Replace ST tire with LT tire

[Tireman9]

Originally Posted by Titanguy

I have been in the tire business all my life and the term reserve capacity is used to describe the difference in the GVWR and the combined load capacity of the tires.

Example: a 2015 Ford Escape has a GVWR of 4,720 lbs.
Tire is a 235/50R18 97S Load Capacity 1608 lbs.
So at the GVWR of 4,720 lbs. this vehicle is 73% loaded or has a 27% reserve capacity.

Reserve capacity is NOT some unknown number.

x2

Numbers for most cars made today are similar with a 12% Reserve Capacity being the lowest I recall seeing.

Gee do you think Ford and the other car companies that have actual engineers responsible for tire selection know something the RV companies don't? Does anyone think that a reserve capacity of 1.4% is a good idea?

[Secbyte]

I really do not get people who feel running LT tires on a trailer is ok. The sidewall strength is just not there and a Light Truck does not have the sidewall flex that a tandem wheel does. Notice when you have a truck that has tandem wheels it is no longer a Light Truck but a commercial truck with yet again different tires. ST stands for Special Trailer and it is designed to carry not only the weight of your rig, but that weight is constant, not like a truck that spends 50% of its time empty, but does not experience the same engineering forces a truck does.


For example watch a trailer tire around a sharp turn going slowly so you can see it. The fight that trailer tire has between gripping the road like it should, fighting the tread, and flexing the sidewall to do so is even a bit scary to look at. a Special Trailer tire is designed to do just that.


Now a China tire VS a American tire or a substandard American tire is another discussion altogether. If you buy a quality American tire you should not have blowout issues.

[tuffr2]

You are missing the point!! Airstream is already putting LT tires on their trailers as standard equipment. And did you read any of the posts with tire weight? LT tires weigh more. Must be the air that weighs more huh?

[Tireman9]

Originally Posted by Secbyte

I really do not get people who feel running LT tires on a trailer is ok. The sidewall strength is just not there and a Light Truck does not have the sidewall flex that a tandem wheel does. Notice when you have a truck that has tandem wheels it is no longer a Light Truck but a commercial truck with yet again different tires. ST stands for Special Trailer and it is designed to carry not only the weight of your rig, but that weight is constant, not like a truck that spends 50% of its time empty, but does not experience the same engineering forces a truck does.

For example watch a trailer tire around a sharp turn going slowly so you can see it. The fight that trailer tire has between gripping the road like it should, fighting the tread, and flexing the sidewall to do so is even a bit scary to look at. a Special Trailer tire is designed to do just that.

Now a China tire VS a American tire or a substandard American tire is another discussion altogether. If you buy a quality American tire you should not have blowout issues.

Please don't confuse "tandem" two tires one in front of the other on different axles with "Dual" two tires side by side on the same axle.

Tires in Dual application have a load capacity reduction as shown in the Load/Inflation tables. IMO I think that tires in tandem application should have the same reduction.

RE load capacity. It is the air pressure that supports the load not the sidewall. The sidewall "strength" is designed to hold the pressure. Sidewall bending strength i.e. stiffness is not just a function of rubber thickness but of the body cord placement and reinforcement angle. Simply adding more sidewall rubber will certainly increase the thickness but do almost nothing extra to retain the pressure.

ST tires have higher load capacity for an equal size and inflation than LT for a few reasons such as reduced tread thickness, lower max speed capability are the two major reasons. ST tires also do not have to pass the more challenging safety standards required of LT type tires.

I have not seen data that supports the idea that an LT tire will not perform satisfactorily in trailer application when the load capacity and inflation are properly calculated with an appropriate safety margin. I am aware of many claims of ST tires failing even when the RV company is suppose to consider tire usage including loads when the company selects the tires and identifies the inflation on the placard.

Sidewall "Blowouts" or more properly sidewall flex failures are the result of running a tire when significantly under-inflated, usually due to puncture, cut or valve leak.

