DOT Endurance Test for ST Tires NOT same for LT Tires

[Timmo_]

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?SID=aba3fbd2309d865cce127033c4dbd2d0&mc=true&node=se49.6.571_1...

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?SID=aba3fbd2309d865cce127033c4dbd2d0&mc=true&node=se49.6.571_1...

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)



LT Tire Endurance Test (excerpt)


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]

Time for this one to go to sleep. Thread closed.
Barney

[Timmo_]

Grit dog wrote:
Not unlike alot of topics, many of the posts or arguments are quite inane when one categorizes all sizes and load ratings of tires into 1 blanket statement.
Case in point, the OPs assertion in his previous thread, that because he has one application where he can use a LT tire in place of a ST tire and because that tire is apparently suitable for that load and performs well in his opinion, that LT tires are better and ST tires are not good (even if you can’t buy a LT tire for your particular application).


But keep up the broad generalities. No need to introduce good or specific information to get in the way of a good ole argument about essentially nothing!

Grit, this is getting silly. I never said, "LT tires are better and ST tires are not good."

I shared my personal experiences that replacing my ST Marathon tires with LT Wrangler tires provided me with 900 pounds in additional tire capacity (period).

You were the one that said, "Available ST tires far exceed the capacity of 14" and 15" "LT" tires"...and offered no examples.

[fj12ryder]

I keep hearing about the ST tires having stronger sidewalls. That is a bunch of hooey. I've checked the ST tires that came off my toyhauler, and the sidewalls were like tissue paper. No way can they be called robust. Very, very flexible. More flex, more heat, more heat, more failures.

[StirCrazy]

ktmrfs wrote:

StirCrazy wrote:
one thing people fforget is ST tires were designed to handle the torsional stresses that are put on a trailer when you are cranking it sideways into a parking spot. LT may very well be great for going down the road but they dont handle the twisting stresses as good as ST tires.

Steve

It may very well be true that an ST tire handles torsional load much better than an old 2ply or 4ply passenger car tire that existed when ST tires first started appearing and may be better than a P rated tire today. But saying a LT tire is not capable of handling the same torsional load as an ST is IMHO stretching it.

LT tires are not some new magical thing, I have been running them for 40 years. yes they are better than P tires because they are designed to handle more weight, but the simple thing is that LT tires are desgined with traction and ride quality in mind, so generaly for the same size a ST tire will carry more, and get better fuel milage and handle the sidewall stuning streasses better as they have a more robust sidewall since there not worried about ride quality. but if you insiste on driving real fast with your big trailer I guess you need LT tires.

Steve

[StirCrazy]

Lynnmor wrote:

StirCrazy wrote:
one thing people fforget is ST tires were designed to handle the torsional stresses that are put on a trailer when you are cranking it sideways into a parking spot. LT may very well be great for going down the road but they dont handle the twisting stresses as good as ST tires.

Steve

I guess steering 10 tons while applying considerable torque and horsepower on a sharp mountain curve has little effect on a tire?

actualy not even close. have you ever watched your tires while jack knifing the rv into a spot, they are almost folded out oposit from each other. a curve on the highway you are barley turning the wheel so the stresses are totaly different.

Steve

[ktmrfs]

StirCrazy wrote:
one thing people fforget is ST tires were designed to handle the torsional stresses that are put on a trailer when you are cranking it sideways into a parking spot. LT may very well be great for going down the road but they dont handle the twisting stresses as good as ST tires.

Steve

It may very well be true that an ST tire handles torsional load much better than an old 2ply or 4ply passenger car tire that existed when ST tires first started appearing and may be better than a P rated tire today. But saying a LT tire is not capable of handling the same torsional load as an ST is IMHO stretching it.

[Grit_dog]

Not unlike alot of topics, many of the posts or arguments are quite inane when one categorizes all sizes and load ratings of tires into 1 blanket statement.
Case in point, the OPs assertion in his previous thread, that because he has one application where he can use a LT tire in place of a ST tire and because that tire is apparently suitable for that load and performs well in his opinion, that LT tires are better and ST tires are not good (even if you can’t buy a LT tire for your particular application).


But keep up the broad generalities. No need to introduce good or specific information to get in the way of a good ole argument about essentially nothing!

[JIMNLIN]

LT may very well be great for going down the road but they dont handle the twisting stresses as good as ST tires.

