KISS Tiremaking
We’re all familiar with the acronym "KISS" ®“ Keep It Simple, Stupid. It’s generally good when instructing a large audience or trying to standardize procedures among diverse groups. KISS helps people remember detailed procedures, routines and sequences.
However, KISS doesn’t always work when product and process technologies are involved. I was reminded of this vividly in a recent conversation with an engineer who works outside the automotive and transportation industries.
He had read about a new type of tire consisting of chemical ingredients that are merely mixed together in the proper amounts and injection molded. It sounded easy. "Maybe we can make tires the same way we make the multitude of plastic gadgets we use very day," he suggested.
His tale reminded me of the once-a-year fly fisherman, the one who has a somewhat clouded idea of what fly fishing is about, but only enough to be dangerous.
It is true that there are currently several types of light-duty, slow-speed tires available that are molded from plastic materials, notably urethane. These are designed for use on bicycles, wheelbarrows, forklifts, and similar slow-speed applications.
They are self-supporting (no air inflation) and have the advantage of not being susceptible to punctures, cuts or snags that can disable conventional pneumatic tires in damage prone service. They provide some cushioning, but are not energy efficient due to their high rolling resistance. And they do not support high loads relative to their tare weight at highway speeds.
Since the entire tire structure is made of the same material ®“ no belts, no carcass plies ®“ traction, weathering ability, cornering forces and stability issues like handling and ride qualities are severely compromised.
The question remains: Will continuing research and testing allow this simplified, single-compound tire concept to replace the complex automotive and truck tires currently in use?
Early Experiments
That’s not to say tire manufacturers haven’t experimented with molded plastic tires, or even injection molded rubber tires. They have been since the late 1950s or early 1960s. Goodyear, Firestone and others produced a number of these as "test tires" and evaluated them on automobiles. Some were made of a translucent red material and fitted with lights inside the air chamber to draw attention to the tire’s unique material and construction. If you remember these, you’re an industry veteran!
Ultimately, the concept was placed on the back burner because too many performance properties were compromised by these single-material tires. Moreover, the method of seating or attaching the tire to a wheel was not fully successful.
Still the idea of a single compound tire is tantalizing. Today, a typical radial truck tire incorporates approximately 25 individual components. This includes 10 to 15 different rubber compounds tailored to perform specific functions in different working zones of a tire. To this, add a wide variety of strengthening and reinforcement materials, such as steel, brass, nylon, polyester and other synthetics.
Not surprisingly many car and truck engineers consider the pneumatic tire to be the single most complex mechanical component on the vehicle (even if OE pricing is constantly squeezed). Tires significantly impact acceleration, braking, cornering, fuel efficiency and on-road reliability, and are considered integral to overall vehicle design.
Tiremaking Efficiency Focus
At the moment a great deal of tiremaker effort is being concentrated on the tire manufacturing process. The heart of this push is to find more efficient ways to more accurately place all of the tire components more precisely in their assigned locations.
Computers now have the lead role in tire development and testing, so it only makes sense that they should also lead actual production. In fact, lasers, robotics and computers are being employed in new ways to improve the tire manufacturing process. The goal is to be able to deliver tires that provide consistent, highly predictable performance.
One method of achieving this is to construct a number of precision subassemblies, working in concert in the final assembly stage. Think of it as being similar to modular building construction. In this way materials or components with similar physical properties would work together in different zones of the tire, such as beads, sidewalls, shoulders, crown or tread.
In this way, a tire could conceivably be constructed with more reliable dimensional and placement control. Recent advances in these manufacturing processes and new material technologies have allowed reductions in overall tire weight, lower rolling resistance and enhanced casing durability for tires with comparable tread depths.
Challenges Remain
The concept of injection molding holds special appeal when and if a single rubber (or plastic) compound can be used. There is little doubt that finished tire dimensions can be controlled more precisely via injection molding than with traditional extrusion processes. At least one major manufacturer has experimented with injection molded pre-cure treads for retreading. This process eliminates the splice common to other pre-cure treads and generally offers improved dimensional control. This, in turn, can translate into better ride, less vibration and longer miles-to-removal.
Radial truck and military aircraft tires present some of the most formidable challenges for updated technology applications. Both operate at higher inflation pressures than passenger, light truck or even standard medium truck tires, and both utilize multiple types of reinforcing materials in complex component configurations. Both, also, would seem to be most difficult to convert to a more simplified design.
Tire manufacturers have a long history of methodical development and engineering, a painstaking technology evolution that yields few dramatic breakthroughs over time. It’s been that way from the beginning.
The key to tire design and production revolutions isn’t in any research and development lab or budget limitation. Rather, it is a function of customer acceptance, which, at least on the commercial side of the business, is a function of cost-savings and on-road performance validation.
When will the highly complex radial truck tire feature single-compound construction? Certainly it won’t happen until such tires can deliver the reliability and cost-per-mile expectations the industry demands. Today, such simplified designs are a long way off. But tomorrow?
