I do not know how you can claim your tire will carry more load unless you make some other change like a meaningful reduction in tread depth which will lower operating temperature.
The other option would be a further reduction in max speed capability from the normal ST limit of 65 mph to the 62 mph we see on most of the 215/75R17.5 commercial tires.
Such a design change is really just "gaming" the system. I might be tempted to suggest that some manufacturers possibly are betting that they will be able to stay under the NHTSA radar as so few RV owners ever bother to file sufficently accurate or complete complaints to rise to the level of any action ever being taken.
Does this mean that the higher rated tires will all fail? No, I would believe that as many owners don't put enough miles on so that the cumulative damage that occurs during the short warrantee period is sufficient to result in a non-road hazard related failure. And if there are failures you simply give the RV owner a new set of tires and a few bucks and no information goes to NHTSA.
Normal production variation means some tires will fail even if properly loaded. What major tire companies (MI, GY, BS) do is apply sound statistical methods to try and keep the expected failure rate well below 1% if the tire is properly maintained. Now if you are a smaller volume mfg you have much lower exposure and you can simply change the tire name every few years so even if you have a failure rate that is 10 times or even 40 times the rate seen from one of the majors, the total number still keeps you below the radar.
The biggest problem is that some RV mfg will use these "up-rated" tires so they can claim more load capacity but the information that you need to get these specific brand tires 5 years later to meet that theoretical load capacity is somehow lost so the 2nd set is bought just on size and now the RV is running overloaded.
My recent
post on how to select a tire brand takes this "gaming" into consideration.
