We've all heard the acronym “KISS,” which stands for “keep it simple, stupid.” This can be a good guideline when we're talking about explaining something to a general audience, or trying to standardize procedures among diverse groups, some of whom we may never actually talk to in person.
But when it comes to product and process technology, KISS may not be the best approach. Here's an interesting example. A friend of mine who's an engineer — but not in the transportation industry — told me he'd read about a new type of tire that's made from chemical ingredients mixed together in the proper amounts and injection molded, similar to many of the plastic gadgets we use every day. His comment reminded me of the once-a-year fly fisherman who really only knows enough to be dangerous! As for my engineer friend, while there's a bit of truth in his information about “plastic” tires, it's not as simple as he made it sound.
Several types of light-duty, slow speed tires molded from plastic materials, notably urethane, are currently available for use on bicycles, wheelbarrows, and similar slow speed applications. They're self-supporting (no high-pressure inflation) and aren't susceptible to punctures, cuts, or snags that can disable conventional pneumatic tires. While they provide some cushioning, they're not energy efficient (high rolling resistance), and don't support high loads relative to their tare weight.
Since the entire structure is made of the same material, traction, weathering ability, cornering forces, and other stability, handling, and ride qualities are severely compromised. Is it possible that R&D will allow gradual up-sizing of this simplified concept to replace the complex truck tires we use now? I don't think so.
Tire makers first experimented with molded plastic tires more than 40 years ago — but the concept was placed on the back burner because performance properties were compromised and the method used to attach the tire to a wheel was not fully successful.
A typical modern radial truck tire incorporates upwards of 25 components, made from 10-15 different rubber compounds tailored to perform specific functions in different parts of the tire. A variety of strengthening and reinforcement materials, such as steel, brass, and nylon, are included. Many engineers consider the pneumatic tire to be the single most complex mechanical component on a vehicle, affecting acceleration, braking, cornering, and fuel efficiency.
A great deal of effort is now being put into improving the tire assembly process, including construction of precision of subassemblies, which are then combined in a final assembly stage, similar to modular building construction. This allows materials with similar physical properties, or components that work together in the different zones of the tire, to be constructed with more reliable dimensional and placement control. These manufacturing advances, as well as development of new material technologies, have led to reductions in overall tire weight, lower rolling resistance, and enhanced casing durability for tires with comparable tread depths.
Injection molding does have some appeal for making individual tire components where a single rubber (or plastic) compound can be used, and dimensions controlled more precisely than with traditional processes.
In the hierarchy of tire engineering, radial truck tires present some of the most formidable challenges. They operate at higher inflation pressures than passenger or light truck tires, and use multiple types of reinforcing materials in complex configurations. Conversion to a more simplified design would be extremely difficult. The highly complex radial truck tires we have now serve us well in terms of reliability and cost-per-mile. I think it's safe to say that simplified designs are not waiting in the wings.