Collision Repair Training | United States
 |
Current Events/News: Advantage Online: 2005 Archives
REMAINING BALANCED
August 8, 2005 - Being well rounded and balanced is what everyone desires in life. Why then would you neglect a troubled tire? As a vehicle is driven, vibrations and noises detected by the vehicle owner can be a nightmare for a repair facility. When wheels are balanced, they actually only remain in a balanced state for a limited time. From the time of initial balancing, tread begins to wear, brake parts wear, and suspension parts constantly wear from stress. The balanced tires gradually become out of balance at different rates depending on variables such as road surface, tire design, and driving habits. The rate the wheel assembly becomes out of balance is small and usually over an extended period of time until one day the owner realizes the vehicle does not ride as smoothly as it did six months or a year ago. To help ensure good ride quality, the Car Care Council recommends wheel balancing when tires are rotated, about every 9,600 kilometers (6,000 miles). Having balanced wheels has many benefits. These include ease of vehicle handling, reduced tire wear, reduced steering and suspension wear, increased gas mileage, and happy customers. In the repair industry, wheel balance can sometimes be difficult. Depending on each situation, especially vehicles that are involved in a collision, vibration control may become a headache for facilities that use equipment with limited abilities. Even though a wheel may be balanced, there may be other problems not detectable, depending on the equipment being used. This article discusses some of the standard and newer equipment available for wheel balancing. Wheel Balancing Equipment There are many different tools, techniques, and opinions within the industry for balancing wheels. This includes common off-vehicle balancing procedures such as static bubble balancing, static spin balancing, and dynamic spin balancing. There are also more sophisticated systems that can spin-balance a wheel and simulate road-force variation type pressure against the tire and wheel assembly. If the equipment in your facility does not remove a vibration problem after repairs, it may be necessary to refer the vehicle owner to a facility that has advanced equipment to correct vibration concerns from tire and wheel irregularities. To help ensure a wheel assembly is balanced accurately, periodic machine maintenance is required. Cones used for centering must be monitored for internal and external wear that may cause deviations in centering when securing the wheel assembly to the balancing machine. It is necessary to have several different centering cones and adapter plates to fit the variety of different wheel sizes available today. If available, use a centering cone with a reduced taper. This will center the wheel more precisely to the balancing equipment. Before balancing a tire and wheel assembly, the tire must be mounted properly. When mounting a tire, first ensure the wheel is not damaged. Use proper tire mounting lubricant and properly seat the bead. Once the bead is seated, inflate the tire to the maximum inflation pressure of the tire, and then reduce the tire pressure to the vehicle maker’s recommended tire pressure. This is done to ensure the tire bead is firmly seated against the wheel edge. Listed throughout the rest of this article, is the general evolution of wheel balancing equipment. Static Bubble Balancing When a wheel assembly is static-bubble balanced, the wheel assembly is removed from the vehicle and set on top of a cone-shaped centering tool with a centering bubble similar to that used on a level. Wheel weights are used to equalize unequal wheel weight distribution. Static bubble balancing can only cure tire hop. Tire hop is caused by unequal weight distribution of the tire and wheel assembly. As the unequal weight distribution in the wheel assembly reaches top, dead center (12 o’clock position), the tire will have a tendency to lift from the road surface. Depending on vehicle speed and weight imbalance, the tire may actually hop and bounce off the road surface. Single Plane Spin Balancing Single plane spin balancing, commonly referred to as static balancing, is also done with the wheel assembly removed from the vehicle, but uses a machine that rotates the wheel. Depending on the type machine used, when the wheel stops turning, the heavy spot of the tire (which is considered to be in the center of the tire, because a static balancing machine cannot determine if the heavy spot is inside or outside of the wheel assembly centerline) will commonly be located at the bottom (6:00 o’clock position) and weight is applied to the top of the tire to equalize the weight imbalance. When doing a single-plane spin balance, dynamic imbalance will not be affected if the weight is placed at the wheel centerline. Static Balancing Considerations A static-balanced tire can only be cured of hop (up-and-down), but not wobble (side-to-side) problems. So even though tire wear characteristics such as cupping can be cured using static balancing, there are other tire balance related problems that cannot be cured by static balancing.
