Forum Discussion

gmw_photos's avatar
gmw_photos
Explorer
Mar 22, 2016

75mph ST tire

I offer this only as info for the always entertaining and ongoing argument....ooops, I mean "discussion" regarding tires. I was out this morning shopping for a new horse trailer, so of course I looked down at the Chinese ST tire, and saw "75mph" on the sidewall.
I know nothing at all about these tires other than they were round and black, so this is neither a recommendation nor an indictment of them.

"Castle Rock". These were 15" load range D.

  • gmw_photos's avatar
    gmw_photos
    Explorer
    Mar 31, 2016
    rbpru wrote:
    ......snip.....

    Till then, the millions of TT and 5ver on the road will continue to roll along on STs.

    Safe travels to all.


    ....yep.

    ....and some will also be sitting at the side of the road while the driver changes a tire, praying he does not get hit by passing traffic. See the post above yours.

    EDIT: just because an industry does something a certain way, does not make it the best choice. An analogy would be millions of people smoke cigarettes every year. Many of them survive it. Many don't. The evidence certainly suggests that smoking is not a healthy thing to. do.
    Changing a tire at the side of the road can also be real unhealthy.
  • 4bearhug's avatar
    4bearhug
    Explorer
    Mar 31, 2016
    As you have found, the damages can be severe...
    But I think that there is a fourth cost as well.

    Time. My time off is precious to me. I don't want to spend it on a problem. A blowout can ruin and end a trip. That is something that I can never get back.

    Good point you make. Another reminder to everyone that RVs is to take an annual look at the spare for condition and inflation. We were fortunate that our spare was brand new, but I had not checked it since buying the 5th wheel 3 yrs ago. It was way underinflated, but useable until we could get 10-15 mi. down the road to get it properly inflated.
  • Huntindog's avatar
    Huntindog
    Explorer
    Mar 31, 2016
    4bearhug wrote:
    gmw photos wrote:
    rbpru wrote:
    If you folks are trying to say that LTs are tested to tougher standards than and ST there is no argument there. LTs are a more rubust tire because they need to be for their intended service.

    If you are trying to say the more robust testing makes them better for TT service, that is simply opinion.

    Those opinion is off set by 1.) The fact that TT and most of the other trailer industries find STs a sutable and economic tire choice. 2.) The fact that LTs are not widely used or advertized by their manufacturers for trailer service.

    People can invent a thousand reason why this is true, again just more opinions.

    My opinion is STs are used because they do what they are designed and tested to do.

    It is also my opinion that those who, go off-road, drive fast, exposed their rigs to other extremes or simply feel they need them; would best be served by a tire designed for that purpose.


    If I have to replace a $80 ST tire at 3 to 5 years, vs only having to replace a LT tire at twice that lifespan at $110, which is "more economic" ?

    Let's see, you mentioned off road. Yep, sometimes down rock roads to remote CG's. When I go to the farm to see my niece and her family, they live down 12 miles of graded gravel roads. So yes, I need tires that can take it. Drive fast ? Yes I sometimes pull at 65 mph. That would be "redline" on many ST tires. I don't run my engine at redline, why would I want to run my tires at redline ?
    Extremes ? Try I-40 through Oklahoma City !;):(


    I found this discussion because of my interest in replacing my ST tires on my 5th wheel. My new interest in this subject was due to having a blow out on I75 yesterday in Florida as we were making our way home. There is nothing quite so stimulating as attempting to change a tire on the drivers side of a 5th wheel while being nearly blown over by every passing truck of which there were many.

    I had about 20 hrs of driving time in the past two days to debate the need to replace all of our 5er tires which all appeared in good shape with proper inflation. I was only traveling about 60 mph at the time, but who knows what the internal condition of the tire was. I know the point was made regarding the difference in cost of ST vs LT and the frequency of change. I think we need to add the 3rd variable of cost of repair due to blow out damage. Our damage appears relatively light, aluminum skirt behind tire bent severely upwards, plastic trim piece broken off along with mounting bracket, and some underside damage as we now have road debris on the floor inside the 5er. Probably $1000-2000. I was initially thinking new STs but now LTs are starting to look like a better solution, no speed limit issues, load rating is OK. Not sure I even want to keep the STs for a spare after this occurance and it's the 2nd time in 3yrs.
    Glad you are OK.
    As you have found, the damages can be severe...
    But I think that there is a fourth cost as well.

