China Bombs Got Me

CapriRacer wrote:
JJBirish,

There are a number of items in your post I would like to comment on, but in the interest of brevity, I’ll only focus on only one – one that I think is the key difference in our understanding of the DOT testing requirements. Perhaps we can find common ground.

First, I hope it is clear that tire “size” plays a large role in the rated load of a tire regardless of tire type. Put another way, larger tires have more rated load than smaller tires – all other things being equal. In trying to compare rated loads of tires of different types, we need to also compare tires of the same “size”. I put the word “size” in quotes because the letters in front of the numbers (in my view) also are part of the “size” as they delineate the type of tire involved.

When it comes to comparing LT tires and ST tires, there is a problem – very little commonality in “size”. I’m going to chose a “size” that is common to both LT’s and ST’s – 235/85R16 Load Range E:

ST235/85R16 LR E: Max Load 3640# at 80 psi – with a speed restriction of 65 psi.

LT 235/85R16 LR E: Max Load 3042# at 80 psi – and a common speed rating is Q = 99 mph.

Notice the difference in rated loads and speed restrictions. I hope it is obvious that a tire’s speed capability is inversely related to its speed – that is, the higher the speed, the less load it is capable of carrying (all other things being equal) – and that is reflected above.

So let’s take one of the DOT required LT tests and see how that plays out as far as load goes. How about this one:

JJBIRISH wrote:
.....=================================================

Category B Endurance Test:

(LT "E" tire at 50 PSI)
4-hour test: 85% of tire maximum load rating at 75 MPH
6-hour test: 90% of tire maximum load rating at 75 MPH
24-hour test: 100% of tire maximum load rating at 75 MPH

……..

For an LT235/85R16 Load Range E, the last step is 3042# load.

But for an ST235/85R16 Load Range E, that’s only 84% of its rated load. Or put another way, it is only 110% of the maximum load at 50 psi.

I think an ST tire can survive that last step.

Comments?

Commenting about something that will never be tested or proven… I have read the arguments that the regulations don’t need upgraded for the trailer tire because they are not passenger tires in part time use and offer little in the way of risk of injury, and subsequently were dropped from new testing procedures… the fact is the trailer and tire industry lobbying along with the regulatory agency have allowed for the design of a cheaply built tire for trailer use…

As far as you assertion that the ST could pass some of the test… maybe… But I doubt the ST tire would pass that test either… sure it would only be 110% of its rated load for that psi but it would also be at 10 MPH above its maximum rated speed… the combination of the over load on a tire with no reserve and run above its maximum speed rating, with a tire that has the rounded sidewalls that are designed as a part of the trailers suspension would IMO run much hotter than the straighter sidewall LT tire with built in reserve capacity and within its rated maximum speed rating, and would fail much sooner than the LT in that test…

Also when I consider these things I have to consider what is mandated… I can’t assume the tire company is going to overbuild in my favor, or do the right thing… what I know from my own experience and a lifetime on the road for a living and for pleasure is the ST has a higher risk of failure…
since I had never had a blow out on anything but a LT tire in the light duty line, I myself didn’t believe it until I sent very much of my time researching the issue… I believe there are many reasons the risk of tire failure is higher for RV’ but the tire type is right at the top of the list…
Now that almost all ST tire mfg. has moved to mainland China I have even more reason for concern…

Sorry about the delay but my wireless internet is so poor I can go for days without any service and when I do have it, it is slower than dialup and RV.net especially don’t work then…