Introduction

 

The benefits and value propositions of polyurethane-filled pneumatic tires (commonly referred to as foam-filled tires) and solid tires have been debated many times over the past few years by original equipment manufacturers (OEMs), aftermarket customers, rental companies and tire dealers. It is important to understand that there is a market for both products, but it is difficult to directly compare the two. Each flatproofing solution has strengths and weaknesses and determining the best option is dependent upon the application. Each product will function effectively as long as it is installed correctly and used according to the manufacturer’s instructions. The greatest advantage of polyurethane-filled pneumatic tires over solid tires is the availability of many combinations of tire sizes, tread patterns, polyurethane fill durometers and inflation pressures for the operator to choose from and customize according to each application. It is very difficult for solid tires to compete against this variety of options.

History

Solid rubber tires were first used with heavy equipment in 1868 by Robert Thomson.1 Polyurethane tires were first used during World War II, when German scientist Otto Bayer created polyurethane as a replacement for expensive rubber.2 It was not until 1971, when the company that is now Pathway Polymers invented tire fill (under the brand name TyrFil®), that polyurethane became widely used as a flatproofing solution. This polyurethane tire fill material has seen many further developments and improvements since then, including the development of the AutoFil Recycling System® that recycles 100 percent of the TyrFil recovered from used tires. This continuous improvement of tire fill and the tire fill process has allowed polyurethane filling to maintain its position as the best value proposition for flatproofing tires. This value is the reason that most tire customers continue choosing polyurethane-filled pneumatic tires for their flatproofing needs.

Comparative Overview

Cushioning, Floatation & Shock Resistance A significant indication of the cushioning ability of any polyurethane-filled or solid tire is the durometer, or hardness of the tread rubber and the material that fills the core. A solid or polyurethane-filled tire with a high durometer is harder and absorbs less impact. A tire with a low durometer core is softer and absorbs more impact. Solid rubber tires typically have a tread durometer of 65 and higher, with a slightly softer core. Many solid tires have added aperture holes to produce increased cushioning. Polyurethane-filled pneumatic tires, on the other hand, offer a wider range of core durometers from 8 to 55, allowing the customer to tailor the stiffness of the tire for the application. Additionally, the pressure the polyurethane fill is installed at can be specified to match the application requirements. Thus, polyurethane-filled pneumatic tires provide the operator many options to modify the stiffness of the tire for a more comfortable ride where desired or less deflection where stability is more important. Solid tires, in contrast, offer a limited choice of stiffness. Softer tires absorb more vibration, reducing driver fatigue. Construction and mining machine operators seek as smooth a ride as possible. These operators often prefer polyurethane-filled tires as the comfort and handling characteristics of polyurethane-filled tires are more comparable to those of air-filled tires. Again, polyurethane-filled tires allow for more versatility of use because the core durometer and inflation pressure of each individual tire can be controlled. Because tire fill is available in a variety of durometers, it provides each piece of equipment with the operating characteristics appropriate for each application.

Stability

The stability of a solid or polyurethane-filled tire is dependent on tire construction, tread pattern and stiffness. Solid tires do not offer selection of rubber core alternatives, resulting in a very limited selection of tire stiffness. The available tread patterns of solid tires are also very limited. On the other hand, pneumatic tires offer a much wider variety of rubber compounds, tread patterns and stiffness. This flexibility is an advantage that allows the operator to tailor the polyurethane fill in pneumatic tires to each specific application. Another stability factor to be considered is the density of a tire. Filling a pneumatic tire with polyurethane adds weight and stability to equipment. Rubber is more dense than polyurethane, resulting in added weight and stability. However, a customer must consider that extra weight may be tougher on equipment. The added stability from additional weight may put stress on hubs and wheel bearings, so additional maintenance may be required.