[Cumminsfan]

LT tires are standard on a high end 5th wheels. I guess you have to pay more to get the wrong tires. Geez. Any MFG besides the high enders would use them but they cost too much. RV's need to be competitive and every penny counts. That's why until you get near $100,000 you get the same level of equipment but more bling. Spend the big $$$$ and you get the bling as well as the better equipment.
It's not an ST vs LT tire rating thing. It's a $$$ thing.
How many times do we read about some guy with Ching Chang ST tires having a blowout months after purchase? I've never read anywhere on any RV forum about someone putting LT tires on their trailer and having a blowout soon after.

[Cumminsfan]

FWIW besides DVR, Redwood, Lifestyle, etc, Heartland Big Horn, Big Country and Landmark365 all have LT tires, as standard equipment. I'm sure there are other more expensive trailer MFG's who also install LT tires on their trailers.
Too all you anti LT tire guys, why would those MFG's put an LT tire on their trailers if LT tires are inferior and not suitable?

[FastEagle]

Originally Posted by Cumminsfan

FWIW besides DVR, Redwood, Lifestyle, etc, Heartland Big Horn, Big Country and Landmark365 all have LT tires, as standard equipment. I'm sure there are other more expensive trailer MFG's who also install LT tires on their trailers.
Too all you anti LT tire guys, why would those MFG's put an LT tire on their trailers if LT tires are inferior and not suitable?

You're up into the 7000# axles. The LTs had a foothold on that market before the ST235/85R16 load range F&G came along. And, the first LTs to be regulars in that market were steel cased tires designed for trailer service only. Now there are a lot of off shore manufacturers building the same tires for a lot less. The popular Sailun is one of them.

Once you get into the 17.5" tires found on many of the 7000# & 8000# axles you are into the medium duty low platform truck/trailer tires.

[Secbyte]

I am not confusing anything. I work admittedly not as a tire engineer, but as a tire dealer. We do not put LT tires on trailers.


But to refute the blasting points above in my honest opinion....


If I had to guess about why Airstream does anything, I would guess that Airstreams are far lighter than most trailers. But as a businessman, if Airstream or any other manufacturer wants to put LT tires on their vehicles it is because they are cheaper. Not because there is some ST tire conspiracy going on. Sell 10 thousands units save $400.00 per unit on LT tires, that is 4 million in extra profit. As long as they reach the end of the warranty that is not their problem, and can blame it all on UV or roadhazzard when they go.


All I am saying here is there is a product designed and sold to do what I want and the tire manufacturer recommends it, why would I roll the dice to save $400, when it could cost me my rig. Do what you want I did not come here to fight with you guys especially when you take to saying things like those below. If you want to argue please argue with someone else, I said I just did not get it, not please answer me with some idiotic statement like I guess Air weighs more Huh?


No I don't think the air weighs more, and by the way, that is a childish response, But I do think ST tires they have less tread, and less aggressive tread on them. less tread and less aggressive tread means less weight. But I don't think its because air weighs more.


As much as I agree that sidewall failures are because of underinflated, I have watched my properly inflated tires on pavement on my trailers flex. I am not positive here and at the risk of getting beat up by more of you, I think flex of any kind is not good for the sidewall, weather it is because of underinflating or flex from lateral forces.

[IC2]

Originally Posted by Secbyte

I am not confusing anything. I work admittedly not as a tire engineer, but as a tire dealer. We do not put LT tires on trailers.


But to refute the blasting points above in my honest opinion....


If I had to guess about why Airstream does anything, I would guess that Airstreams are far lighter than most trailers. But as a businessman, if Airstream or any other manufacturer wants to put LT tires on their vehicles it is because they are cheaper. Not because there is some ST tire conspiracy going on. Sell 10 thousands units save $400.00 per unit on LT tires, that is 4 million in extra profit. As long as they reach the end of the warranty that is not their problem, and can blame it all on UV or roadhazzard when they go.


