LT vs ST tires good read

[CaptnJohn]

Trailer King load range E are rated for 75 mph...

[emm-dee]

The linked article was very interesting and informative. However, claims that ST tires are more robust than LT tires are comparing apples to oranges. Sure, an ST may be stronger than an identically sized LT but you'll have a hard time finding a 15 inch LT.

The claims that one has to have ST because LT does not require as much side load capacity seem suspicious. A trailer tire should experience minimally more side load than a truck tire experiences, but it does not experience the loads caused by acceleration. What difference does it make if one has a, i.e., ST225/75R15 rated at 2,500 pounds or a LT225/70R16 also rated at 2,500 pounds mounted on the trailer. Both of those tires have an 8.9 inch tread width but the 16 incher is 1/10 of an inch taller...insignificant. The important thing is that either tire used must have an adequate (actually, much more than adequate) weight limit.

I'm not sure of the reasoning behind Goodyears statement about wider not being better for a trailer tire, but I'll defer to their expertise and accept that.

Now...consider hydroplaning. Here's where the LT tire shines. Most LT tires (not all, but most) are inflated to 80 psi. Most ST tires (again, not all but most) are inflated to 65 psi. Based on ⅛ inch of standing water, the basic rule is that hydroplaning occurs at a speed which equals nine times the square root of the pressure. For an 80 psi tire that is 80 mph and for a 65 psi tire that is 72 mph. The Goodyear 614 at 110 psi has a basic hydroplaning speed of 94 mph. And, an E-rated 10 ply ST tire uses 80 psi so it becomes equal to the LT.

Don't take those numbers as an operating limit (or goal) because they can change a lot with ¼ inch of water, oil mixed with water, etc etc.

[Oaklevel]

Originally Posted by emm-dee

The linked article was very interesting and informative. However, claims that ST tires are more robust than LT tires are comparing apples to oranges. Sure, an ST may be stronger than an identically sized LT but you'll have a hard time finding a 15 inch LT.

The claims that one has to have ST because LT does not require as much side load capacity seem suspicious. A trailer tire should experience minimally more side load than a truck tire experiences, but it does not experience the loads caused by acceleration. What difference does it make if one has a, i.e., ST225/75R15 rated at 2,500 pounds or a LT225/70R16 also rated at 2,500 pounds mounted on the trailer. Both of those tires have an 8.9 inch tread width but the 16 incher is 1/10 of an inch taller...insignificant. The important thing is that either tire used must have an adequate (actually, much more than adequate) weight limit.

I'm not sure of the reasoning behind Goodyears statement about wider not being better for a trailer tire, but I'll defer to their expertise and accept that.

Now...consider hydroplaning. Here's where the LT tire shines. Most LT tires (not all, but most) are inflated to 80 psi. Most ST tires (again, not all but most) are inflated to 65 psi. Based on ⅛ inch of standing water, the basic rule is that hydroplaning occurs at a speed which equals nine times the square root of the pressure. For an 80 psi tire that is 80 mph and for a 65 psi tire that is 72 mph. The Goodyear 614 at 110 psi has a basic hydroplaning speed of 94 mph. And, an E-rated 10 ply ST tire uses 80 psi so it becomes equal to the LT.

Don't take those numbers as an operating limit (or goal) because they can change a lot with ¼ inch of water, oil mixed with water, etc etc.

Just askin why would it be hard to find an LT in a 15 inch that is / was the most common size of Light truck tires????????. and as I mentioned why does Goodyear recommend ST or trailer rated tires on trailers and most reputable tire dealers refuse to put Light Truck tires on trailers .

[emm-dee]

Originally Posted by Oaklevel

Just askin why would it be hard to find an LT in a 15 inch that is / was the most common size of Light truck tires????????. and as I mentioned why does Goodyear recommend ST or trailer rated tires on trailers and most reputable tire dealer refuse to put Light Truck tires on trailers .

I've checked the Michelin, BFG, Goodyear, Firestone/Bridgestone, etc, and other reputable (read non-chinese tire builders) and can only find LT in 16 inch or larger. The 15 inch 10-ply tires seem to only be available as ST tires.

[Oaklevel]

Originally Posted by emm-dee

I've checked the Michelin, BFG, Goodyear, Firestone/Bridgestone, etc, and other reputable (read non-chinese tire builders) and can only find LT in 16 inch or larger. The 15 inch 10-ply tires seem to only be available as ST tires.

I used 15" LT tires on all my F150s maybe I misunderstood you You didn't say you were talking about 10 ply tires. LT 15s Tires are made by most of the manufacturers Goodyear, BF Goodrich and the others .

