Out of balance tires take a toll on the machine, the operator, the fuel bill and the tires themselves. However, keeping tires in balance can also be a time-consuming nuisance.
Many truckers and farmers thought balancing beads inside the tire might provide the answer, and they might have for some people.
However, concern has been expressed more recently that they get caught in the tire bead and thus cause leaks. As well, there’s evidence the beads get all balled up in a wad and create more problems inside the tire.
While there’s merit to the basic concept of having loose beads spinning around inside a tire for better balance, practical application of the concept seems to be the ongoing problem. In fact, the concept was first put under scientific scrutiny in the early 1900s, says Robert Coolidge, owner of Centramatic Balance, a Texas-based company that produces on-board balancing systems for cars and trucks.
The Centramatic on-board balancing system does not use external lead weights on the rims, nor does it use beads inside the tire. Instead, it incorporates tiny steel balls encapsulated in a sealed steel ring that fits between the rim and the hub.
“We tried for years to come up with a bead formula that worked. In the end, we never put the product out on the market because there were simply too many problems having loose beads inside the tire,” Coolidge said.
Instead, he focused on using the same principle but with steel balls sealed inside a steel ring that’s filled with oil. The ring fits over the lug studs so the balancing effect constantly applies to the complete wheel assembly, including hub, brakes, rim and tire. As with balance beads, the steel beads flow to the light side of the assembly at road speed.
“When you take off, the little balls just roll around inside the metal ring. They really don’t do anything at low speed. When you hit about 20 m.p.h., centrifugal force gets the fluid and balls to start spinning within the sealed ring,” said Coolidge.
“Below 40 m.p.h., the heavy side of your wheel assembly is turning in a greater diameter than the light side. At about 40 m.p.h. on a truck size tire, you reach the first harmonic resonance. That’s when the diameter of the light side equals the diameter of the heavy side.
“As you go faster than 40 m.p.h., the heavy side starts turning in a smaller diameter than the light side. The light side has a larger diameter. The forces of physics now dictate that the balance balls will go to the light side, thus making the assembly balanced. The whole key is to know how many balance balls to put in the ring for each size tire, and to have them in an oil bath so they can freely move around to find their right place.”
The steel balls look like shotgun shot. The diameter of each steel alloy bead is 0.09 of an inch. They roll around in a synthetic molly fluid that helps absorb vibration and keeps the balls lubricated so they roll around easily.
“The system automatically adapts to any changes in the balance of the tire, wheel, brake drum and hub,” he said.
“Picking up a rock in the tire tread will cause the little balls to re-position themselves to bring the whole assembly back into balance. When the rock pops out, the balls instantly re-balance the assembly.
“Mud or ice on the assembly will cause the balls to change position. As your tires wear, their balance points change. The Centramatic changes with the tire. You can get your tires balanced on a computer balancer, but quite often on big trucks and trailers, the brake drums are more out of balance than the tires and wheels.
“Centramatic Balancers have been shown to increase tire life on steer axles by 25 percent, on drive axles by 35 percent and even more in trailer axles.”
Coolidge said the steel ring idea isn’t new. The first commercial application of the principle came from a company called Permabalance in the 1960s. It sold a car version of the steel balance rings through Sears, MontgomeryWard and JC Whitney. Coolidge bought Permabalance and expanded the product line to focus on trucks from three-quarter ton up to semis.
Centramatic has 3,000 dealers in the U.S. and Canada. Prices are in the range of US$200 per axle.