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Forklift fleet managers have a choice when it comes to tires. They can choose rubber tires or polyurethane tires.
Rubber tires have been with us for more than 100 years while polyurethanes have been widely used for only about 50 years.
Germany was the first to create polyurethane tires during World War II due to the Allied Armies’ efforts to block the regime from access to rubber. As a result, Germany worked on an alternative. During attempts to develop synthetic rubber German scientist, Otto Bayer, discovered a material called polyurethane that has since become a major compound in the field of material handling.
Rubber and polyurethane tires each have their own strengths and weaknesses due to the characteristics of their materials.
As a general rule, rubber tires are used more extensively on propane and internal combustion lift trucks. These trucks can be used outdoors and indoors and rubber tires are preferred because of their softer ride and better traction.
Polyurethane tires, on the other hand, appear on electric lift trucks that are used indoors where the surface is made of smooth concrete. Polyurethane is favored in this application because its load capacity greatly exceeds rubber.
The two types of tires respond differently in situations encountered during normal work activity. This includes:
· Rolling Resistance
· Load Capacity
· Wear and Abrasion Resistance
· Cutting and Tearing Resistance
· High Speed Operation
· Floor Marking
· Response on Wet Floors
· Chemical Resistance
Polyurethane has less rolling resistance than rubber due to its chemical makeup. This is important because higher rolling resistance limits the efficiency of an electric lift. So as a general rule, it is recommended that polyurethane tires be used on electric lift trucks to minimize rolling resistance.
The cushioning ability of a tire is directly related to its durometer or hardness. The higher the durometer number, the harder the tire. What is so important about this is that a softer tire absorbs more impact.
Rubber tires have a range of 67 to 75 durometer while polyurethane tires have a range between 83 and 95. This shows that polyurethane is harder than rubber, so it offers a rougher ride. Assuming that a forklift driver would prefer a softer ride, then under these circumstances, a rubber tire would perform better than a polyurethane tire on trucks that are not electric. If the trunk is electric, then polyurethane tires with a durometer rating of 83 will offer the softest compound that would provide maximum load capacity while minimizing rolling resistance. Polyurethane tires with a durometer rating of less than 83 durometer are not widely available. However, if they were, the softer polyurethane tire will rapidly loose its overall toughness and load capacity.
As lift trucks have been required to handle greater loads, manufacturers of polyurethane tires have developed compounds as hard as 95 durometer to assure increased performance. Although it is true that these compounds can carry greater loads, they offer less cushioning for the lift driver. For forklift fleet managers who are looking for their forklifts to handle a greater load and sacrifice the driver’s comfort for increased productivity, then he should opt for the polyurethane tire. A general rule of thumb is that a polyurethane tire with a durometer rating of 95 will offer about 15 percent more load capacity than a polyurethane tire that has a durometer rating of 83.
The ability to handle a 15 percent greater load may not sound like much. However, it permits a forklift to move tonnage through a warehouse without downtime due to failing tires.
In addition to cushioning, another major difference between rubber and polyurethane are their gripping potential of the surface on which they moves. Rubber tires have a softer tread surface than polyurethane tires. This permits the rubber to offer a broader footprint on the surface than polyurethane. So rubber provides better traction than even the softest polyurethane. In order to compete better with rubber tire manufacturers, polyurethane tire makers have developed a process called “siping” or “routing” that allows them to machine onto the surface of the tire an assortment of tread styles. As a result, polyurethane tires have substantially better traction without sacrificing load capacity.
Polyurethane tires are must more resistant to splitting, tearing or chunking out under load than rubber tires. That does not mean that splitting, tearing or chucking out will never occur on a polyurethane tire. If a forklift riding on polyurethane tires is constantly over loaded, then even polyurethane tires will fail. Overload causes heat on the tires and that causes tire failure.
Wear and Abrasion Resistance
While it is true that rubber offers a softer ride, it will not wear as well as polyurethane. In fact, as a general rule, polyester tires outlast rubber tires by about four times.
Cutting and Tearing Resistance
Polyurethane tires withstand rough floor conditions and debris much better than rubber tires. They do not cut or tear. In fact, items that would commonly cut or tear a rubber tire is embedded into the polyurethane tire tread.
High Speed Operation
Polyurethane tires do not dissipate internal heat very well. In fact, heat is the major enemy of polyurethane. As forklift operators drive faster, heat builds up in the polyurethane and can result in damage to the tire. On the other hand, rubber can dissipate heat and thus can hold up to the higher speeds. This is why it is recommended that internal combustion and propane lift trucks use rubber tires. These trucks generally travel too fast for polyurethane. Electric lift trucks travel at a speed of 6 to 8 miles per hour, which is an ideal speed for polyurethane.
Polyurethane tires will not mark the warehouse floor. Moreover, despite the fact that many polyurethane tires are offered in colors, the basic chemistry used to construct the tire does not permit any colors to mark floors. Polyurethane does appear to leave a marking on the floor, but this is dirt that has been picked up by the tire and then laid back down on the floor.
On the other hand, rubber does leave marks on floors. The markings are caused by carbon black, which is used in rubber. Rubber tires that do not have carbon black are available and will not mark up floors.
Wet Floor Conditions
Warehouses that store produce probably suffer with wet floors. This is because the produce must be kept cool and damp during storage. This particular application can be troublesome for electric lift trucks. Electric trucks using polyurethane tires will slip on the wet surface. Under these circumstances, it is recommended that rubber tires be used. However, polyurethane tires that have been siped will offer better traction without sacrificing load capacity. Rubber tires may offer better traction, but will sacrifice load capacity.
A forklift manager who works in a warehouse that stores chemicals may want to consider using polyurethane tires on his forklifts. Rubber tires that are exposed to chemicals may lose their resistance to tearing and chunking while the polyurethane does not.
However, the fleet manager should keep in mind that such harsh solvents as methyl ethyl ketone, methylene chloride and acids can adversely affect even polyurethane.
Polyurethane tires are more expensive than rubber tires because of the cost of the raw materials needed to make them. Depending on the compound, a rubber tire can cost 25 percent to 50 percent less than a polyurethane tire. The fact that rubber tires can be used for a wider variety of applications and costs less, then rubber will probably always be the dominant product in use in warehouses. However, polyurethane tires should still be used on electric lifts because of the better load capacity despite the higher price.
Although it may be true that the polyurethane tire can cost trice as much as a rubber tire, the polyurethane variety lasts up to four times longer.