[emm-dee]

Originally Posted by Oaklevel

I used 15" LT tires on all my F150s maybe I misunderstood you You didn't say you were talking about 10 ply tires. LT 15s Tires are made by most of the manufacturers Goodyear, BF Goodrich and the others .

I probably wasn't clear. I just associate an LT tire with being a 10 ply tire. I also wasn't aware that any pickup truck was equipped with anything less than a 16 inch tire.

[Oaklevel]

Originally Posted by emm-dee

I probably wasn't clear. I just associate an LT tire with being a 10 ply tire. I also wasn't aware that any pickup truck was equipped with anything less than a 16 inch tire.

All the F150s and others had 15 in tires up through the 90s and maybe early 2000s. Can't afford new trucks so have no idea when they went to 16s

Back in the 90s there were big issues with Ford Dodge and Chey 3/4 and 1 tons some ran 16s some ran 16 1/2s and there were big issues making sure the 16.5in tires did not get on the 16 in rims

[checkmate99]

Originally Posted by emm-dee

The linked article was very interesting and informative. However, claims that ST tires are more robust than LT tires are comparing apples to oranges. Sure, an ST may be stronger than an identically sized LT but you'll have a hard time finding a 15 inch LT.

The claims that one has to have ST because LT does not require as much side load capacity seem suspicious. A trailer tire should experience minimally more side load than a truck tire experiences, but it does not experience the loads caused by acceleration. What difference does it make if one has a, i.e., ST225/75R15 rated at 2,500 pounds or a LT225/70R16 also rated at 2,500 pounds mounted on the trailer. Both of those tires have an 8.9 inch tread width but the 16 incher is 1/10 of an inch taller...insignificant. The important thing is that either tire used must have an adequate (actually, much more than adequate) weight limit.

I'm not sure of the reasoning behind Goodyears statement about wider not being better for a trailer tire, but I'll defer to their expertise and accept that.

Now...consider hydroplaning. Here's where the LT tire shines. Most LT tires (not all, but most) are inflated to 80 psi. Most ST tires (again, not all but most) are inflated to 65 psi. Based on ⅛ inch of standing water, the basic rule is that hydroplaning occurs at a speed which equals nine times the square root of the pressure. For an 80 psi tire that is 80 mph and for a 65 psi tire that is 72 mph. The Goodyear 614 at 110 psi has a basic hydroplaning speed of 94 mph. And, an E-rated 10 ply ST tire uses 80 psi so it becomes equal to the LT.

Don't take those numbers as an operating limit (or goal) because they can change a lot with ¼ inch of water, oil mixed with water, etc etc.

Good info emm-dee, but if you are traveling at 70mph towing your trailer when there is any chance of hydroplaning, you had better slow down!

[emm-dee]

Originally Posted by checkmate99

Good info emm-dee, but if you are traveling at 70mph towing your trailer when there is any chance of hydroplaning, you had better slow down!

Oh yes, I completely agree. Although I'm new to the travel trailer thing, I have decades of experience towing pretty heavy horse trailers which taught me that anything faster than 60-65 is just not worth the stress that comes with that. (I guess since most of my horse trailer had full living quarters they qualify as an RV).

[ependydad]

Originally Posted by donniedu

Do they really?
ST tires are load and speed rated to only 65 MPH
LT tires generally are speed and load rated at 99 MPH.
Which is better?

I'm not arguing "better" - I'm stating that the tires should be used within their stated specs. Look at the specs and you'll find that LT tires in equivalent sizes to ST tires have less stated carrying capacity.

[bob caldwell]

New ST Carlisle's are speed rated for 85

Sent from my XT1080 using Tapatalk

[mnoland30]

Even the industry doesn't yet seem to know that the standard for ST tires is changing. I've replaced all of my trailer tires with 14 and 15 inch D rated Taskmaster tires with a speed rating of M, which is 81 mph. Why settle for less? Even etrailer, where I purchased the tires, didn't know the speed rating, but it is molded into the tire. If we refuse to buy tires rated for 65 mph, they'll quit making them eventually.

[Airdale]

Originally Posted by spock123

My G614 came on the trailer from the factory. I guess you would have to call Cedar Creek on this one. I guess they are just stupid for installing the G614 on this camper.


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Tire manufacturers build tires to a set of specifications appropriate for each tire and it's intended usage. Vehicle manufacturer's may find that a specific tire will also be appropriate for their fitment purposes and make adjustments to the tire manufacturer's specifications. When they do so, such as in your case (if your G614s are mounted on 6" wide rims and identified as such on the trailer's certification label), they will also certify it to be a safe fitment via the certification process. However, because they do such things does not open the door for consumers to do the same. Consumers do not have the power of certification on their side.

