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Old 10-11-2006, 07:59 AM   #15
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7.00 x 15 hard to find but still available

I have seen 7.00 x 15 Toyos on a '76 Tradewind. I think they're actually LTs, like the original Airstream tires were.

Yokohama or Bridgestone may also supply 7.00 x 15s, if you are interested in having the correct size for the trailer. You would have to ask a knowledgeable dealer to find them.
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Old 10-11-2006, 08:38 AM   #16
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I don;t think the speed rating is determined by the "ST" label
  • Speed rating: VR (V-rated radial)
  • In this case, V identifies a speed rating above 149 mph.
  • Table 1 lists speed ratings.
  • The R means the tire is a radial. Virtually every new tire is a radial, unless you have a special tire for a classic car or a racing car.
Table 1: Speed Rating Designations
Speed Designation
Maximum Speed Rating
N
87 mph
P
93 mph
Q
99 mph
R
106 mph
S
112 mph
T
118 mph

Why Use An "ST" Tire
  • "ST" tires feature materials and construction to meet the higher load requirements and demands of trailering.
  • The polyester cords are bigger than they would be for a comparable "P" or "LT" tire.
  • The steel cords have a larger diameter and greater tensile strength to meet the additional load requirements.
  • "ST" tire rubber compounds contain more chemicals to resist weather and ozone cracking.
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Old 10-11-2006, 09:44 AM   #17
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A Bit of the Difference is

Quote:
Originally Posted by golddigger
I have always wondered: what is a trailer tire? What makes it different from, say, a truck tire? Why would I not want to put an LT on a trailer? Could I swap the Good Year Marathon load range D 225/75R15 for 225/75R15 LTs with load range D?
Trailer tires and wheels are subjected to side loading. This explained to me was when we turn tightly towing the trailer, more force is exerted on the tire and wheel in a direction that it is not necessarily rolling in. ie (scrubbing)Sideways forces are not applied to the tow vehicle in the same manner. When our tow vehicles are turning, there is no wheel or tire "scrubbing" therefore our tires are "rolling." ST or special tires are designed for these sideloads. LT light truck tires are not. Also, If you look at the weight ratings for the LT tires, they usually carry a lot less weight than the trailer special tires.
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Old 10-11-2006, 10:27 AM   #18
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Quote:
Originally Posted by Lipets
I don;t think the speed rating is determined by the "ST" label
  • Speed rating: VR (V-rated radial)
[LIST]
Bob,

I believe the speed ratings that you listed (and there are more) apply only to "P" or passenger tires. I have not seen any of those speed ratings on an LT or ST tire.

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Old 10-11-2006, 12:18 PM   #19
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Y'all can do what you want.

Quote:
Originally Posted by Lipets
I don;t think the speed rating is determined by the "ST" label
Having been in the tire and automotive industry for more decades than I care to think about, believe me when I say an ST tire is speed rated for 65 miles per hour, NOT 112.
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Old 10-11-2006, 01:02 PM   #20
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Isn't the ST tires on all new A/S's, hard to believe they are limited to 65mph?

Not that I doubt what your saying, but where is this stated by tire manufactures?
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Old 10-11-2006, 01:24 PM   #21
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Another good read

In order to select the proper load range, you must first weigh your trailer fully loaded. This means full of water, LPG and gear. Go to a truck stop or public scale and weigh the entire rig. While you are there, weigh each axle separately. This will let you know if you have exceeded the tow rating of your tow vehicle or are overloading one of the trailer axles.
There are other considerations in picking ST tires. For the trailer tires to manage the weight, all must be identical. Do not mix bias and radials tires. What's more, the load range and size of each tire should be the same. And each should have the same amount of tread wear. This becomes critical when replacing a tire.
When replacing a single tire, always run the same size outside diameter tires on the same axle. A smaller- diameter tire will carry more weight, and may become overloaded.
After a blowout on a tandem-axle trailer, you should replace both tires on that side. The remaining tire was likely subjected to excessive loading and, as a consequence, may fail in the near future.