    Time. My time off is precious to me. I don't want to spend it on a problem. A blowout can ruin and end a trip. That is something that I can never get back.
  • rbpru's avatar
    rbpru
    Explorer II
    Mar 31, 2016
    Well we have had six pages of information, opinions and rhetoric. By now a person should be able to decide if they want LTs or STs.

    One thing is for sure, the trailer industries; horse, boat, utility and RV are not about to change from STs any time soon. Maybe someday when cars and TTs are computer driven at crusing speed around 150 mph or levitated on magnetic rail highways at 200 mph; tire requirements will change.

    Till then, the millions of TT and 5ver on the road will continue to roll along on STs.

    Safe travels to all.
  • 4bearhug's avatar
    4bearhug
    Explorer
    Mar 31, 2016
    gmw photos wrote:
    rbpru wrote:
    If you folks are trying to say that LTs are tested to tougher standards than and ST there is no argument there. LTs are a more rubust tire because they need to be for their intended service.

    If you are trying to say the more robust testing makes them better for TT service, that is simply opinion.

    Those opinion is off set by 1.) The fact that TT and most of the other trailer industries find STs a sutable and economic tire choice. 2.) The fact that LTs are not widely used or advertized by their manufacturers for trailer service.

    People can invent a thousand reason why this is true, again just more opinions.

    My opinion is STs are used because they do what they are designed and tested to do.

    It is also my opinion that those who, go off-road, drive fast, exposed their rigs to other extremes or simply feel they need them; would best be served by a tire designed for that purpose.


    If I have to replace a $80 ST tire at 3 to 5 years, vs only having to replace a LT tire at twice that lifespan at $110, which is "more economic" ?

    Let's see, you mentioned off road. Yep, sometimes down rock roads to remote CG's. When I go to the farm to see my niece and her family, they live down 12 miles of graded gravel roads. So yes, I need tires that can take it. Drive fast ? Yes I sometimes pull at 65 mph. That would be "redline" on many ST tires. I don't run my engine at redline, why would I want to run my tires at redline ?
    Extremes ? Try I-40 through Oklahoma City !;):(


    I found this discussion because of my interest in replacing my ST tires on my 5th wheel. My new interest in this subject was due to having a blow out on I75 yesterday in Florida as we were making our way home. There is nothing quite so stimulating as attempting to change a tire on the drivers side of a 5th wheel while being nearly blown over by every passing truck of which there were many.

    I had about 20 hrs of driving time in the past two days to debate the need to replace all of our 5er tires which all appeared in good shape with proper inflation. I was only traveling about 60 mph at the time, but who knows what the internal condition of the tire was. I know the point was made regarding the difference in cost of ST vs LT and the frequency of change. I think we need to add the 3rd variable of cost of repair due to blow out damage. Our damage appears relatively light, aluminum skirt behind tire bent severely upwards, plastic trim piece broken off along with mounting bracket, and some underside damage as we now have road debris on the floor inside the 5er. Probably $1000-2000. I was initially thinking new STs but now LTs are starting to look like a better solution, no speed limit issues, load rating is OK. Not sure I even want to keep the STs for a spare after this occurance and it's the 2nd time in 3yrs.
  • gmw_photos's avatar
    gmw_photos
    Explorer
    Mar 29, 2016
    rbpru wrote:
    If you folks are trying to say that LTs are tested to tougher standards than and ST there is no argument there. LTs are a more rubust tire because they need to be for their intended service.

    If you are trying to say the more robust testing makes them better for TT service, that is simply opinion.

    Those opinion is off set by 1.) The fact that TT and most of the other trailer industries find STs a sutable and economic tire choice. 2.) The fact that LTs are not widely used or advertized by their manufacturers for trailer service.

    People can invent a thousand reason why this is true, again just more opinions.

    My opinion is STs are used because they do what they are designed and tested to do.

    It is also my opinion that those who, go off-road, drive fast, exposed their rigs to other extremes or simply feel they need them; would best be served by a tire designed for that purpose.


    If I have to replace a $80 ST tire at 3 to 5 years, vs only having to replace a LT tire at twice that lifespan at $110, which is "more economic" ?

