In the irrigation world, there are some choices that need to be made when choosing what tire is the correct fit for your pivot and land.
Before we dive into the advantages and disadvantages of each tire type, it’s important to understand exactly what bias ply and radial means. They two types of tires are constructed extremely different.
A radial tire has cords that run straight across to each bead, perpendicular to the tread face, rather than running at an angle. There are additional plies that run at an angle within the tread face of the tire only, so a radial tire might only have two layers within the sidewall but five or more in the tread face. Radial tires also usually have steel cords. A radial’s construction means it’s usually tough on the tread face but more vulnerable to impact breaks in the sidewall.
With a bias-ply tire, the individual cords that make up each ply or layer within the carcass of the tire run at an angle across the body of the tire from one bead to another. Additional plies within the tire run at opposing angle. The cords that make up the plies in a bias-ply tire are often made of nylon, rayon, polyester, or some other non-metallic material. There are typically multiple layers within the bias ply tire, but the number of plies in the tread face is usually the same as the number of plies in the sidewall. The number of plies will have an impact on the load-carrying capacity of the tire as well as its resistance to impact breaks.
With the basic understanding of bias and radial construction, we can look at situations where each type of tire has an advantage.
Radial Pivot Tires Advantages
Due to the wide, flat profile, the wheel tracks left by radial tires are much easier for tractors and other equipment to drive over.
Radials generally run at much lower air pressure (15-17 psi) than bias ply pivot tires. They can do this because they have strong, flexible sidewalls, they can support the load of the pivot at lower air pressures. This allows more contact area and increased traction in fields that have difficult conditions for the pivot to climb.
Radial tires provide a very smooth tracking and rolling characteristics of a pivot tracking option, leading to less torque being transmitted back into your pivot driveline and tower span structures.
With rugged construction, radials are about 80 percent more resistant to cuts and penetrations.
If a tread face or puncture does occur, a radial tire is much more likely to be repaired and put back into service.
Radials have a much tighter bead to the rim, which reduces the change for “pinch flats” and loss of the bead/rim seal in difficult terrain.
Bias Ply Tires Advantages
Due to their multiple layers, bias ply tires generally have the advantage when it comes to load-carrying capacity. There are a uniform number of plies to support the weight of a pivot in both the tread face and the sidewall.
Bias ply tires can handle a lot of off-road abuse. Sidewall failures are much more common on radials in an off-road environment, puncture resistance is one of the biggest reasons that bias ply tires are the standard in agricultural, industrial, and slow-speed off-road applications.
A puncture with a bias ply tire will most likely stay small, so it can be temporarily repaired with plugs out in the woods until a proper repair can be made. These tears can happen in the tread face as well, rendering a radial tire unrepairable when a bias ply could be repaired and returned to service.
Bias ply tire construction also makes them better suited to more aggressive treads with wider voids between tread blocks, and these tread patterns can clean themselves out more easily than more tightly packed tread patterns with lugs closer together.
Both tires have their strengths and their weakness in other areas. But depending on the type of terrain that your pivot will be running on or the type of job you will be asking the tire to complete your choice may be very tuned in to one type over another. While there is no right or wrong answer to the radial vs. bias ply question, hopefully now there’s a better understanding of where each type of tire performs better so that consumers can make more educated buying decisions.