Here is my take on the XPS Rib in trailer service based on what I have learned here. As an introduction to my conclusion, I need to set up a hypothetic situation, so bear with me.
I decide to form a tire company -- ERS Tire and Rubber Company Limited. My thoughts behind this are that people going out into the woods with their trucks to gather firewood just don't have an appropriate tire for their trucks. So I have found a niche market. Chris is my marketing manager. After some discussion with him, we decide our introductory tire will be an LT235/75R16 Load Range E. Now if we run the numbers through the load formula, we know even before we start designing this tire, its load rating will be 3042 pounds at 80 psi when used in a single wheel application. I have already located a factory in Brazil that will build our tires. They can build them within our design parameters plus or minus 6 percent.
Now Chris and I go talk to our engineers -- Roger (whom we have hired out of retirement) and Barry (whom we have hired away from the company he is working for now). We start discussing the design criteria. What Chris' research shows is the current market offerings don't fill the need because they simply won't take the abuse these guys put their trucks through gathering firewood. They overload them, drive over tree stumps, spin their wheels going up steep gravel roads, and drive too fast on the highway given the load they have.
Now if I understand our engineers, we could design a tire to 108% of the specs, and given the plus or minus 6% of our factory, every tire we build will meet the specs as stated and molded into the sidewall. But Chris, Roger, and Barry informs me that I will end up with a tire that just won't fill the niche we are after because it won't take the abuse these firewood collecters inflict on tires. Barry informs me that he and Roger can design a tire that will meet the specs to 172%, but it is going to cost more than the other tires currently on the market. Chris' market research indicates the market is such that they would pay the higher price for a tire that we take the abuse they dish out. So we design the tire to 172%, manufacture some, and Calvin (another guy we hired out of retirement who has experience with aircraft tires) gets us through all of the DOT testing with flying colors. Then we go through the process of mass production and sales.
So what happens if a guy doesn't collect firewood? He buys these tires and puts them on his truck. He can certainly load his truck up with gravel to the point the tires have 3042 pounds on them (after making sure he has 80 psi in them) and haul the gravel down the highway at 65 mph without incident. He could probably get away with putting 4200 pounds on each tire and go down the highway at 60 mph without issue, because we overbuilt the tire.
Now back to the XPS Rib. They could have built the thing to 110%. It would meet the specs and pass the DOT tests. Put them on a tandem axle trailer with 6K axles and run them at 70 mph in through West Freaking Nowhere Texas on a summer day with the trailer loaded to the max cargo carrying capacity, and you would probably end up on the side of the road changing a flat. I think Michelin was aiming for a market where the person driving the truck does not own the truck. The driver doesn't care about the truck and abuses it. There is a market for a tire that will hold up to this abuse so the truck stays in service. Enter the Michelin XPS rib. So when you put these on the 6K trailer axles and stuff the trailer with you junk to the point where you have 6400 pounds on each axle, you get the bearings a little hot, take the camber out of the axles, and break a few leafs in your springs, but you never blow out one of them ribs.