MAINTENANCE TIPS
When a trailer is in long-term storage, there are steps you can take to add life to the tires.
  • Put the trailer on blocks to take weight off the tires.
  • Lower the air pressure.
  • Keep the tires covered to protect them from the sun's ultraviolet light.
When taking the trailer out of storage, make sure there are no cracks in the grooves and no wire showing. Cracks in the sidewall could indicate interior damage or separations in the tire.


MAXIMUM PSI?
As indicated earlier, maximum load range is attained only when the tire is at its maximum air pressure. Yet, should you maintain maximum pressure even if you are towing below the load range of the tires?

Tire manufacturers differ on this point. "You should maintain the maximum pressure at all times," says Carlisle's Garbarino. "There is no advantage to taking air out of the tire. With maximum pressure, the tire will perform and wear better, and you will get better mileage. Reduce the psi, and you compromise the functionality of the tire."
Titan Tire's Evans feels differently. "If you want a little softer ride, drop the psi a bit," he says. However, he cautions that: "They have to know the actual load."
"Trailer owners should set the pressure according to the load," says Goodyear's Fry, who provided the tire pressure vs. load chart that accompanies this story. "Yet, this is not easy to do without weighing the trailer."
"Once the weight is accurately determined, the pressure should be set when the tire is cold, not when it is hot."
All the manufacturers agree on one point: If you do not know the exact weight of your trailer, keep the ST tires at the maximum cold psi.
Based on updated thinking, there are ultimately three keys to avoiding tire trouble while towing: (1) Make sure your rig is equipped with the proper tires: (2) maintain the tires meticulously: and (3) replace trailer tires every three to five years, whether they look like they're worn out or not.
As my grandfather used to say, take care of your equipment, and it will take care of you.
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Old 10-11-2006, 01:40 PM   #22
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Here's what Tire Rack has to say about LT tires:

"LT = If a tire size begins with "LT," it signifies the tire is a "Light Truck-metric" size that was designed to be used on vehicles that are capable of carrying heavy cargo or towing large trailers. This includes medium and heavy-duty (typically 3/4- and 1-ton load capacity) pickup trucks, sport utility vehicles and full-size vans. Tires branded with the "LT" designation are the "little brothers" of 18-wheel tractor-trailer tires and are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo."

In the trucking industry they distinguish between steering axle and non-steering axle use. The side loads on a tire used on a steering axle are far more severe. The oft repeated arguement that our RV trailers have some huge side load and are subect to "scrubbing" that doesn't exist on the TV doesn't hold up. The rear axle on a car has the same "scrubbing" action as a trailer. Far worse if it's on a dual axle configuration or attached to a limited slip differential. Plus, most people tend to corner much faster when they're not towing and a 1 ton pick-up with a giant camper is as heavy and has a higher CG than just about any Airstream.

The "superior construction techniques" in ST tires is likewise just marketing euphimisms for cheap construction. They increase the diameter of the cords to get a higher max inflation pressure and increased load capacity. Look at an ST tire and an LT tire of comparable load and the LT tire will be heavier, more expensive and meet far stricter standards. LT tires are derated because they're going to be used for carrying "live cargo". That's one of the reasons the ST tires have a high rated load capacity for the price.

Again from the Tire Rack:
Speed Rating

"Today, the only tires that continue to include the speed rating "in" the tire size (P225/50ZR16) are Z-speed rated tires. In this case, following the two digits used to identify the aspect ratio are the letters ZR to identify the tire's speed rating (Z) and its internal construction (R). Since 1991, all other speed ratings are identified in the tire's Service Description

A Service Description identifies the tire's Load Index and Speed Rating. Service Descriptions are required on all speed rated (except for Z-speed rated) tires manufactured since 1991.

The significance of the speed rating is that it's a measure of how well the tire disipates heat. The hotter the outside temperature or the faster you go the lower the load carrying capacity of your tires. In addition LT tire usually carry UTQG markings. "

All "ST" tires have a maximum speed rating of 65 mph. It's a well disguised fact because if dealers and manufacturers made the facts readilly available they'd have a hard time selling tires. Remember that on a hot day your max speed goes down and tire degredation from heat further diminishes the capability of the tire.

