ST to LT tires?

[FastEagle]

Originally Posted by kdauto

My '06 5th wheel had the GY Marathon load range D on it. It has a 14 400 GVWR and 6000 lb axlesx2. If the LRD tires carry 3000 lbs each that means they are right AT the limit for a 6000 lb axle.

I replaced them with LRE GY Marathons about 4 years ago. I used to run 80 psi in them, now doing 72-73 psi, much better and within all specs.

Keystone RV trailers often came with tires that matched the vehicle certified GAWRs. The OEM Marathons took a beating in the market place because of it. Other manufacturer's did the same thing with their OEM tires and got the same failure results. Even on well balanced axles and wheel positions, loaded to or close to GAWR values, all OEM tires failed early. There is no load capacity reserve requirement above the GAWR load capacity for the fitment of RV trailer tires in the FMVSS (standards).

Trying to get a better ride for your trailer by lowering tire inflation pressures below an acceptable load capacity reserve -10-15% - is just asking for trouble.

[FastEagle]

Originally Posted by kdauto

What is this 110 lbs of axle weight you're talking about? Would the weight of the axle not already be included in GAWR?

There is no requirement for an owner to exceed the load capacity of their OEM tires with replacements. There is a RVIA recommendation binding only on the vehicle manufacturer to provide 10% in load capacity reserves above the vehicle certified GAWRs. However, tire industry standards require replacement tires to provide a load capacity equal to the load capacity the OE/OEM tires provide.

To follow the RVIA recommendation, 6000# axles would require a tire inflation pressure that produces 3300# of load capacity. The simple math is to take your trailer's GAWR value from the certification label and multiply by 1.1 and divide that sum by 2 for a single tire minimum load capacity.

[kdauto]

Originally Posted by FastEagle

There is no requirement for an owner to exceed the load capacity of their OEM tires with replacements. There is a RVIA recommendation binding only on the vehicle manufacturer to provide 10% in load capacity reserves above the vehicle certified GAWRs. However, tire industry standards require replacement tires to provide a load capacity equal to the load capacity the OE/OEM tires provide.

To follow the RVIA recommendation, 6000# axles would require a tire inflation pressure that produces 3300# of load capacity. The simple math is to take your trailer's GAWR value from the certification label and multiply by 1.1 and divide that sum by 2 for a single tire minimum load capacity.

I have not seen that recommendation anywhere. I have searched for it. Most reputable tire,axle and wheel manufacturers DO leave in a safety factor that is likely at least 10%, probably 15 to 20% or more. That 73 psi cold most often hits 80 psi when driving on hot pavement for an hour or more. That 80 psi hot is supporting the 3420 lbs or so per tire.

My RV has nowhere near the 3000 lb load per tire. I am most likely close to 2600 lbs per tire on average (no RV is 100% balanced on all 4 wheels). I am obtaining 3250 lbs or so max load cold so as I have stated numerous times now, I am not anywhere near the danger zone. I have NOT told people to lower pressures to below what they need for THEIR actual loads and weights. I DID say people should weigh their rigs and adjust accordingly.

What IS unsafe is many RV manufacturers build mammoth sized rigs and allow such little cargo capacity it is shameful. I've seen 38' rigs with under 2000 lbs of capacity,some at 1500 lbs or less. No one buys a rig like that and only puts 3 dishes and 4 changes of clothes plus 1/4 tank of fresh water.

I wish people would read responses better before answering with erroneous info. THIS confuses the original poster and helps no one.

Weigh your rigs, use quality tires, adjust pressures according to YOUR needs and check regularly.

[Tireman9]

Originally Posted by krsmitty

Are you saying he should be running at 80 PSI? Which is what I plan to start doing...based on what I have read so far.

Yes as long as the wheels are rated for 80 psi. Some wheels are marked. for others you would need to contact the wheel company. RV phone person probably has no idea of wheel rating they can point to.

[Tireman9]

Originally Posted by kdauto

I have not seen that recommendation anywhere. I have searched for it. Most reputable tire,axle and wheel manufacturers DO leave in a safety factor that is likely at least 10%, probably 15 to 20% or more. That 73 psi cold most often hits 80 psi when driving on hot pavement for an hour or more. That 80 psi hot is supporting the 3420 lbs or so per tire.

My RV has nowhere near the 3000 lb load per tire. I am most likely close to 2600 lbs per tire on average (no RV is 100% balanced on all 4 wheels). I am obtaining 3250 lbs or so max load cold so as I have stated numerous times now, I am not anywhere near the danger zone. I have NOT told people to lower pressures to below what they need for THEIR actual loads and weights. I DID say people should weigh their rigs and adjust accordingly.

