We supply & install Carlisle RV Trailer Tires. They are one of the best rated  trailer tire in the business, we even use them on our own units. 

Some  things you may not know about tires....

Every tire has a birth date—the day it was manufactured—and an expiration date that is six years from that manufacture date. Most manufactures recomend  replacing tires after six years. You can't base your decision on tread wear alone, you will need to visually inspect each tire to look for signs of tire deterioration, such as cracks in the side walls, which can indicate that a tire should be changed. It's best to get in the habit of checking the tires before, and after every  trip.
Although there isn't much you can do about the age of a tire – once it hits that 6-year mark it's recommended to replace the tire regardless of wear – there are some steps that you can take to prolong the life of your tire to ensure it at least reaches its  life  expectancy:

• Keep tires clean by washing them with mild soap and water
• Keep tires inflated to the recommended maximum cold pressure level
• Use tire covers when not in use 
• Take the weight off tires when parked or stored for extended periods of time
• Keep tires away from wet ground as they can absorb water
• Rotate tires occasionally when not in use

What is the proper tire inflation?
Maintain air pressure at the maximum PSI recommended on the tire sidewall. It's best to check tire pressure with a quality tire gauge when tires are cold and in the shade.
Under inflation is the number one cause of trailer tire failure. An underinflated tire creates abnormal tire flexing and excessive heat causing:
- Ride and handling problems
- Decreased fuel efficiency
- Reduction of tire life
Driving on tires with too much air is also not recommended. Over-inflated tires are more likely to cut, puncture or fail by sudden impact.

How do I determine the age of my trailer tires?
Every tire has a date code stamped on the sidewall, which is the date the tire was manufactured. The date code is usually at the end of the DOT I.D. and is a 4 digit number. The first two numbers indicate the week (out of 52) and the last two digits indicate the year. For example, 3409 means the tire was manufactured the 34th week of 2009.
Please keep in mind that remaining tread is not an indicator of tire life as the irregular duty cycle requires that trailer tires sit in extended storage under static load conditions often for long periods without movement or maintenance causing the tire carcass (internal structure) to break down, a condition undetected by visual inspection.

What does “ST” mean?
Trailer tires are designated “ST” for “Special Trailer” tires. Trailer tire requirements differ greatly from automotive or light truck tires. Automotive tires are designated “P” for Passenger or “LT” for Light Truck and are not designed for trailer use. Passenger or truck tires, with their more flexible sidewalls, can result in trailer sway problems. The stiffer, heavy duty sidewalls of ST tires are designed to control and reduce sway problems. The construction, design, materials and testing used in “ST” tires meet the higher load requirements, duty cycles and special demands of trailering.

How fast can I travel on Carlisle trailer tires?
In the past, most trailer tires were rated at 62 or 65 mph. Today, some of our tires are "rated" (speed symbols) at 87 mph (N), some at 75 mph (L), some at 65 mph (J: ST tires) and some at 62 mph (J: non-metric tires).
Please remember that speed ratings are test speeds and not recommended driving speeds. The ratings apply only to the tire itself, and not a particular vehicle. The speed rating does not mean that the vehicle can be safely operated at the tire's rated speed.
We recommend driving no more than 60 mph when towing a trailer. Please always drive at a safe speed and abide by the posted speed limit.

Is it a good idea to install tubes in trailer tires?
Carlisle trailer tires are tubeless tires, meaning they don't require a tube. Our recommendation is that tubeless tires be used without tubes. We do not recommend that customers use a tube to "fix" a flat tire. Flat tires should be inspected and repaired (if possible) by a tire dealer.
Tube-type tires.
When using a tube-type tire, be sure to use the proper size tube, the proper flap and an appropriate wheel/valve stem style with a new tire.

I have two brand new Carlisle tires and two that are about 30% tread. Does it matter which tires are on the front or back axle?
Keep the new tires on the same axle and the two worn on the other. It shouldn't matter if they are positioned in the front or the back. But please keep in mind that tires mounted on the rear axle are likely to wear faster than the tires on the front axle.

Where do I register my new tires?
The tire warranty registration form is on-line at: http://register.cimstireregistration.com/index.cfm?id=carlisle
What information do I need to register? For example, my tire side wall reads: TWI AQ12 DOT AQB5 O512
TWI AQ12 DOT AQB5 O512 means:
- TWI: tread wear indicator, which is marked on the upper sidewall
- AQ12: mold number
- DOT: Department Of Transportation
Please register the information following the DOT mark which is "AQB5 0512".
- AQ: Manufacturing plant code
- B5: Manufacturer specific tire size code
- 05: Production week
- 12: Last 2 digits of the year of manufacture (2012)
There is room for 12 digits on the registration form but Carlisle only uses 8 digits.

Carlisle states that your trailer tires exceed DOT requirements. What do you do to exceed DOT requirements?
Trailer tires are held to the FMVSS119 standard for DOT. The endurance test under this standard is typically either 34 hours or 47 hours depending on the size of the tire. The load during the test varies from 66% up to 114% per the DOT requirement. Carlisle always extends the test after meeting the minimum endurance requirement for passing DOT by increasing the load to 130% and continuing the test. Our standard production checks are set to meet approximately twice the mileage required by DOT on the endurance wheel. We also have development standards that will exceed our standard production checks to insure that our product is robust enough so that we well exceed the DOT requirement at all times.

Should I choose 8 ply over 6 ply tires?
The 8 ply (Load Range D) will carry more load than the 6 ply (Load Range C) so it depends upon the weight of your trailer. Never exceed the maximum load rating stamped on the tire sidewall or the maximum vehicle load rating, whichever is less.

Trailer Tires Side Wall Specifications
The side wall of a trailer tire provides specific information regarding the size and style of the tire. For example, ST175/80D13C means:
- ST - Specialty Tires for trailer use only.
- 175 - The maximum width of the trailer tire is approximately 175 millimeters at its widest point.
- 80 - The height of the sidewall is 80% of the width, in this case 140 millimeters.
- D - (For diagonal) shows that this is a bias tire. The belts on this tire run diagonally from bead to bead or at about 45 degree angles to the center line of the tire. If your tire shows the letter R, your tire is a radial tire. The belts on this tire run radially from bead to bead or at 90 degree angles to the center line of the tire.
- 13 - Indicates this tire fits on a 13 inch diameter wheel.
- C - Is the load range. Typically a "C" load range is equivalent to a 6 ply rated tire, "B" is a 4 ply, "D" is an 8 ply and "E" is a 10 ply rating.

Should trailer tires be rotated?
Trailer tires can be rotated when on a tandem axle to achieve move even wear across the set of tires.

Can trailer tires be plugged and patched?
A dealer may be able to repair a trailer tire with a puncture. Some tires are not repairable based upon the size and location of the puncture.

What is the maximum psi limitation for your trailer wheels?
Max air capacities are typically a function of the tire, not the wheel. Unlike tires, the load rating of a wheel is not generally dependent on the operating pressure. The wheels themselves are manufactured and tested to a load rating (without consideration of pressure) and can safely support that load. As long as the load is within the limits of our wheel's load rating in pounds, our product will perform as expected.

original  Source (https://www.gallaghertire.com/about/carlisle-st-faq)