LT tires

[sambam]

I'm beginning to search for new tires to replace my Marathons and have noticed a good number of you use LT tires as opposed to ST's.
The question I have is the load range of these tires. I have looked on several manufacturers web-sites, Goodyear, BF Goodrich, Maxxis, Firestone, to name a few. None of these have LT tires with a load rating high enough for my camper. In fact I didn't even see any with load ratings as high as these Marathons. Maybe I'm missing something, but my Montana can't be that much heavier than any of yours, so what gives? I am also interested in the G614, but being a weekend warrior, I'm thinking I don't need all that, at least 'til I retire and begin to fulltime. My axles are 7000 lb. so would like to have at least a 3500 lb. load range. I am trying to work a deal out with GY for the G614's in exchange for my tires. If they work with me, I'll most certainly go that route, but if not, I need a back-up plan. So, where is my thinking going wrong about these LT's?

[fauch]

Speed rating vs load rating.
We use up the load rating of an ST tire with highway speeds

An LT tire OTOH at say a 106 mph speed rating, has a greater load capacity at 65mph than the load rating printed on the tire, which is commensurate to it's speed rating.

maybe this will help:
http://www.bridgestonetrucktires.com/us_eng/real/magazines/98v3issue4/v3i4Tech.asp

[Art-n-Marge]

It's about what's called reserve capacity. I believe you wanna get in touch with DQDick who oftens posts information describing this very well when this subject comes up. Or get in touch with LonnieB, MOC's tire expert (manages a Tire Rack in New Mexico). I don't have the answers off the top of my head, but there's some folks to contact.

As for STs, Maxxis or Sailun are possibilities.

[steelpony5555]

Your thinking is not wrong. Most LT tires are are rated for 3042 lbs and ST tires are at around 3400 lbs I think. But LT tires being "passenger" vehicle tires are held to a higher testing standard then ST tires. The ST tires are rated at the max they can possibly care but the LT tires are rated with a cushion built in. Now I did read this somewhere I just forget where. But if you have 7000 lb axles I would go with the G614 tires. If your trailer had Marathons on it the LT tires in my opinion and my opinion only would still be a step up. But to be in spec I would put tires on that have the numbers to match your running gear......

[DQDick]

Give me an email at dqdick10432@yahoo.com and I'll send you an article that's been around the internet for years that will make the issue clearer for you.

[fauch]

That article might be valuable for all of us.
The reason there are so many trailer tire failures is related to speed:load rating. If we payed attention to and heeded the labeling on tires this never ending discussion would get simpler. Please see article in link in my last post above. The chart illustrates the effect of speed on capacity. E rated LTs do not reach their capacity until 106mph. G rated Sts capacity are maxed at 75 mph. There is a near linear correlation between capacity decrease per speed increase. THIS IS the reason that there are so many trailer tire failures. So to respond to Dave's OP question again, please see the chart in my post above and it will help you to understand why a 3042 lb. rated LT tire (@ 106 mph) may be a better choice than a 3500 lb. rated ST tire (@75 mph)

[Phil P]

Hi

I am not sure what you all are talking about.

My commercial truck tire dealer has “G” rated 3750 lb LT tires.

Phil P

[Chip]

Shouldn't the first question be "what does the rig weigh fully loaded?"

[WeBeFulltime]

quote:Originally posted by Chip

Shouldn't the first question be "what does the rig weigh fully loaded?"




In my opinion the weight that really matters is the total weight of both axles while hooked to truck and ready to travel. That is the weight that the tires are supporting.

[1retired06]

You were looking for an option other than G614s. For the past ten years I have run Firestone TransForce LT tires on all three of my Montana's without a single blowout or issue.

[sambam]

quote:Originally posted by 1retired06

You were looking for an option other than G614s. For the past ten years I have run Firestone TransForce LT tires on all three of my Montana's without a single blowout or issue.


Those tires are in the discussion should I go with LT's. I have them on my truck and am very happy with them.

[DQDick]

In my opinion the weight that really matters is the total weight of both axles while hooked to truck and ready to travel. That is the weight that the tires are supporting.
[/quote]

I believe in taking it a step further. Since we have large pantries and refrigerators, in our case file cabinets and a whole lot of tools, and we have large basements to carry all kinds of stuff, I'm concerned with the weight on each individual wheel. You can get that information from any of the Escapee parks that do weighing and sometimes from the folks who travel to rallies and events.

[mhs4771]

Just be advised, if you go to a reputable Tire Shop there is a strong possibility they will not install tires with a lesser capacity than what's on the sticker on the front road side of the Monty. Now there are many shops will not look at the sticker and will install what ever you want.

[Art-n-Marge]

The weight rating to use for getting the correct tire is the wheel rating on the ends of the axle. I have 6,000 lb axles, then each wheel must be rated at a minimum of 3,000 lbs. If you only use the actual weight at the scale and each tire only weighs 2,500 lbs, then you can never carry another thing because that object could put your wheels at a new weight. Instead you want to use the maximum rating of the wheel and ensure you have some margin. I do currently have Marathons rated over 3,400 lbs so I not only satisfy the axle rating, I have some margin. My tires are approaching 6 years old and I will be replacing them prior to our next outing (probably in summer).

DQDick does have a great recommendation, that you must also know your individual wheel weights (only a scale can measure this), to ensure your rig wheel's are each below the rating. For example on my rig, all weights are about 2,700 lbs except the passenger rear at 2,400. It's been a while since I've been to the scales and hope to do this prior to getting my next set of tires, just to ensure things are still okay. Knowing ratings is required, but knowing your actual weights are within your ratings is even more important.