All I am saying here is there is a product designed and sold to do what I want and the tire manufacturer recommends it, why would I roll the dice to save $400, when it could cost me my rig. Do what you want I did not come here to fight with you guys especially when you take to saying things like those below. If you want to argue please argue with someone else, I said I just did not get it, not please answer me with some idiotic statement like I guess Air weighs more Huh?


No I don't think the air weighs more, and by the way, that is a childish response, But I do think ST tires they have less tread, and less aggressive tread on them. less tread and less aggressive tread means less weight. But I don't think its because air weighs more.


As much as I agree that sidewall failures are because of underinflated, I have watched my properly inflated tires on pavement on my trailers flex. I am not positive here and at the risk of getting beat up by more of you, I think flex of any kind is not good for the sidewall, weather it is because of underinflating or flex from lateral forces.

Wow - what a bunch of erroneous information. I don't know you or your PA tire store, but have to say that I would never buy from you. This is from my Post #31 here

"When we were trailer hunting I asked a dealer how much extra good tires would cost. He ran the numbers, did our price negotiations with this as a non-negotiable adder. They were a $1500 and change adder.

Today, a China Bomb in the normal 235-85x16" size is $94 each at 35 pounds . A Michelin XPS Rib is $238 each at 56 pounds each plus shipping and installation **. A Goodyear G614 is in the $350 price range plus shipping and installation each. You can bet that an RV manufacturer is trying to maximize his profit as I can assure you that he buys the Bombs cheaper by the container load then $94/each.

(I really like my General Grabber LRR's at $190 each including shipping and installation plus my TPMS tells me how well they are doing temp and pressurewise) "

Cheaper? Not hardly!!!!!!!!!!

**Tire Rack pricing the day I posted that tidbit

The benefits of an LT - others here have offered a great deal of great information that you should probably actually read instead of blasting in here new with some uninformed and absolutely incorrect statements.

Weight of an Airstream - you should also do your homework - a 31' Classic is ~7400 pounds dry with a GVWR of 10,000. A 'common' 31' Keystone Laredo - 6000 pounds and a GVWR of 8200 pounds, other brands, similar.

[Cumminsfan]

99% of the time LT tires cost more that ST. Go to Tirerack and look up prices. The Michelins that Airstream run are in the $200+ range. No ST tire in a 235/75/16 cost that much.
My Northwood trailer comes with GY Marathon ST tires. One of the better ST brands out there. Northwood has a reputation for building solid heavy trailers that cost a little more than the competition. It would be a big disappointment if they put some Ching Chang ST tire on.


Airstream could put cheap blowout prone ST tires on their trailers, but that goes against the overall concept of an Airstream. Why load up your trailer with higher quality amenities and then put cheap tires on.
It would be like buying a Mercedes expecting leather and you get vinyl seats.

[FastEagle]

Originally Posted by Cumminsfan

99% of the time LT tires cost more that ST. Go to Tirerack and look up prices. The Michelins that Airstream run are in the $200+ range. No ST tire in a 235/75/16 cost that much.
My Northwood trailer comes with GY Marathon ST tires. One of the better ST brands out there. Northwood has a reputation for building solid heavy trailers that cost a little more than the competition. It would be a big disappointment if they put some Ching Chang ST tire on.


Airstream could put cheap blowout prone ST tires on their trailers, but that goes against the overall concept of an Airstream. Why load up your trailer with higher quality amenities and then put cheap tires on.
It would be like buying a Mercedes expecting leather and you get vinyl seats.

You should read around in other forums. In the Heartland forum it’s the Towmax bombs. In the Airstream forum it’s the Marathon bombs. In the NuWa forum it used to be the G614 bombs, now they are using off shore tires. And some time ago in the Keystone forums it was all about the Lerado & Mission tires. Feedback about causes are not an after thought. Just the fact that the tires suffered catastrophic failures.

[tuffr2]

Cumminsfan mentioned the tire that Airstream uses on their was a Michelin LTX M/S tire. That is correct but but I want to mention unlike the Michelin XPS Ribs the LTX M/S tire is a more 'normal' tire that also is standard eqipment on the Honda Ridgeline.