Wear, Abrasion & Durability

The life of a tire depends on many factors, including the application in which the tire is used, the quality of the tire and whether the tire is used according to the manufacturer’s specifications. Solid tires generally have deeper treads and can wear longer than polyurethane-filled tires in the right application. However, the larger variety of tread patterns, sidewall construction and rubber formulation of polyurethane-filled pneumatic tires allow the customer to customize the tire and fill for specific applications and soil conditions. This customization maximizes traction, comfort and tread life,resulting in increased value. When the tread is worn on a polyurethane-filled tire, but the carcass is still functional, the tire can be retreaded. Pathway Polymers’ tests with retreaders has demonstrated that there is no degradation in the polyurethane fill even after four retreading cycles. If the carcass is damaged, a Pathway Polymers dealer with an AutoFil Recycling System can recover the polyurethane fill and recycle it. Some believe that solids are better suited for scrap metal recycling facilities, demolition sites and any application where sidewall damage may occur. However, Corrie DeVilliers with Cool Ideas in Johannesburg, South Africa, has tested both solid and polyurethane-filled pneumatic tires, and has found that using heavy-ply pneumatic tires filled with polyurethane in these applications provides a better value.

Traction

Another difference between solid and polyurethane-filled tires is found in the traction of the tire, which refers to the maximum frictional force that can be produced between the tire and the surface without slipping.3 Due to the wide range of tread patterns, rubber compounds and polyurethane hardness, polyurethane-filled tires have better traction over a wider variety of surfaces and terrain.

Cost

Tires are one of the most expensive maintenance and repair costs on an industrial vehicle. Both solid and polyurethane-filled tires eliminate downtime, thereby reducing costs associated with tire repair. From a pricing standpoint it is difficult to precisely compare the two types of tires as there are many variables to be considered. The initial price paid for tires is generally higher for solids than for polyurethane-filled tires because solid tires require specially designed wheels, as well as special mounting equipment. The replacement costs and availability of these specially designed wheels and mounting equipment should be evaluated when considering total cost. Current aftermarket price analyses show a typical 14.00 X 24.00 solid tire is approximately 60-200% more expensive than a polyurethane-filled tire. Therefore, a solid tire must last at least twice as long to approach the cost savings of a polyurethane-filled tire. (Keep in mind that solid, pneumatic and polyurethane-filled tires are all available in varying grades of quality and durability. The aforementioned comparison was done using similar tire grades for both products.) As with any product, price is only one variable in the value equation. Dealers may purchase a solid tire at an extremely low price, expecting a high return, only to realize that it must be replaced after only a couple hundred hours of use. Similarly, equipment that comes directly from an OEM may have inexpensive polyurethane-filled pneumatic tires that may only last several hundred hours on tough surfaces. However, many tire dealers state that when those tires are replaced with high quality pneumatic tires filled with tire fill, they can last four or more years. Furthermore, several rental customers state that polyurethane-filled tires provide the lowest cost per hour compared to solids. The rental fees that companies charge for similar machines are the same, regardless of whether the tires on the machine are solid or polyurethane-filled. Since polyurethane filled tires are less expensive to buy and maintain, rental companies reap higher profits from rental equipment with polyurethane-filled tires.

Lastly, disposal costs must also be considered:

  1. Polyurethane-filled tires can be retreaded for extra life.
  2. Polyurethane-filled tire carcasses can be recycled after a long, useful life.
  3. The tire fill inside a used polyurethane-filled tire can be recycled by a local tire dealer through the utilization of a tire fill recycling system, whereas solid tires almost always end up in landfills.

Summary

To summarize the text and comparison chart on the previous page, each application requires a specific tread, durometer and stiffness of tire. While solid tires perform well in certain applications, polyurethane-filled pneumatic tires allow the most flexibility, thereby providing the best value proposition for most applications. “The performance of the entire machine and the operator is dependent on many factors,” agrees J.P. Gallagher, of Gallagher Tire, who has been foam filling for over 20 years. “We feel that a foam-filled tire provides the best option to cover the many different areas where these machines operate. We are confident that the tire fill solution is the best option for most machines that cannot afford downtime.” Stuart LaPerle with Preventative Tire Maintenance Group Inc., says that based on his 35 years of experience filling tires, “There is no doubt that solid tires can be effective in certain applications, but polyurethane-filled tires provide the most return for every dollar invested, allowing the operator to utilize the tire for more hours at a lower cost.” Polyurethane-filled tires are the best flat proofing solution available because they provide better cushioning, stability and traction, as well as the lowest cost and highest return on investment over the life of the tire.