[Oaklevel]

I may prefer to have my tires rated at above 65 but you will not likely see me pulling a trailer over 65 mph................ Pulling the trailer above 65 is no big deal......stopping 20,000 plus pounds going over 65 mph can be a big deal when you need to it it quickly........... In my years of traveling I see it all to often a 100 plus car pile up on I77 they all couldn't stop in time ....... even saw (it happen) two vehicles hit head on on a two lane road the Ford Focus lost even his life, the tractor trailer saw minor damage. Even though he was in the right he will live with the image forever............

[MillerTime]

Originally Posted by Airdale

Tire manufacturers build tires to a set of specifications appropriate for each tire and it's intended usage. Vehicle manufacturer's may find that a specific tire will also be appropriate for their fitment purposes and make adjustments to the tire manufacturer's specifications. When they do so, such as in your case (if your G614s are mounted on 6" wide rims and identified as such on the trailer's certification label), they will also certify it to be a safe fitment via the certification process. However, because they do such things does not open the door for consumers to do the same. Consumers do not have the power of certification on their side.

This is rather questionable logic.
I can see no reason why an upgraded tire would be a problem. Who cares if it's the same as what the manufacturers originally spec, if it exceeds it?

Remember the Ford/firestone fiasco of about 12-15 years ago?? Have you read anything about the sandpiper/sierra campers that were sent out with axle/wheel/tire campers that were WAY too light and ended up being very problematic?

Manufacturers get it wrong sometimes and whatever tire "authority" you think you have is severely flawed in your stating that someone is wrong in upgrading to g614's from their original 10ply lesser brand tires.

[doc73]

If the tire makers use some "standard" making these things they sure suck at it!!

I know this brought bad blood last time this was posted, but Airdale, I though the change in standard was on a paper from years ago and never went anywhere. I remember this, I think, from when I was looking to upgrade to 15" rim a few months back.. Which I never did because winter came.

[Airdale]

Originally Posted by Oaklevel

I used 15" LT tires on all my F150s maybe I misunderstood you You didn't say you were talking about 10 ply tires. LT 15s Tires are made by most of the manufacturers Goodyear, BF Goodrich and the others .

There are a number of 15" LT tires but not as high as LRE. The LT235/75R15D is a little larger than the ST225/75R15D but is very close to the same max load capacity at 2335#.

[northstar1960]

Special Trailer (ST) Tire Speed Ratings

Unless assigned a specific Speed Rating, industry standards dictate tires with the ST designation are speed rated to 65 mph (104 km/h) under normal inflation and load conditions.
However, Goodyear Marathon and Power King Towmax STR tires featuring the ST size designation may be used at speeds between 66 and 75 mph (106 and 121 km/h) by increasing their cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.
Do not exceed the wheel's maximum rated pressure. If the maximum pressure for the wheel prohibits the increase of air pressure, then maximum speed must be restricted to 65 mph (104 km/h).
The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire.
Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.

[Oaklevel]

Originally Posted by Airdale

There are a number of 15" LT tires but not as high as LRE. The LT235/75R15D is a little larger than the ST225/75R15D but is very close to the same max load capacity at 2335#.

I was just going by the blanket statement that was made that you could not buy 15 in LT tires which is not true.

[Airdale]

Originally Posted by MillerTime

This is rather questionable logic.
I can see no reason why an upgraded tire would be a problem. Who cares if it's the same as what the manufacturers originally spec, if it exceeds it?

Remember the Ford/firestone fiasco of about 12-15 years ago?? Have you read anything about the sandpiper/sierra campers that were sent out with axle/wheel/tire campers that were WAY too light and ended up being very problematic?

Manufacturers get it wrong sometimes and whatever tire "authority" you think you have is severely flawed im your stating that someone is wrong in upgrading to g614's from their original 10ply lesser brand tires.

The subject above is about rim size, not tire fitment to the trailer.

There are no firm tire industry standards for "plus sizing" RV trailer tires. That's why it's so hard to get a LT tire manufacturer to authorize the use of their LT tires as replacements for original equipment ST tires. However, the G614 IS a trailer tire. But, will the trailer manufacturer authorize it as a replacement for a smaller tire is the question? Brands have nothing to do with size and load capacity.

If you want to see a runaround about tire usage read the "not covered" section of this warranty package. If you are honest with Michelin and ask them if it's ok to use any of their LT tires to replace your OE ST tires they are going to say, NO! Your trailer owner's manual is going to tell you in the tire safety section to use replacement tires like the ones that came on it. Michelin has that covered in the last bullet in the " not covered" heading.

What an owner does is their responsibility. What NHTSA and the tire industry say is within the safety ropes. Once you step outside the ropes you are at your own risk.

http://media.michelinman.com/content...omise_Plan.pdf