There are three kinds of tire balancer in use in tire and automotive repair shops across the country. These three types and quick explanations of how they work are explained below.
A static tire balancer is mostly obsolete these days. However, the tire manufacturers do still use them to ensure that the unbalance inherent in every tire is within tolerances. This type of balancer works by sensing only what angle off the center line contains the unbalanced portion. Gravity causes a cone the tire sits on to deflect in that direction. On top of the cone is a glycerin filled chamber with an air bubble. This air bubble will deflect in the opposite direction of the unbalance. How much it deflects will determine whether it falls within specifications. This type of balancer can still be found in shops where older, more traditional mechanics can be found.
This is the most accurate, yet most dangerous method of tire balancing. The tire and wheel are left on the car, and a ‘hat’ is placed on the wheel and secured. A motor with a wheel is placed against the tire, causing it to spin. Balance mechanisms contained within the hat determine where the unbalanced condition is occurring. There are six friction rings on a snout protruding from the hat. These friction rings are held lightly by the technician, while he rests a hand against the fender, moving weights inside the hat. When the most ideal combination of inner and outer weights is achieved, perceived vibrations will be minimized. The technician then reads the display, which reads graphically, and applies the required weights in the specified positions. He will then usually spin the tire up once again in order to verify his work. If the proper weights and positioning were used, the least amount of vibrations will occur with both inner and outer indicators reading zero or close to it. This type of balancing is highly accurate because the tire and wheel are spun on the car, allowing any vehicle specific issues to be accounted for, such as an off center lug pattern or hub.
This is the kind of tire balancing machine most commonly found in use these days. The tire and wheel combination is placed on the balancer using a set of cups to center the hub and a locking handle. A technician enters the rim width and diameter and the offset from the side of the machine and pushes the start button. The machine spins the tire up to operating speeds which are usually around 60 MPH. The shaft that the tire sits on is calibrated and runs into the balancer. A computer inside the machine detects the deflection and location of any unbalanced condition in the tire and displays the results on an LED display with lights that move vertically to indicate where the weights are to be placed. The amount of weight required is displayed digitally. Once the weights are applied, the technician spins the wheel one more time to ensure proper weight placement.
A new technology that has recently reached public use is tire balancing beads. These are small ceramic or steel beads which migrate to the opposite side of the tire from any unbalanced areas, counteracting the unbalance.