Also it was mentioned that Airstream trailers are heavy...X2 on that comment.

[Tireman9]

Ok everyone I'll toss the grenade over the wall.

In DOT Federal Regulations there is a section
"§571.110 Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less."

It says "S1. Purpose and scope. This standard specifies requirements for tire selection to prevent tire overloading and for motor home/recreation vehicle trailer load carrying capacity information."


The regulation has a number of definitions of terms and includes this for LT tires "Light truck (LT) tire means a tire designated by its manufacturer as primarily intended for use on lightweight trucks or multipurpose passenger vehicles."


Passenger car tires are also defined but interestingly ST type tires are not defined in this section.


Section S.4 are the requirements
"S4.1 General. Vehicles shall be equipped with tires that meet the requirements of §571.139, New pneumatic tires for light vehicles, except that passenger cars may be equipped with a pneumatic T-type temporary spare tire assembly that meets the requirements of §571.109, or equipped with a non-pneumatic spare tire assembly that meets the requirements of §571.129, New non-pneumatic tires for passenger cars, and S6 and S8 of this standard. Passenger cars equipped with a non-pneumatic spare tire assembly shall meet the requirements of S4.3(e), and S5, and S7 of this standard."


NOTE ST type tires are specifically NOT covered by 571.139.


These sections of 571.110 cover the use of P type tires and the load capacity de-rating
"S4.2.2.1 Except as provided in S4.2.2.2, the sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.
S4.2.2.2 When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle."


=====
I find no mention of the use of ST type tires in the selection of tires for Recreation Vehicles.


I may have made an error


Can anyone more familiar with 49 CFR 571 than I am please help me find my error and identify the section that specifies the requirement to use ST type tires in RV use?

[FastEagle]

Originally Posted by Tireman9

Ok everyone I'll toss the grenade over the wall.

In DOT Federal Regulations there is a section
"§571.110 Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less."

It says "S1. Purpose and scope. This standard specifies requirements for tire selection to prevent tire overloading and for motor home/recreation vehicle trailer load carrying capacity information."


The regulation has a number of definitions of terms and includes this for LT tires "Light truck (LT) tire means a tire designated by its manufacturer as primarily intended for use on lightweight trucks or multipurpose passenger vehicles."


Passenger car tires are also defined but interestingly ST type tires are not defined in this section.


Section S.4 are the requirements
"S4.1 General. Vehicles shall be equipped with tires that meet the requirements of §571.139, New pneumatic tires for light vehicles, except that passenger cars may be equipped with a pneumatic T-type temporary spare tire assembly that meets the requirements of §571.109, or equipped with a non-pneumatic spare tire assembly that meets the requirements of §571.129, New non-pneumatic tires for passenger cars, and S6 and S8 of this standard. Passenger cars equipped with a non-pneumatic spare tire assembly shall meet the requirements of S4.3(e), and S5, and S7 of this standard."


NOTE ST type tires are specifically NOT covered by 571.139.


These sections of 571.110 cover the use of P type tires and the load capacity de-rating
"S4.2.2.1 Except as provided in S4.2.2.2, the sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.
S4.2.2.2 When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle."


=====
I find no mention of the use of ST type tires in the selection of tires for Recreation Vehicles.


I may have made an error


Can anyone more familiar with 49 CFR 571 than I am please help me find my error and identify the section that specifies the requirement to use ST type tires in RV use?

It's not there. They write in generalities. However, in 571.119 under S3 in applications the ST tire is mentioned so when qualifying tires are not mentioned specifically, that application statement would apply.

In most cases the FMVSS need to be married with tire industry standards to come to a conclusion on many fitment issues.

CFR 570.9 & 570.62 are both active regulations. And although not mentioned very often they have a significant impact on replacement tire selections and tire industry standards because they set the precedent for formal tire inspections by any authority.