Chris wrote:
.........Maybe it is time to test ST tires to the same standards that LT tires are required to meet?
Chris
I think you will find that even with all those issues mentioned, ST tires will still pass the standard. Perhaps the following will help explain.
There is a industry standard tire test called "Step Load" (or Step up Load) - and it was that test that was adopted by NHTSA for there regulation - and it goes something like this:
A tire is mounted and inflated to the rated pressure and loaded against a wheel. The test starts at - and I hope you'll forgive me if I don't get this exactly right - 90% of the rated load. The tire is run for 2 hours, then the load is increased by 5% of the rated load and run for another 2 hours. This is reapeated again and the tire passes if it hasn't failed to complete the 100% load step.
In order to assure that EVERY tire passes the test, it is common for tire manufacturers to continue the test by additional steps - and then set a minimum, but elevated, level over the required test load.
So let's say that experience has told a tire manufacturer that they need a minimum of a 130% (30% overload) for LT type tires. If they were to test an ST type tire of the same exact construction, the difference in load between an ST and an LT is about 12% - so every ST tire would also pass the test - at least from the point of view of satisfying the regulation.
Now let's talk about failure rates. Tire manufacturers get tires returned under their warranty provisions. Since they know how many were produced, they can figure out a rate of failure vs time - and obviously, the older a tire is, the more likely it is to fail. If the tire manufactuer has a good handle on the return pattern, it only takes a small bit of time before they can predict the rest of the curve.
The problem here is that folks like ourselves who only see what is immediately around us, can't gauge how big the problem is. To put this in perspective, try googling ANY tire manufacturer and you will see LOTS of reports of failure. Considering that there are about 900 MILLION Passenger Car and Light Truck tires in use in the US at any particular point in time, I think it is easy to see that statistics is going to dictate that these would be visible even if the failure rate is 1 in a million.
BTW, tire manufacturers are required to report their warranty returns to NHTSA. That's why it is important for folks to file a report with NHTSA when these things happen. That is a way for NHTSA to determine if what data they are recieving matches what is going on in the real world.
