Good Sam Club Open Roads Forum: DOT Endurance Test for ST Tires NOT same for LT Tires
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 > DOT Endurance Test for ST Tires NOT same for LT Tires

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Timmo!

South-central Oregon...on the river

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Posted: 02/28/21 10:31am Link  |  Print  |  Notify Moderator

I believe the tire selection for one's trailer is a personal choice. Our individual personal experiences and acquired knowledge form the basis for our decisions. And I assumed (ass u me) the DOT endurance test (load capacity) for ST tires and LT tires would be the same, so I could compare apples with apples. Boy was I mistaken.

I had a conversation with a Les Schwab tire manager this past week and he enlightened me that ST Tires follow a DOT Testing requirement that has not been revised in almost 50 years (Nov 13, 1973).
https://www.ecfr.gov/cgi-bin/text-idx?SI........d0&mc=true&node=se49.6.571_1119&rgn=div8

Whereas the DOT Testing procedures for Passenger and LT tires are more rigorous and have been revised six times since Nov 18, 2002.
https://www.ecfr.gov/cgi-bin/text-idx?SI........d0&mc=true&node=se49.6.571_1139&rgn=div8

Why does this matter? ST and LT tires are tested for endurance at different speeds; ST Tires are tested at a maximum speed of 90 km/h (55 mph) while LT tires are tested at a maximum speed of 120 km/h (74.5 mph).

ST Tire Endurance Test (excerpt)
[image]
[image]

LT Tire Endurance Test (excerpt)
[image]

What does this mean?

The load capacity limit for ST Tires are not "DOT tested" at speeds above 55 mph...even if the tire has a speed rating of N (87 mph, like GY Endurance).

Does this make one tire inferior over the other? No, it just means one tire is tested at fast highway speed (74.5 mph), while the other is tested at much slower speeds (30, 50 and 55 mph).

Are we comparing two apples (Gala vs Granny Smith) or, are we comparing a Gala apple with a Naval Orange?

Does a ST tire's 2,000 lb load capacity tested at 55 mph increase or decrease when used at untested speeds of 65 mph? 75 mph?

BarneyS

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Posted: 02/28/21 11:09am Link  |  Print  |  Notify Moderator

One possible reason for the different standards between ST and LT or passenger tires is that ST's can only be used legally on a trailer and people don't ride in trailers.
You cannot, and should not, put STs on a truck or car.

The reverse does not hold true however. There is no law that I am aware of the prohibits the use of an LT tire on a trailer or car. Could be wrong on that but I have never heard of one.

Anyway, I think this is probably the main reason why ST's are not a choice for a passenger vehicle and would account for the different test standards.
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ktmrfs

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Posted: 02/28/21 01:01pm Link  |  Print  |  Notify Moderator

yes, ST hasn't been updated in a long time. and for trailer tires with only an ST rating, it is a pretty minimal test compared to car/truck tires.

However what is an open question (at least to me) is the current crop of "ST" tires like the goodyear endurance that carry a passenger car/light truck speed rating as well. To meet the speed rating requirements it seems they would need to run the endurance test at the rated speed and load like any other car/light truck tire would need to be run through for the same speed rating.

Goodyear endurance carries a speed rating for something like 85mph IIRC at full rated tire capacity.

and the chart shown by the OP doesn't show the test sequence for ST tires with a load range of C, D, or E. Or for ST tires with a speed rating of 65mph, It just starts with Load range F and speed rating of 50mph. It would be interesting to see the test sequence for ST tires with C, D, or E load range with a speed rating of 65mph like the vast majority of ST trailer tires.

It look like the chart is more aimed at tires used for mobile home tires etc.

* This post was edited 02/28/21 01:08pm by ktmrfs *


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rhagfo

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Posted: 02/28/21 02:17pm Link  |  Print  |  Notify Moderator

Well the LT tires on out 5er have a speed rating of 103 mph, and a load rating of 3,042# about 400# lower than an ST tire of the same size. Our 5er weighs about 13,000# with a little over 10,000# on the four tires. I feel better driving down the highway between 65 and 70 with the 103 mph rated LT’s than I would on ST’s speed rated for 87 mph!