    Let's see, you mentioned off road. Yep, sometimes down rock roads to remote CG's. When I go to the farm to see my niece and her family, they live down 12 miles of graded gravel roads. So yes, I need tires that can take it. Drive fast ? Yes I sometimes pull at 65 mph. That would be "redline" on many ST tires. I don't run my engine at redline, why would I want to run my tires at redline ?
    Extremes ? Try I-40 through Oklahoma City !;):(
  • Atlee's avatar
    Atlee
    Explorer II
    Mar 29, 2016
    I would like a 75 mph ST tire, rather than a 65 mph tire, but only because it's designed to handle the additional heat generated by the higher speed.

    That said, even if my ST tires were speed rated for 75 mph, I would still pull my trailer at under 65 mph. I see no need pulling my rig at 75 mph.
  • rbpru's avatar
    rbpru
    Explorer II
    Mar 29, 2016
    If you folks are trying to say that LTs are tested to tougher standards than and ST there is no argument there. LTs are a more rubust tire because they need to be for their intended service.

    If you are trying to say the more robust testing makes them better for TT service, that is simply opinion.

    Those opinion is off set by 1.) The fact that TT and most of the other trailer industries find STs a sutable and economic tire choice. 2.) The fact that LTs are not widely used or advertized by their manufacturers for trailer service.

    People can invent a thousand reason why this is true, again just more opinions.

    My opinion is STs are used because they do what they are designed and tested to do.

    It is also my opinion that those who, go off-road, drive fast, exposed their rigs to other extremes or simply feel they need them; would best be served by a tire designed for that purpose.
  • gmw_photos's avatar
    gmw_photos
    Explorer
    Mar 28, 2016
    rbpru wrote:
    ....much snippage....

    Tire choice for TT or TV is very subjective.


    If you would like to make it as simple as saying it's subjective, then fine, for sure since it's your trailer and your money, make it as "subjective" as you like.

    I and some others try to make decisions based more upon "objective" measures. The testing protocols that Huntindog showed us above would fall into the world of objective, rather than subjective.

    If you like to run ST tires, then so be it. There are suppliers to meet that need. If you like ST tires that are rated for 65 mph, that's fine too. Again there are suppliers to meet that need.

    But again, I go back to my earlier comment, I started this thread with a picture and description of a specific ST tire that meet an "objective" criteria, that being it is rated for 75 mph. My hope was to inform some folks that may find this tire useful is in fact being marketed.

    And for whatever little it may be worth, I have also stated in this thread ( and others ) that I have found the solution to trailer tires that meets my criteria. Lowest possible cost out the door on the date of sale is not at the top of my list. So I choose accordingly, and that has led me to LT.

    By the way....just returned home from a six state road trip, and the winter in Arizona. It was great to be out and about, but it's always nice to return home.
  • Huntindog's avatar
    Huntindog
    Explorer
    Mar 28, 2016
    RinconVTR wrote:
    Huntindog wrote:
    Boon Docker wrote:
    They know LT tires are not manufactured for trailer usage. This is why they do not advertise them as such.
    True, as far as that statemnt goes. BUT, LT tires are made for light trucks. They have to pass every test that an ST tire has to, and more tests that ST tires do not have to. This is not an opinion, this is a fact.

    In short, LTs are made to a higher standard.


    Prove it.

    LT's that are molded in sizes that fit our trailers are mostly LT's for trailer service only. They don't make them in sizes for trucks today. (There is a 16" size you can find some very old trucks running, but that's about it.)

    If the tire is marketed as trailer tire...ST or LT...prove to us they are tested differently.

    I can tell you the answer right now to save you time;

    You dont know what any given manufacture tests to. That is propitiatory information you wont find on the internet. So lets stop throwing out arbitrary information, eh?


    First off, 16" tires are widely available, and not for old vehicles.
    You are thinking of the old 16.5s.

    Secondly, here is your proof. And it didn't take long at all.

    The following is old post from a member that took the time to read all of the Govt. tire testing standards. It is a very difficult read as it keeps refering you to different subsections for details. Senior GNC did a lot of work on this and put together this summary complete with links to all of the info needed to verify it. I and others have checked this info out in the past and it is accurate. Unfortuantly, the govt. website has been redone and the links no longer work. The info is still available for one who is willing to wade thru the govt. website.

    Here it is:    This post is an open letter to the RV.net community whom have been following the ongoing tire discussions.

    I have been following these discussions, but until lately I have been staying on the sidelines until the topic took a turn to a more factual basis. I have personally experienced multiple failures with my 5th wheel and ST tires, both D and E load range and would like to understand why this appears to happen more often with ST (special trailer) vs. LT (light truck) tires. (Based on this forum it must be considered anecdotal and not conclusive evidence.)

