Wheel Balancers - Learn More

Wheel Balancing Fundamentals

The Need for Wheel Balancing

Out-of-balance wheels cause vibrations which are uncomfortable to a car’s occupants, may adversely affect handling and can cause premature wear on a number of under-car suspension parts. These include ball joints, shock absorbers, wheel bearings and the entire steering linkage assembly. Out-of-balance wheels can also produce abnormal tire wear as well as a ‘jumping’ effect that can dramatically reduce a vehicle’s adherence to the road. The importance of properly balanced wheels has increased in recent years due to the trend toward front wheels drive and lighter, more fuel efficient vehicles.

A wheel balancer is used to reduce this vibration source to a level which will not accelerate vehicle wear nor be perceptible to the vehicle’s occupants. The balancer accomplishes this by determining how much weight and where this weight should be placed on a wheel to offset the existing imbalance. The correct position is one directly opposite ( 180 degrees ) from the imbalance.

Other Sources of Vibration

There are many other potential sources of vibration in a vehicle besides imbalanced wheels. These additional vibration sources must be explored if a customer complains of continued vibration after wheel balancing has been performed.

Additional Imbalanced Parts

Any vehicle part which reciprocates (pistons, connecting rods) or rotates (drive shafts, flywheels, brake rotors, or engine parts) is a potential vibrations source.

Wheel Run-out

A balanced wheel can still be a major source of vibration if run-out is present. A rim that is poorly made, is not perfectly round or has been bent will result in run-out. Likewise, a tire that is improperly mounted or has tread irregularities. Such as flat spots due to skidding or hard spots from faulty manufacture can cause vibration.

Run-out is a significant problem. Barely visible run-out of a few hundredths of an inch, such as wobble when the wheel is spinning or a rim that is not precisely round, will cause more vibration then a weight imbalance of several ounces. Wheels should always be viewed carefully during the balancing procedure check for run-out. If a new tire appears to have a large imbalance check for run-out. In fact, balancing a wheel with large run-out may actually worsen the vibration.

Faulty Tire Construction

During tire construction, the multiple plies of reinforcing fabric can overlap inconsistently, shift during tire molding or cause the stiffness or the tire to vary along the tire tread. Unlike tire run-out, this type of defect may not be visible; however, it will cause vibration because the stiff section has the same effect as a high spot on a tire with run-out.

Water in Tires

Water inside the tire will cause erratic and unreliable balancing. Two sources are excess water used as a lubricant to mount the tire and water carried in compressed air. Tires should also be checked for other internal foreign matter.

Sympathetic Vibration

Non-rotating parts can sometimes produce a ‘sympathetic vibration’, whereby road irregularities or the vibration of rotating parts cause non-rotating parts to vibrate at their resonant frequency. This type of vibration can be recognized as the vehicle speed and vibration intensity increase but the vibration frequency remains constant.

Balancing Tolerance

The goal of wheel balancing is to reduce the imbalance to a level which cannot be felt by passengers or cause accelerated wear of mechanical parts. These criteria are usually met by balancing to within ¼ ounce (or 5 grams) on small cars, ½ once on full size cars and ½ to ¾ ounce on light trucks. There are no significant benefits to balancing finer than ¼ ounce of 5 grams and virtually no wheel weight manufacturer markets weights less than these amounts.

        * Accu Turn Balancers round imbalances to the nearest
        ¼   ounce or 5 grams in STANDARD mode and 1/10 ounce
        or 1 gram   in FINE mode.

Remount Error

Remount error occurs whenever part of a rotating assembly is removed and reinstalled. The principal cause of balancing remount error is the slight variation in the seating of the wheel against the cone and hub which occurs each time the wheel is remounted. The largest contributors to remount error are irregularities on the rim and hub mounting surfaces (dirt nicks, burrs or rust) and imperfections in the rim centering hole.

For example, if a balanced 14” wheel weighing 35 pounds is removed and remounted on a balance, a host of factors could cause the wheel to shift two or three thousandths of an inch (0.003”), about the thickness of a human hair, and produce a ‘new’ imbalance in excess of ¼ ounce.

The above example illustrates the principle mechanism which causes remount errors. Slight remount errors are inevitable, but if they are within the ¼ to ½ ounce balancing tolerance described previously, the remount error does not represent a problem because the wheel is balanced to within the tolerances required by the vehicle.

Static and Dynamic Balance

There are basically two wheel balancing techniques:

Static balancing (Single Plan)

Simplest – usually done on an inexpensive “bubble” balancer
cannot detect all the forces causing wheel vibration.
Primarily detects up and down vibration

Dynamic balancing

Most common form of imbalance found on today’s vehicles.
Detects multiple components of imbalances on a spinning wheel
(up and down as well as side to side vibrations).
Can only be corrected by using a computerized dynamic balancer.