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time2roll

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Posted: 02/28/21 02:26pm Link  |  Print  |  Notify Moderator

I have no doubt LT will hold up better than an ST at respective max load. At the same time I also believe an 87 mph rated ST is better than a 65 mph ST. Even if DOT runs the test at 55 mph. I don't think the DOT test is intended to be a failure test as much as a test to measure heat etc. to predict it meets the minimum standard to be on the road.


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ktmrfs

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Posted: 02/28/21 03:22pm Link  |  Print  |  Notify Moderator

I only wish there were a selection of LRD or LRE LT tires in 15" to choose from. AFAIK there is only 1 I am aware of, a 15" for sprinter vans.

LRC not an issue in 15"LT, but LRD or E another story. Now if you already have 16" rims, much easier task.

Durb

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Posted: 02/28/21 06:22pm Link  |  Print  |  Notify Moderator

My question has always been, "Why market ST tires at all if the LT tires are superior for towed trailers?" It isn't the price as Goodyear has LT tires that sell for less than Endurance ST tires.

Grit dog

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Posted: 02/28/21 07:44pm Link  |  Print  |  Notify Moderator

ktmrfs wrote:

I only wish there were a selection of LRD or LRE LT tires in 15" to choose from. AFAIK there is only 1 I am aware of, a 15" for sprinter vans.

LRC not an issue in 15"LT, but LRD or E another story. Now if you already have 16" rims, much easier task.


This was Timmos argument to begin with. He’s stuck on LT tires for smaller trailers 14-15” rims that LT tires are unavailable or all but unavailable. And of the very limited choices, they are rated much lower weight than comparable ST tires.

So bottom line, doesn’t matter what the test methods are, if you can’t buy the tire you want.


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ktmrfs

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Posted: 02/28/21 08:43pm Link  |  Print  |  Notify Moderator

Grit dog wrote:

ktmrfs wrote:

I only wish there were a selection of LRD or LRE LT tires in 15" to choose from. AFAIK there is only 1 I am aware of, a 15" for sprinter vans.

LRC not an issue in 15"LT, but LRD or E another story. Now if you already have 16" rims, much easier task.


This was Timmos argument to begin with. He’s stuck on LT tires for smaller trailers 14-15” rims that LT tires are unavailable or all but unavailable. And of the very limited choices, they are rated much lower weight than comparable ST tires.

So bottom line, doesn’t matter what the test methods are, if you can’t buy the tire you want.


what I can say is I've put almost 100K miles on two trailers, my neighbor has put close to 300K miles on two trailers he has for going to races etc. SIL folks have put 50K + miles on trailers.

All with ST tires.

Total number of tire blowouts or catastrophic failures zip, nada, zero. Between the 3 of us we have caught two nail punctures with our TPMS that likely avoided a blowout.

All three of us have run Maxxis and now goodyear endurance tires.

CapriRacer

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Posted: 03/01/21 06:08am Link  |  Print  |  Notify Moderator

As a tire engineer, I find this discussion thread very entertaining - and enlightening! Enlightening because of the misunderstanding many people have about tires and specifically ST tires.

First is that not only were the DOT tire standards not changed until 2000 (because of the Ford/Firestone situation), but one of the criticisms of the DOT at the time was that they weren't updating the standards based on what was being learned.

For example, it was obvious almost from the beginning of the DOT tire standards that the standards were not adequate to insure no tire failures (meaning not road hazard related failures!). It took nearly 40 years for the government to react - and it took a HUGE situation for there to be change.

Plus, there is still no standard on tire aging.

And don't forget, that when ST tires were introduced, many of the speed limits included travel trailers in the slower speed set for trucks.

Yup, very entertaining.

* This post was edited 03/01/21 08:58am by an administrator/moderator *


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CapriRacer

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