    To resolve this matter I have investigated the current Federal Motor Carrier Safety Administration (FMCSA) testing standards that ST and LT tires must meet to be certified to be sold in the United States.

    First I have some folks that I would like to thank for providing me the desire to delve into this issue:
    “Chris” for moving the topic in a more factual direction.
    “Tireman9” for helping me find the federal standards.
    “FastEagle” for his willingness to challenge group thought and to encourage me to understand the perceived performance discrepancies between these types of tires.
    Thanks guys!

    For those of you who just wish to get the big picture facts, I have started with a summary section. This hits all the high points and you my quit after reading this. (No need to read all the details if you don’t want to!)

    If you wish to understand my research in greater depth (and verify my findings and conclusions), after the summary I have provided the following sections: references, notes, and testing of (1) bead unseating resistance, (2) strength, (3) endurance, and (4) high speed performance.

    SUMMARY OF FINDINGS & CONCLUSIONS

    I found the testing requirements for both the ST and LT tires at the Federal Motor Carrier Safety Administration (FMCSA) webpage.

    The testing for each tire is comprised of (1) bead unseating resistance, (2) strength, (3) endurance, and (4) high speed performance.

    The testing for (1) bead unseating resistance and (2) strength were identical for tires representative of moderate to heavy 5th wheels and thus no advantage is given to either tire type.

    The testing for (3) endurance was found to be significantly different between the ST and LT tires.

    Both the ST and LT are put through the same initial pressure, time and load profile. The total profile lasts 34 hours of continuous run time starting at 85% of rated load and ending at 100% of rated load. To further stress the tires, a load range E tire (nominal 80 psi rating) is tested at a reduced pressure of 60 psi to induce additional load on the tire during testing. (This is reasonable that testing should be conservative.)

    But now the endurance testing diverges significantly.

    The ST tire is tested at this pressure, time and load profile at 50 mph. After that, the ST test is over.

    The LT tire is tested at this pressure, time and load profile at 75 mph. This is a 50% increase over the ST and will induce significant additional load and heating on the tire during testing. After that, the LT test is not complete. Next a “Low Inflation Pressure Performance” test is performed for the LT tire only. The tire pressure is decreased to 46 psi and the tire is immediately run for an additional 2 hours at 75 mph and 100% of rated load.

    Thus, the LT tire endurance test is drastically more intense than the ST endurance test.

    The testing for (4) high speed performance.

    The difference in high speed performance testing between a ST and LT tire is significant. Both tires are tested through a 90 minute speed/time profile.

    The ST tire is tested 88% of rated load while the LT tire is tested at 85% of rated load. Thus, the loading is 3% higher based on rated load and this slight advantage goes to the ST tire.

    However, the LT tire is tested at significantly higher velocities when compared to a ST tire (99 vs. 85 mph maximum speed). This is a 16% advantage to the LT tire.

    Thus, again the overall test for the LT is more rigorous than the ST test.

    Conclusion:

    It is reasonable to conclude that these test requirements force the tire manufacturer to construct an LT tire more substantially than an ST tire. This is also a reasonable explanation for the same size LT tire is rated at a slightly lower maximum load than a ST tire.

    And now, for those of you who need to know all the details, read on!

    REFERENCES

    The references for my evaluation may be found at the Federal Motor Carrier Safety Administration (FMCSA) webpage:
    ST tire standard may be found at FMCSA Part 571, subsection 109.
    http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?chunkKey=090163348008f295
    LT tire standard may be found at FMCSA Part 571, subsection 139.
    http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?chunkkey=090163348008f2a9
    Part 571, subsection 139 references Part 571 subsection 119 which can be found at:
    http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?chunkKey=090163348008f29d

    QUICK NOTES

    Each standard for the ST and LT tires has definitions, significant constraints on labeling, etc. that I will not address. There are also tire conditioning (temperature), tire break in, etc. that are the same or similar for ST and LT that I will not address. The details are in the references.

    The (3) endurance, and (4) high speed performance tests must not result in tire failure. Tire failure includes visual evidence of tread, sidewall, ply, cord, inner liner, or bead separation, chunking, broken cords, cracking, or open splices, not just a blowout.