Another consideration when choosing static balancing is placement of the weights. The vehicle owner may want to reduce the visibility of the wheel weights. A common, but incorrect, static wheel balancing method involves attaching weight to the “hidden” inside edge of the wheel assembly. By placing the weights in this location, the weights are hidden, but the dynamic imbalance between the inside and outside edge of the wheel may be increased (see Figure 1). A better static balancing method involves using tape-on weights near the centerline of the wheel assembly. By locating the wheel weight at this location, the weight imbalance of the inside or outside edge of the wheel is not affected as much when compared to the previous balancing method (see Figure 2). In-Motion Two-Plane Coupled Balancing With in-motion two-plane coupled balancing, commonly called dynamic spin balancing, two planes of the wheel assembly are measured as it spins on the wheel-balancing machine. Dynamic balancing measures up-and-down imbalance and side-to-side imbalance. Along with locating up-and-down imbalances, dynamic balancing also determines if the heavy spots on the wheel assembly are inside or outside the wheel assembly centerline, a common cause of wobble. By determining which edge of the wheel assembly the imbalance is on, the proper inside or outside location for the wheel weights (see Figure 3) can be identified. The common way of dynamic balancing wheels is to attach clip-on balance weights to the inside and outside bead edge of the wheel. By placing the weights on the far outer edges of the wheel, less weight is required because weight placement is at the furthest point from the wheel centerline. If the vehicle owner does not want weights exposed on the outer edge of the wheel, the wheel can either be balanced statically by placing the wheel weights only on the inside edge of the wheel, or by dynamic balancing by using stick-on wheel weights placed on the inside surface of the wheel assembly, outside of the wheel centerline. When balancing wheels using this dynamic balance process, some wheel balancing machines provide the option to enter how many spokes the wheel has. Then calculations are made to determine how much weight should be used and placed behind which wheel spokes so the balance weights are not easily visible. Using clip-on and adhesive weights require attaching a clip-on weight to the inside bead edge of the wheel and attaching adhesive weights to the inside surface of the wheel. Adhesive weights should be attached as far outward from the wheel centerline as possible. With this method, the amount of required adhesive weight may be more than what would be required if a clip-on weight was attached to the outer edge of the wheel. This is because of the placement of the adhesive weights in relationship to the wheel center (spindle) requires more weight to produce the same kinetic energy as a weight placed near the outer circumference of the wheel. Using adhesive weights is only done when clip-on weights cannot be attached to the bead edge due to design. Using this method, adhesive weights are attached inside and outside of the wheel centerline on the inside of the wheel assembly. In some situations where extra-wide or oversized off-road tires are used, balance pads may be adhesively attached to the backside of the tread area of the tire. This type of wheel balancing is done typically when large amount of weight is required to balance a wheel assembly. Common On-Vehicle Wheel Balancing Not as well known, or used as much any more, is on-vehicle wheel balancing equipment. Unlike off-vehicle wheel balancing, which only balances the wheel assembly, balancing on the vehicle balances all rotating parts associated with a wheel assembly such as the tire, rim, brake rotor or drum, axle, hub cap, and wheel fasteners. When balancing a wheel assembly on the vehicle, a portable drive motor is used to turn the wheel assembly, a sensor is attached to the suspension to detect vibration imbalances, and a strobe light and meter show the location of the imbalance, and the severity. Advancements in Vibration Control If a tire is spin balanced, it has been corrected for weight inconsistencies. Even though weight inconsistencies have been corrected, there may be high or low spots on a wheel that will translate into up-and-down oscillations. This condition alone cannot be detected by ordinary spin balancing equipment. Along with inconsistencies with the wheel are soft and firm spots caused from ply-overlays within the sidewall and footprint of a tire. The function of a tire is to:
Imagine the sidewall of the tire as a series of little coil springs that compress and extend as the tire rolls across the road surface. Though designed to be uniform, the sidewall of the tire will have some compression deviation when measured at various locations around the tire. With these compression differences, the tire will raise when the stiffer areas of the tire contact the road. Also, like the wheel, a typical spin balancer will not correct this condition for the tire.
How does this affect the collision industry? If a wheel sustains undetectable damage, the wheel may spin balance correctly, but there may still be vibrations while driving. Without identifying the damage, this condition may not be diagnosed correctly. This condition can also occur when installing new tires with undetectable irregularities in tire sidewall compression. To diagnose these conditions, vibration control equipment that evaluates the condition of a tire using a contact or non-contact process may be required to correct a hard-to-find vibration. With this type of equipment, a tire with irregularities (compression) at the sidewall or footprint can possibly be matched to a wheel, and subsequently, a wheel with variations can be matched to the tire. By matching the tire to the wheel, a more uniform ride quality may be achieved. Non-contact vibration control equipment evaluates the condition of the tire and wheel using lasers cameras, infrared and sonar devices (see figure 4). Contact vibration control equipment evaluates the condition of the tire and wheel by using a roller that presses against the wheel assembly as it rotates (see Figure 5). Conclusion Static and dynamic wheel balancing is still performed to correct unequal weight distribution within the tire and wheel assembly, and even though regular spin balancing may provide results that keep customers happy, hard-to-diagnose situations may arise with difficult to diagnose vibration problems. To correct these problems, the aftermarket tool industry has developed a variety of unique equipment to help service facilities achieve a high level of customer service. Depending on each individual situation, the tools used to correct a problem may not always be the same. To learn more information about tire sizes, codes, tread wear patterns, and different wheel balancing techniques, look for the I-CAR program “Tires and Wheels (STE01)” in your area.
|
|||||||||||||||||||
|
|||||||||||||||||||
|
Page Last Revised: |
|||||||||||||||||||