[steelpony5555]

What mhs4771 says is important because you may have a tire shop in your town that is ok with putting lower rated tires on a 7k axle. But if you are on the road and have a problem, you may have trouble finding a tire shop that will help if they see 3k lb tires on a 7k lb axle...... May not happen but have seen stranger.....

[sambam]

Thanks you all for your responses. I have a clearer understanding of load ranges and reserve capacities now. Dick sent me some info and I checked out the link from fauch and it makes some sense. But, how do you know what your reserve is at a given mph? OK, so you buy an LT tire with a speed rating @ 106 and a load range of 3042. How does that compute to 60-65 mph, which is where I'll be with the trailer on the back? Is there a formula? Blind faith? It seems a little ambiguous to me. I'm not trying to discredit the science, just trying to understand it. You all seem to know a bit about this so I'll keep digging 'til I get it, too.

[rohrmann]

There's no worry if you just go with G614's. Makes the weight rating and you can go 65 mph all day long, and you should be able to get service from most tire places anywhere across the country. Just keep them at 110 psi and you're good. Weekend warrior or full time, the damage from a failed tire costs the same.

[Bigsky3625RE]

We upgraded to 17.5" wheels and GY G114 tires. Lots of safety margin. One less thing to worry about.

No need to wait to be a fulltimer to be safe.

In my mind, these tires are carrying more than a trailer. They have the potential to cause harm if they fail. To our family and others.

Travel safe.

Ken and Jackie

[mach111]

OK, no body has mentioned rims here. OP has '10 Monty. He needs to ensure his rims can handle 110 PSI. Probably can since unit is 2010. OP needs to inspect back side of rim for his specs. My 09 has 80-85 Psi rims. Being held to only 85 PSI limits the weight rating. According to my individual loaded wheel weights Michelins XPS and my 85psi rims can handle the weights. Yes I do have 6k axles.

One needs to start with the weights of each wheel loaded and make the decisions. Love to follow these tire threads for I learn more info each time.

[JandC]

quote:Originally posted by rohrmann

There's no worry if you just go with G614's. Makes the weight rating and you can go 65 mph all day long, and you should be able to get service from most tire places anywhere across the country. Just keep them at 110 psi and you're good. Weekend warrior or full time, the damage from a failed tire costs the same.


That says it all. Our first Montana was used and already had the G614 tires, but the new one did not leave the dealership without having new G614's installed to replace the junk factory supplied tires. I didn't want to add that cost when purchasing the new unit but didn't feel I had any choice. IMHO the two most important things that can't fail when towing these weights are brakes and tires. Why not go with a proven tire that will probably never fail?

[fauch]

This is the DOT regulation go-to for tire installers.
My train of thought is to not have the tires be the weak element in the calculation.
My old 2955RL had D load rated tires on this tag. I kept E rated LTs on it. With 6000 lb axles, the E rated LTs surpassed the axle rating.

[IMG]http://i58.tinypic.com/2yvoqr5.jpg/img]

[dieselguy]

Once again I'd like to remind (all) people here and not just the Keystone owners with mega trailers of this reoccurring issue. Although the OP has one of the heavier trailers and the G614's could possibly be the way to go for him ... there are many who follow the MOC who own one of the many smaller trailers of which G614's are way more tire and cost way more money than you really need. It also needs to be pointed out that many of us are no where near the GVWR during our normal use. Take the time to weigh your trailer and you may see this very point. It continually irritates me to hear the blow and go that G614's are the only round piece of rubber that will suffice to support your rig. Many of us with the smaller rigs use and will continue to use LT's with equal peace of mind. If you're going to swear by something that is not all encompassing ... at least include a disclaimer.

[moutard2]

I think you've hit a number of nails on their heads with your comments dieselguy. You make some good points!

[sambam]

Precisely why I'm questioning. Until this thread, I knew nothing about LT tires, reserve capacity and speed ratings. Now I know a little. I know I can tow comfortably with the right LT tire. I also know that I don't travel anywhere near my GVW of the trailer. Getting it weighed is on the list, but right now I know there is no way I'm close. Will the G614's work for me? Of course, but some LT's will too. I am not fulltiming and don't want an expensive tire like the G614 rotting in the driveway 45-50 weeks a year. That's my point. If I can safely run a less expensive tire for the next 3-4 years, I can upgrade to the G614 at that time when I'm ready to do some serious travelling. I also know that some of these LT's aren't much less expensive than the G614 (XPS Rib). If Goodyear will give me some credit towards my Marathons, the 614's are a slam dunk. If not, I have other options. Thanks again to all that shared their opinions. Nothing gathers a crowd like a tire thread!

[steelpony5555]

Here is that article about how they test these tires...yes it is long but some good info. This is why I say if your trailer had Marathons on that LT tires are an improvement and will most likely be fine.....




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.

[bncinwv]

Wonder if there are any legal issues that one should consider in their choice of ST vs LT, trailer weight and axle ratings? Ouch! that is gonna leave a mark![}:)][}:)][}:)]
Bingo

[mach111]

Sambam

My Michelins XPS Ribs cost was much less than the Goodyear G 614's. Do some shopping. I agree with your facts that our Monty will be safe with the LT tire. As of now we are still weekend rvers for a few more years then we will be serious rvers upon retirement.

diesel guy--Well said Sometimes overkill is a waste.