    TESTING - BEAD UNSEATING RESISTANCE

    ST Tire: (reference paragraph S5.2.2)

    The tire is mounted horizontally and a vertical load is applied to the tire’s outer sidewall at a rate of 50 mm (2 inches) per minute.

    Increase the load until the bead unseats or a specified value is reached.

    Repeat the test at least four places equally spaced around the tire circumference.

    LT Tire:

    Paragraph “S6.6 Tubeless tire bead unseating resistance” references the ST tire procedure noted above.

    Conclusion:

    The testing for bead unseating resistance is identical for a ST and LT tire.

    TESTING - STRENGTH

    ST Tire: (reference paragraph S5.3.2.1)

    Force a 19 mm (3?4 inch) diameter cylindrical steel plunger with a hemispherical end perpendicularly into the tread rib as near to the centerline as possible, avoiding penetration into the tread groove, at the rate of 50 mm (2 inches) per minute.

    Compute the breaking energy for each test point by means of a provided formula.

    LT Tire: (reference paragraph S6.5.2)

    Each tire shall comply with the requirements of S7.3 of 571.119, which is tires for vehicles weighing 10,000 lb or more. Per S7.3 of 571.119 for our example tire, the testing is the same as the ST tire procedure noted above.

    Conclusion:

    The testing for strength is identical for a ST and LT tire.

    TESTING - ENDURANCE

    The following is for a ST or LT tire of less than nominal cross section less than or equal to 295 mm (11.5 inches) which is typical of a 5th wheel application.

    ST tire: (reference paragraph S5.4.2)

    There are specifications for the contact of the tire mounted on a test axle and steel test wheel after the test that I will not address because they are similar for the ST and LT.

    Inflate a load range E to 60 psi. (410 kPa)

    Conduct the test at 80 kilometers per hour (km/h)(50 miles per hour) in accordance with the following schedule without pressure adjustment or other interruptions:

    The loads for the following periods are the specified percentage of the maximum load rating marked on the tire sidewall:
    Time and Percent of rated load
    4 hours, 85%
    6 hours, 90%
    24 hours, 100%

    LT Tire: (reference paragraph S6.3.1.2)

    “Conduct the test, without interruptions, at the test speed of not less than 120 km/h…” (75 mph)

    Inflate a load range E to 60 psi. (410 kPa)

    This test uses the same profile as the ST tire.

    Immediately following the above sequence perform a Low Inflation Pressure Performance test (reference paragraph S6.4):
    This test uses the same tire/wheel as the previous sequence at a reduced pressure.

    For a load range E tire the pressure is reduced to 46 psi. (320 kPa)

    The same tire/wheel is run an additional 2 hours at the reduced pressure at a speed of 75 mph and 100% of rated load.

    Conclusion:

    The difference in endurance testing between a ST and LT tire is significant. Both tires are tested through a equivalent loading/time profile. However, the LT tire is tested at this profile at a higher speed (75 vs. 50 mph) and must still endure an additional 2 hour low pressure test without failure. Thus the overall test for the LT is far more rigorous than the ST test.

    TESTING - HIGH SPEED PERFORMANCE

    ST tire: (reference paragraph S5.5.4)

    Load the tire to 88 percent of the tire’s maximum load rating as marked on the tire sidewall. Inflate to 72 psi (500 kPa). Run the test sequentially without interruption at:
    75 mph (121 km/h) for 30 minutes
    80 mph (129 km/h) for 30 minutes
    85 mph (137 km/h) for 30 minutes

    LT Tire: (reference paragraph S6.2.1.2.7)

    Load the tire to 85 percent of the tire’s maximum load rating as marked on the tire sidewall. Inflate to 72 psi (500 kPa). Run the test sequentially without interruption at:
    87 mph (140 km/h) for 30 minutes
    93 mph (150 km/h) for 30 minutes
    99 mph (160 km/h) for 30 minutes

    Conclusion:

    The difference in high speed performance testing between a ST and LT tire is significant. Both tires are tested through a speed/time profile. The ST tire is tested 88% of rated load while the LT tire is tested at 85% of rated load. Thus, the loading is 3% higher based on rated load and this slight advantage goes to the ST tire. However, the LT tire is tested at significantly higher velocities (nearly 100 mph!) when compared to a ST tire. This is a 16% advantage to the LT tire. Thus, again the overall test for the LT is more rigorous than the ST test.

    * This post was edited 09/23/09 04:30pm by SeniorGNC *


    Link to the OP:

    ST vs. LT tire testing standards

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