What IS unsafe is many RV manufacturers build mammoth sized rigs and allow such little cargo capacity it is shameful. I've seen 38' rigs with under 2000 lbs of capacity,some at 1500 lbs or less. No one buys a rig like that and only puts 3 dishes and 4 changes of clothes plus 1/4 tank of fresh water.

I wish people would read responses better before answering with erroneous info. THIS confuses the original poster and helps no one.

Weigh your rigs, use quality tires, adjust pressures according to YOUR needs and check regularly.

HERE is the 10% margine info.


All discussions of inflation and load capacity are ,or should be, based on COLD inflation pressure. It is not proper to inflate and then depend on the tire warming up to achieve your desired inflation.

[IC2]

In 2009, I had a choice of GY Marathon's or Carlisle so went to an LT (General Grabber LRR). In 2014, another 5er and came with a 'famous' Chinese built POS so again - my choce was Marathons, another Chinese tire or an LT. Back to the Generals. After about 50K miles with these tires I am satisfied that they work the best for our needs. Next year will be the year for new tires. Maybe Sailuns, mor Generals or the Michelin XPS Ribs but never another ST Chinese low end tire.

[kdauto]

Originally Posted by Tireman9

HERE is the 10% margine info.

All discussions of inflation and load capacity are ,or should be, based on COLD inflation pressure. It is not proper to inflate and then depend on the tire warming up to achieve your desired inflation.

Thanks for that info/link. Although having the safety margin is nice, I feel it is misleading to think it solves the problem. The main problem is RV manufacturers making heavy rigs with little remaining payload capacity so they typically get overloaded and UNDER-tired(too small or weak load capacity tires).
I DO know cold inflation pressure is the standard. As I've said a dozen times before, I am way,way under safety and load limits of RV,axles and tires (both the OE D-range and the current E-range tires at 72 psi).

All I am saying is that as they heat up they will increase in capacity. That is not saying we should drop pressures 20 psi below the safe point, overheat tires and then "hope" they will survive. I am a proponent of weighing your setup if you have ANY doubt or weird tire or wear issues.

[mike5511]

I think I have enough cushion for my trailer: 2 9000 lbs. axles, 4 tires per axle rated at 3640 lbs at 80 psi cold for each. GVWR of 18450, and I'm under that. I may have a failure, but it won't be from being overloaded.

[FastEagle]

Originally Posted by kdauto

I have NOT told people to lower pressures to below what they need for THEIR actual loads and weights. I DID say people should weigh their rigs and adjust accordingly.

When you say actual loads, you confuse the FMVSS tire inflation standard with the commercial tire inflation standard.

The minimum cold inflation according to FMVSS standards is what has been recommended by the vehicle manufacturer for the OE tires. That standard is transferred to all replacement tires.

Inflating tires to the load carried defeats the purpose of load capacity reserves.

For more than 75% of all RV trailers on the road with OEM tires there is no possible tire inflation adjustments available. The trailer manufacturer has already set them at 100% of their capability. To adjust them below what has been recommended violates USTMA inflation standards.

[krsmitty]

Originally Posted by FastEagle

When you say actual loads, you confuse the FMVSS tire inflation standard with the commercial tire inflation standard.

The minimum cold inflation according to FMVSS standards is what has been recommended by the vehicle manufacturer for the OE tires. That standard is transferred to all replacement tires.

Inflating tires to the load carried defeats the purpose of load capacity reserves.

For more than 75% of all RV trailers on the road with OEM tires there is no possible tire inflation adjustments available. The trailer manufacturer has already set them at 100% of their capability. To adjust them below what has been recommended violates USTMA inflation standards.

If I am understanding you correctly....

On my present rig, it came with "D" rated tires which has a cold max PSI of 65. The sticker on the rig says to keep tires at a cold pressure of 65 PSI.

Since I went to "E" rated tires the cold max PSI is 80. I should keep these tire at the max of cold 80 PSI? Since the trailer manufacturer says to keep at max/100%.

[kdauto]

Originally Posted by FastEagle

When you say actual loads, you confuse the FMVSS tire inflation standard with the commercial tire inflation standard.

The minimum cold inflation according to FMVSS standards is what has been recommended by the vehicle manufacturer for the OE tires. That standard is transferred to all replacement tires.

Inflating tires to the load carried defeats the purpose of load capacity reserves.

