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Understanding Tire Ply Rating

This page is designed to give our customers ongoing tire knowledge to give you all the ammunition possible to make an educated decision. Understanding that plies and load capacity are 100% different in properties however co-dependent on each other to make a superior tire is the very first step to comprehending this puzzle.  Let’s start with Load capacity

 

How is the load capacity of a tire determined? 

Let's begin by reminding ourselves that it is not the tire that carries the load, but the air inside it. The tire is just the container for the air. So, if you need to carry more load, you need more air. You might accomplish that with a larger air chamber and in Either way, the tire needs to be strong enough to handle the higher capacity.The traditional ways of defining this are "Ply Rating", "Load Range", and "Load Index".

 

What is meant by "Ply Rating"?

In the early days of bias tires, casing (The main body of the tire exclusive of the tread) strength was built up by adding layer upon layer of cotton fabric. The layers were placed with the thread in each layer at an angle to each other. That added strength, because the tensions would be distributed throughout the layers of fabric. The Ply Rating used to refer to the number of layers of cotton. Since you have to have at least two plies to have a “bias” arrangement, bias ply tires always had an even number of plies

 

 MOTOVATOR – 8PLY STEEL BELTED UTV TIRE

 

 

 

 Is cotton still used?

Cotton went away a long time ago. One of the major improvements was making plies out of nylon. Ply materials continued to improve, especially with the introduction of steel ply materials and radial construction, making the old "Ply Number" less and less meaningful. And that resulted in the newer designation we use today, called "Load Range".

 

What does Load Range really mean?
Load Range indicates the maximum load recommended for the tire. This varies by tire size and inflation pressure: A bigger tire can hold more air and can be rated for a higher load. Also, a given tire size at a higher air pressure results in a higher-rated load.


So what's the difference between tires of the same size but different load ranges?

It's no longer the number of plies. Most radial truck tires, for example, have a total of five plies. There's one steel body ply and four belts under the tread. What is different today is the strength of the steel cables in those plies or the number of cables per inch. We're now at the point where we no longer add more and more plies, but instead, adjust the strength of the entire casing to achieve the desired load capacity.

Will a tire with a higher Load Range last longer?

It might, but it also might not. What usually determines tire life is the rate at which the tread wears and whether or not the tread wears evenly. Compound is also a factor as certain tires are engineered to be used on very specific terrain. Sand tires are a good example of a tire that was NEVER intended to be used on rough terrain or hard-pack. If you use the wrong tire in the wrong environment you will see a dramatic decrease in longevity. As long as the tire has enough load capacity for the maximum load you will be putting on it, buying extra load capacity may not increase your tire life.

Radial vs. Bias Ply, Which is better for your application?

The bottom line is Radial tires flex better absorbs bumps better and they contour to the ground better for a better footprint to the ground.They perform better at higher speeds and rocks crawling situations. If you have a high performance, high horsepower machine and you want a premier tire with the best performance possible you should lean towards a radial. Radials typically cost more so make sure you actually want/need what they offer before you pay a little more for them.


Bias Ply tires are typically used on slower applications where the high performance characteristics aren't needed. Many smaller tire sizes (usually 25 inch and smaller) that are used on older machines are bias ply. They are also more commonly used on the aggressive mud tires where you wouldn't want as much flex. Most of the super aggressive mud tires are bias ply because radial flex isn't wanted or needed.

 

Radial Tire Advantages
  • More efficient fuel consumption

  • Improved traction and flotation

  • Improved cut resistance in the tread area

  • Built to run cooler than bias tires

  • Longer tread life

Bias Ply Tire Advantages
  • Crosshatch construction provides stronger/tougher sidewalls

  • Usually much easier to repair when damaged

  • Due to the design of the tire's construction, bias ply want to roll straight as the trailer itself often does

  • Generally less expensive

  • Potentially smoother ride



To sum it up, we would use radials on any modern SIDE BY SIDE where faster speeds and better performance is expected. We would use bias ply tires on SIDE BY SIDE used primarily in the mud, on the farm, out on the railroad, oil fields, construction sites or other similar applications where you will be driving slower and you don't need the performance that radials offer.