By Phil Mosier, Cooper Tire
There is a lot of technology built into today’s commercial tires. They have never been more fuel efficient, nor have they lasted as long. But all that is for naught if the tire doesn’t spin true.
The ultimate success of a tire, and the brand on the sidewall, is how the tire is manufactured and whether it can run true—free from irregular wear. That’s why we, and many others in the industry, take the steps we do to ensure our tires meet exacting specs with tight tolerances. Our goal is to have tires that perform as advertised with no deviation—so tire No. 1 runs the same as tire No. 840. Only then can we take advantage of all the advances we engineer into the tire.
Tire uniformity is something truckers don’t think much about as long as they are rolling smoothly down the road. A non-uniform tire can cause vibrations, pulls and can create noise, which can transmit into the truck through the steering wheel, seats, doors and dash. This creates driver discomfort. Non-uniformity can also create a high level of runout and lead to irregular tire wear patterns like spot wear, out-of-round and erratic wear. For a fleet manager, that’s the pain point in a tire program. Irregular wear erodes the tire’s ability to perform, and when a tire doesn’t run right, fleets look for another that will.
Once you put a tire on a rim, there are other issues related to mounting and balancing—vehicle condition and even how that vehicle is driven—that can have their own effects on tire wear and performance. That helps ensure that every tire that comes off the assembly line can be used to its fullest potential.
The primary causes of non-uniformity in a tire include irregularities in geometry, stiffness and mass, which are defined through a set of measured forces or parameters accepted by major global tire and car makers. These parameters include radial force variation, lateral force variation, conicity, radial run-out, lateral runout and balance. Tire makers worldwide employ uniformity measurement as a way to identify impacts to the ride and handling performance to ensure customer satisfaction.
From Cooper’s standpoint, we consider the standards as minimum requirements, and we strive to exceed those standards by a wide margin. In a lot of cases, we conduct ride studies of our own where our experts quantify what level of runout or balance provides a good, even ride with the least amount of vibration possible.
Long haul steer tires are historically the most difficult to get to wear evenly. Plus, since they’re front-and-center you feel and see any irregularities more so than any other wheel position. It is often said that a tire’s manufacturer’s reputation rides on its steer tire—that’s true.
Inflation pressure checks and vehicle alignment are a few of the key things fleets can control, but the uniformity of the tires plays an important role in how evenly the tires wear. When tires aren’t uniform, there are extra forces put on the tire that make it hop and wobble. This can lead to irregular wear patterns and reduce the overall mileage you get out of the tire. You’ll likely have to retread early.
The process of making a tire involves four major operations: mixing, extruding and calendaring, tire building and curing (where pressure is applied to the green tire in a mold in order to give it its final shape, and heat energy is applied to stimulate the chemical reaction between the rubber and other materials).
Every tire manufacturer has different levels of checks and balances. We, for example, use a statistical-based approach to ensure predictability in the manufacturing process. Every single step of the process has an impact on the quality of a tire. Automation makes the manufacturing process increasingly systematic and reduces the variation in the final product.
After curing, a tire looks like a tire. But there’s one more critical stage before a tire is ready to be sold—inspection and uniformity testing.
Today’s tire uniformity machines are highly specialized, and highly accurate tools designed for optimizing quality control. In our plants, once inspected, tires are mounted on split rims with each side sandwiching together for automated mount and dismount. With the tire inflated to the specified pressure, it is loaded against a test wheel and rotated to collect data on the forces the tire generates as it spins.
Without sounding too scientific, lasers measure the runout in the tread area and sidewall to within a thousandth of a millimeter. From all the info, which is displayed as vectors and waveforms, technicians are able give each tire a pass or fail grade.
The final stop for a tire before it leaves the plant is for the sharp eyes of visual inspectors and x-ray machines.
Ultimately, our goal—and the goal of other top tier manufacturers—is to deliver a safe, comfortable driving experience, with long miles to removal. We continually receive tighter requirements from end users for commercial tires, and that’s why we’re constantly incorporating the latest innovations to improve consistency and uniformity.
Phil Mosier is the manager of commercial tire development at Cooper Tire & Rubber Company. A 20 year tire professional, he is responsible for the design and development of commercial truck and bus tires for the North and South America regions. Mosier and his team have brought to market many successful commercial truck tires in the Cooper Commercial Series and Roadmaster brand tire lines.