P vs. LT Tires
If you are new to over-landing/off-roading and you may want to begin building your perfect rig. The first place I like to start is with tires, and this can lead to some confusion. Tires come in two basic classes, P-passenger tires and LT-light truck tires. Contrary to the names given the tires the vast majority of new trucks and SUV vehicles in the US are sold with P rate tires. I am hoping to write this article to help explain to you how to pick a better set of tires for you rig.
Going back to when we used Bias Ply tires the weight rating system for tire capacity is bases on a letter/number scale: A, B, C, D, E etc. Each letter is 2 ply, so a B tire is a 4 ply, C is 6 ply, E is 10 ply. As a tire goes up in ply rating it can hold more air pressure and carry more weight. P rated tires are considered B rated tires. LT tires begin at C and run up beyond E. Radial tires do not actually add more layers or ply as they did years ago, but construction of the tires can be critical. LT tires are usually made with a more robust sidewall and tread to handle the extra air and weight. This robust construction can be critical in a hauling / off-road rig.
If you look at a standard P class tire and compare it to a LT C rated tire you may notice that the weight carrying ability is close or the same. Tire Manufactures apply a 10% rule with P rate tires on a truck, van, or SUV, which means the P rated tire has to be reduced by 10% in weight carrying ability. So the actual numbers can be deceiving. The reason for this is that trucks tend to carry the majority of their weight in cargo over the rear axle, have a higher center of gravity, and tend to get overloaded more. Passenger cars tend to distribute their weight more evenly over the front and back. Be sure to take this into account if you are looking at tires.
What are the advantages of replacing your tires with a Light Truck grade tire for over-land travel? You will be taking a lot of gear and supplies with you, the weight of all this material will be easier on a LT tire on a long distance travel. It’s better to have an LT tire carrying 80% of its max capacity than a P tire working at 100%. The harder a tire has to work the hotter it will get, this can cause a tire to literally come apart. Another good reason for an LT tire is because of its more robust construction it will be better able to withstand punctures and tears while off-road, and will better handle being aired down for extended off-road trips.
To give an example of this off-road ability I was running a Cooper AT C rated Lt tire, my hunting partner was running a Mastercraft (Cooper made) AT P rated tire. Over a 3 month hunting and trapping season we ran the same logging, fire, and back roads. He had to plug his tires 3 times that season, while I experienced not one issue. He now runs LT tires.
But, there are drawbacks to changing to an LT tire. Robust means more weight. More weight means your engine and transmission will work harder to move the tire, brakes will work harder to stop, and your steering will work harder to move them back and forth. Things will wear out faster. Expect a drop, though slight, in fuel mileage. And, that robust tire will be rougher in ride on the road and off. It will not flex and cushion as much which can stress suspensions and passengers a bit more.
I recommend that if you are trying to choose get on a sites like this and talk to folk who have the same rig, or tire you want to run. Get their advice and opinions. Research your tire brand and look at customer reviews. Also, you will need to deal with a tire shop that will try to tell you that you don’t need a- this grade or that rating. Find a tire shop that deals more in 4×4 off-road vehicles. Do your research and choose wisely for yourself. Good luck, see you on the trail.
Choosing The Right Tire
Everybody needs tires. Whether you drive your vehicle off-road, pull a trailer, or just jam around town, tires are your all-important contact patch to the ground. There are many types of tires available to the diesel enthusiast, so let’s start by decoding the sidewall. After that, we’ll discuss load and speed ratings, as well as tread patterns and sizes. Finally, we’ll talk about usage and taking proper care of your tires.
DECODING THE SIDEWALL
If you look on the sidewall of the tire, you’ll see a series of numbers, like LT285/75R16 or 37×13.50R20 LT-this is the tire size. In either case, LT stands for light-truck tire. In the first example, 285 stands for the tire’s width in millimeters, 75 means the sidewall of the tire is 75 percent the size of its width, R stands for radial, and 16 is the rim diameter in inches. In the second example, the tire is simply 37 inches tall, 13.50 inches wide, is a radial, and mounts on a 20-inch wheel.
If you don’t like the metric version, it can easily be converted to the standard form of measurement. If we first divide 285 by 10, we change millimeters to centimeters, arriving at 28.5 centimeters. Since 1 centimeter equals 0.393 inch, we next multiply 28.5 by 0.393, arriving at the tire’s width of 11.2 inches. Next comes the tricky part. The sidewall is 75 percent of the width in this case, so 11.2 times 0.75 equals 8.4 inches. Since a tire sitting on the ground has a bottom and a top sidewall, we must multiply that answer by 2, arriving at 16.8 inches. Finally, we add the height of the rim (in this case 16 inches) to arrive at the final 32.8-inch tire height.
Light-truck tires are a bit different than regular passenger car tires. The overall tire is much stiffer and heavier than a car tire, thanks to multiple plies (cross sections of polyester, steel, nylon, or armid that run perpendicular to the tread) and can be inflated and run at a much higher pressure, increasing its load capacity and decreasing on-road rolling resistance. Since most diesel owners use their trucks to tow or haul loads, we’d never suggest putting a passenger car tire on a truck-they’re simply not up to the task.
ST (Special Trailer) vs P (Passenger Car) Tires
Passenger car tires achieve comfort in part by making the sidewalls of the tires softer, allowing the sidewalls to flex. Many trailers (especially enclosed cargo trailers and car haulers) have higher centers of gravity than the typical tow vehicle and sidewall flexing in this case can lead to increased trailer sway. The stiffer sidewalls and higher inflation pressures on ST (Special Trailer) tires helps to reduce trailer sway.
The polyester cords in an ST tire are bigger than they would be for a comparable “P” or “LT” tire. The steel cords in an ST tire have a larger diameter and greater tensile strength to meet the additional load requirements. “ST” tire rubber compounds contain more chemicals to dissipate heat under higher loads than tires designed for passenger cars. Trailers will pull better and ride smoother on ST tires engineered and manufactured for trailers.
Trailer Tire Safety Tips
Do not overload the trailer beyond its maximum weight. Extra weight means extra heat, extra wear and could lead to tire failure.
Maintain correct air pressure. Underinflated tires may fail under load. Underinflated tires wear out the tread near the sidewalls prematurely while overinflated tires wear out the center of the tread prematurely. Remember, temperature impacts air pressure. For each 10 degrees in ambient temperature, tire pressure increases by 2-5%. Check tire pressure when the weather changes and when travelling to warmer or cooler climates.
LT tires vs ST tires
Let me share with you some of the key factors to be considered for comparing ST vs LT tires and some insights on what these tires can be used for.
Vehicles and trailers, both have very different driving requirements. A passenger vehicle will need to maintain traction while accelerating, braking, and cornering which makes an LT tire suitable for passenger vehicles. Whereas, a trailer needs to focus on following the tow vehicle and just hold up to the weight that is put on the trailer, which can be best achieved with ST tires
LT tires have softer sidewalls and are meant to flex when rolling over bumps. ST tires have thicker sidewalls compared to the LT tires and are not meant to flex when rolling over bumps. This bump is then transmitted to the vehicle suspension and also to the load riding on the vehicle.
The steel wires used in LT tires are smaller when compared to those in ST tires. The cords used for steel wires in an LT tire are smaller and have less tensile strength as compared to the cords with a bigger diameter in ST tires. ST tires have steel wires with high tensile strength as they are designed for carrying heavier loads.