For more than 75% of all RV trailers on the road with OEM tires there is no possible tire inflation adjustments available. The trailer manufacturer has already set them at 100% of their capability. To adjust them below what has been recommended violates USTMA inflation standards.

Oh brother, I'm about worn out with this and the other tire pressure discussion. I NEVER EVER said to inflate "just" up to the load carried. I always said to add a 10 to 15% reserve.

To put numbers so there is NO MORE confusion and no more back and forth...

An RV owner actually weighs his loaded RV and it bears 4000 lbs on each axle. Since it has 2 tires per axle and for discussion sake the load is perfectly even...each tire needs to support 2000 lbs. Using the actual tire size and load/pressure table use the pressure needed to support 2200 to 2300 lbs per tire. If you want a really harsh ride or plan on loading up/filling more water tanks add more pressure as needed without exceeding max cold pressure stamped on the sidewall.

In this example, if the RV had load range E tires that could theoretically support 3420 lbs at 80 psi (going by memory here, don't kill me if i,m a few lbs off), I see NO need to run 80 psi in all 4 tires.

If you feel absolutely compelled to run maximum psi in all tires no matter the load, go right ahead and jar the rig to pieces, it's your money.

I WILL agree many RVs have very little cargo capacity and I find that shameful. I have 3000 lbs or so with my 32' rig (listed as a 29').

[mike5511]

Ooorrrr, air them ST tires up to their max cold psi rating and take off. More air, less flex, less flex, less heat, less heat, less problems. Replace as needed. Now I'm talking about trailers only. You MH boys have a different situation.

[FastEagle]

Originally Posted by krsmitty

If I am understanding you correctly....

On my present rig, it came with "D" rated tires which has a cold max PSI of 65. The sticker on the rig says to keep tires at a cold pressure of 65 PSI.

Since I went to "E" rated tires the cold max PSI is 80. I should keep these tire at the max of cold 80 PSI? Since the trailer manufacturer says to keep at max/100%.

Was the trailer manufacturer referencing the original equipment tires? Probably so because they seldom, if ever, recommend anything other than the OE designated size.

The tire industry standard for replacement tires requires them to provide, at the very minimum, a load capacity equal to the load capacity the OE tires provided at placard recommended cold inflation pressures. If your LRE replacement tires are the same designated size as the OE tires, their minimum cold inflation pressures is 65 PSI. However, anything above that, all the way to 80 PSI is optional and recommended, providing the valve stems and wheels are rated for the increased inflation pressures.

Some will say to always inflate ST tires to the maximum allowable PSI shown on the tire sidewall. That is most often a personal recommendation unless the tire manufacturer recommends/suggests it.

Remember, once a consumer uses replacement tires that are not recommended by the vehicle manufacturer, all tire maintenance recommendations from the vehicle manufacturer are voided.

[FastEagle]

Originally Posted by kdauto

Oh brother, I'm about worn out with this and the other tire pressure discussion. I NEVER EVER said to inflate "just" up to the load carried. I always said to add a 10 to 15% reserve.

To put numbers so there is NO MORE confusion and no more back and forth...

An RV owner actually weighs his loaded RV and it bears 4000 lbs on each axle. Since it has 2 tires per axle and for discussion sake the load is perfectly even...each tire needs to support 2000 lbs. Using the actual tire size and load/pressure table use the pressure needed to support 2200 to 2300 lbs per tire. If you want a really harsh ride or plan on loading up/filling more water tanks add more pressure as needed without exceeding max cold pressure stamped on the sidewall.

In this example, if the RV had load range E tires that could theoretically support 3420 lbs at 80 psi (going by memory here, don't kill me if i,m a few lbs off), I see NO need to run 80 psi in all 4 tires.

If you feel absolutely compelled to run maximum psi in all tires no matter the load, go right ahead and jar the rig to pieces, it's your money.

I WILL agree many RVs have very little cargo capacity and I find that shameful. I have 3000 lbs or so with my 32' rig (listed as a 29').

Just a little added info. My posts are strictly the way it's supposed to happen. The information I use is from the governing body (DOT/NHTSA/FMVSS) and tire industry standards (USTMA).

Tire industry standards say to NEVER use cold inflation pressures below what has been recommended by the vehicle manufacturer and displayed on the vehicle certification label. Replacement tires must provide, at the very minimum, a load capacity - via cold inflation pressures - equal to what the OE tires provided at certification label cold recommended inflation pressures. (USTMA page #43.... https://www.ustires.org/sites/defaul...TruckTires.pdf ….).