LT tires are available in 7.00X15R but they're hard to find. I'd love to get a Toyo in that size. I was just in a local Les Schwab dealer inquiring about this since they're the largest Toyo dealer in the west and I've always been happy with their service. It appears that the Toyos in this size are no longer imported to the US although they're still very common in Asia. Likewise Michelin seems to have stopped importing this size. Yokahma is the only choice I've found other than private lable brands.
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Old 10-11-2006, 01:51 PM   #23
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Quote:
Originally Posted by Lipets
Isn't the ST tires on all new A/S's, hard to believe they are limited to 65mph?

Not that I doubt what your saying, but where is this stated by tire manufactures?
http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos;jsessionid=FjdZTL21TVhG3d YkGLRd84gQMBwyXLNbGGm2WwQt0yS8TbNm0DF5!1088327042! NONE
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Old 10-11-2006, 03:18 PM   #24
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Quote:
Originally Posted by lipets
Isn't the ST tires on all new A/S's, hard to believe they are limited to 65mph?


If only it were that GOOD!
  • Time and the elements weaken a trailer tire.
  • In about 3 years roughly one third of the tire's strength is gone.[read, your speed/load rating is less]
  • Three to five years is the projected life of a normal trailer tire.
  • It is suggested that trailer tires be replaced after 3 to 4 years of service regardless of tread depth or tire appearance.
Mileage
  • Trailer tires are not designed to wear out.
  • The life of a trailer tire is limited by time and duty cycles.
  • The mileage expectation of a trailer tire would be 5,000 to 12,000 miles.
5-12k miles, that's great for driveway sailors but doesn't cut it if you plan any long trips in the heat of summer. I can't find the specifics of the test for ST rating but it's been brought up before that the temperature the 65mph rating is derived at is significantly below the actual conditions many people encounter. UV and concrete slabs aren't the only reason trailer tires "rot". Heat literally destroys them from the inside out. Think about it, how many car tires crack and bulge after 3 years and they don't even have the "extra chemicals to resist weather and ozone cracking." Sure storage is hard on tires but collector cars or abandon vehicles out in a field don't have this problems to anywhere near the extent seen with trailers.
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Old 10-12-2006, 02:21 PM   #25
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All this tire talk and I blew the right rear out on my dually yesterday. Thank goodness the inside was there to keep the rig steady. 1 1/2 hours and road service had me going with new tires on the RR. I now have a spare that is only 4 years old.
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Old 10-12-2006, 02:36 PM   #26
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What is the Right Size Tire?

1. Goodyear Marathons are Speed Rated to 65 mph. Go to the Goodyear web site:

http://www.goodyear.com/rv/pdf/marat...nfo_032806.pdf

to read a statment by Goodyear concerning this fact.

Here are the load inflation tables on the Goodyear site:

http://www.goodyear.com/rv/pdf/rv_inflation.pdf

2. According to the poll on this web site, "Your Towing Speed"

http://www.airforums.com/forums/f232/poll-43-your-towing-speed.html

51.65% of the respondents tow their trailer at 65 mph or faster. 65 mph leaves you with 0.00% safety margin on the tires design loading and speed.
I wonder if that could be the reason for so many ST failures? To this add:

"Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is necessary to increase the cold inflation pressure by 10 psi above the recommended pressure for the load".

"Cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire."

Great, now we are supposed to overinflate the tire iif we are going to overspeed the tire. Why, so we will stand a better chance of hearing it when it goes (smart remark) or to stiffen the sidewalls to reduce the increased flexing of the sidewalls thus reducing the internal heat build up which will ultimately result in the failure of the tire?


3. There are 16 inch tires avaliable(G.B.Goodrich Commercial T/A LT225/75R16 LRD, 110/107Q) (Q=99mph) that are the same Outside Diameter (OD) as the original 7.00/15 Michelin XCA that came on a lot of Airstreams and the same width as the ST225/75R15 Marathon that Airstream recommends. With the proper wheel, the 16's work nicely.

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Old 10-12-2006, 04:01 PM   #27
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Hi AlbertF--7.00x15LT D Goodyear "Work Horse Rib" bias construction are easy to find if you go to WalMart. They have them for $107.20. Load rating is 2045# @ 65psi--Frank S
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Old 10-13-2006, 12:58 AM   #28
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Many thoughts on tires as always ,65mph on marathons period .Thats it.
Well documented fact . The heat is what kills and too much load on the tires
cause many failures .

Scott
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