This comes under fake news.....or ST tire propaganda perpetuated for years by Carlisle tire adds and later on by tire chain stores especially Discount Tire stores and newb trailering bloggers.
Ever watch a Ford truck with the old solid front axle make a sharp steer around a corner with the tire roll over on the outside edge of the tread.
Like Barney mentioned in the first reply is ST tires were designed for trailer use only.
I've noticed this leads some to the mis assumption that some how they were superior in certain performance to LT tires.

[Lynnmor]

StirCrazy wrote:
one thing people fforget is ST tires were designed to handle the torsional stresses that are put on a trailer when you are cranking it sideways into a parking spot. LT may very well be great for going down the road but they dont handle the twisting stresses as good as ST tires.

Steve

I guess steering 10 tons while applying considerable torque and horsepower on a sharp mountain curve has little effect on a tire?

[StirCrazy]

one thing people fforget is ST tires were designed to handle the torsional stresses that are put on a trailer when you are cranking it sideways into a parking spot. LT may very well be great for going down the road but they dont handle the twisting stresses as good as ST tires.

Steve

[Timmo_]

Jim, I went with Wrangler HT215/75R15--and those tires provided me with nearly 1000 pounds of load capacity (over Marathons).

From the other thread---

Timmo! wrote:

Grit dog wrote:

Timmo! wrote:
I second the emotion---Goodyear Wrangler LT tires

This is not sound advice unless the OP's trailer has 16" or larger wheels, which it most likely doesn't, since it's a TT.
Available ST tires far exceed the capacity of 14" and 15" "LT" tires.

Whoooa Nelly...."not sound advice"? "far exceed capacity"? Let's not exaggerate. A tire that has 2.6% greater load capacity--isn't much of an increase in load capacity (period).

Granted I replaced GY Marathon ST205/75R15 (load range C for 1870 lbs) with GY Wrangler HT215/75R15 (load range D for 2095 lbs), providing me a tire with 225 lb greater load capacity. Now my friend, increasing a tire load capacity of 225 pounds (10.6%) is rather significant

About 4 years ago, ST Marathons were replaced with ST Endurance. So, let's compare those (even though Marathons are still being sold), GY Endurance ST205/75R15 has a load range D for 2150 lbs. I agree the Endurance tire has a greater load capacity of a mere 55 lbs than HT Wrangler, but that is only a 2.6% greater load capacity. Not very much and certainly does NOT "far exceed capacity".

The Endurance has a shallow tire tread depth of 8/32" (0.25"), while the Wrangler has a deeper tire tread of 14/32 (0.4375"), has a wider width and larger diameter, and higher speed rating.

At the time of my tire purchase, the HT Wranglers were only $5 more, and well worth the extra rubber.

Gotta look at the facts.

On edit--corrected math. 2095 - 1870 = 225 lbs, not 255 lbs. My bad.

[mkirsch]

14" and 15" tires are getting hard to find period unless you want some wide low profile thing for your pretend road rally kazoo box.

Back in the day, though, LRC was more than adequate for your typical 1/2 ton pickup that would come with LT rated tires on 15" rims.

Nowadays its getting so you need minimum 16" rims if you want to go with LT tires, and even 17" or 18".

[CapriRacer]

Sjm9911 wrote:
I would say that the manufactures of the tires run there own tests and pass that info along with the results to get the ratings. Otherwise how would they come up with them? I don't think they guess. This is just the DOT testing and most likely does not represent the actual testing the tires go through by the manufacturers when they are conceived.

Allow me to confirm that tire manufacturers do their own testing, but they also do their own rating. DOT does only verification/ spot check testing. If they (DOT) find no issues, no one knows about the tests. If they (DOT) find an issue, they contact the tire manufacturer for clarification.

And just to be clear: Since we are talking about ST and LT tires, the load table is set by the tire standardizing organization - The Tire and Rim Association - and the tires are tested against that standard.

But for speed rating, there is an ATSM (SAE) test - again, conducted by the tire manufacturers for compliance to their published rating which DOT might test for compliance.

And just an FYI, for ST tires, the speed limitation for unrated tires is 65 mph, but there is no published speed limitation for unrated LT tires. Yes, this is a bit of a conundrum.

[ktmrfs]

Those could be a good option for some.

2000 capacity is VERY marginal for my trailer, The Maxxis in LRe might work will need to check them out. I need something in the 2500lb capacity to have a reasonable margin.