 Getting The Most From Your Tires
With Active Wheel Balancers
by Vic Cohen
Active wheel balancers have been on the market for about twenty years. Despite their many advantages, most bus converters and fleet operators still balance using wheel weights. The reason may be lack of national advertising or an understanding of how wheel balancers work.
Why Balance?
First of all, why must tire/wheel assemblies be balanced? Many truck and bus operators do not believe radial tires need to be balanced because they are made better than bias ply tires. Actually, because radial tires are made with most of their mass on the outer circumference, even a slight imbalance will be amplified causing high vibration. Any wheel balancer acts as a counterweight to neutralize weight imbalances on the tire/wheel assembly. Wheel weights are placed on the wheel rims after a new tire is mounted. They are positioned as counter-weights, opposite the position(s) of the imbalance. If balanced carefully, they work fine at the beginning, but many factors may again cause the tire to go "out of round."
Some of these factors: (l) Minor damage to wheel, such as dents, during normal vehicle operation; (2) Minor damage to tire, such as cuts or gouges, during normal vehicle operation; (3) Uneven tire wear due to poor alignment or continuous rough conditions; (4) Tire may pick up rocks in tread.
Shortcomings of Static Wheel Balancers
There are other conditions that are not effectively corrected by wheel weights. These are of more concern to tractor/trailer rigs, tankers and auto carriers; still, they are worth mentioning as some of the effects could carry over to a bus conversion. During road operation, the trailer, at the tractor connection, tends to ride up and down. This causes tire bounce on both the drive and steering wheels of the tractor. The tires are continuously being compressed, a condition that eventually leads to tire cupping. A lightly loaded rig will tend to bounce and shake, a condition that is not only hard on the tires, but all mechanical parts and assemblies. You have probably noticed this most when passing or trailing an empty tanker-not only the violent shaking but the noise. Hard trailer braking, causing tire bounce and vibration, leads to further tire wear. Suffice it to say that there are many situations where static tire balancing (weights) can not completely do the job. The reader can probably think of others. Any condition that might change the weight distribution of the tire over the miles and years of driving will not be corrected by static wheel balancers.
Active Wheel Balancers
How much better are the active wheel balancers? Before getting into that, let's find out just how they work and how many different types of active wheel balancers there are. All of them mount so as to turn with the wheel assembly. They are usually in the form of a round metal plate mounted in some manner to the wheel assembly, with a tube filled ball bearings, shot, sand, oil or mercury forming a ring around the outer perimeter. Some wheel balancers are hub mounted, and some are actually in the form of a tire fluid. The only criteria for location is that they become an integral part of the wheel assembly. The wheel assembly may consist of two or even three tires. All the wheels are locked together through the tire lugs. Corrections made by the balancer are for the entire assembly. Only one balancer is needed per assembly regardless of whether it is one, two or three tires. This does not apply to static wheel balancers. In this case, each tire must be separately balanced.
Using Mercury as the Active Element
Balance Masters® of Northridge, California, is the only company that uses mercury as the balancing liquid. These devices are positioned behind the wheel assembly and are adaptable for all vehicles, 3/4-ton and up. President Chris Gamble demonstrated how this balancer helps to prevent tire bounce (one of its many advantages) by filling a tennis ball with mercury and dropping it onto the floor from about shoulder height. The ball did not bounce at all due to the counter force created by the liquid, opposing the attempted upward thrust of the ball. In the Balance Masters® system the mercury is contained in a small neoprene tube forming the outer circumference of the balancer. Because mercury is essentially frictionless, there is no wear on the neoprene tube, and the balancer should never need replacing. Although other products may make a characteristic noise, the mercury device is completely silent. Almost from the moment the wheel starts rolling, the liquid will assume counterweight positions to any tire imbalance. There is no "lumping effect," sometimes caused by shot-filled, hub-mounted and tire-fluid products. The Balance Masters® device is mounted directly behind the wheel assembly. They will reduce or eliminate vibration, increase tire life 50%, eliminate tire cupping, improve braking, roadability, decrease fuel consumption and reduce maintenance cost. Because the mercury active wheel balance lasts almost forever, it is a one-time cost and can be reused when changing tires, wheel assemblies or even vehicles. Another product from Balance Masters® can be attached to the drive shaft. It functions in the same way as the wheel assembly device, eliminating shaft vibration and costly U-joint replacement.
Forgetting about all the mechanical advantages, what this will mean to you and your family will be a better and smoother ride, better road handling, and a less fatigued and more alert driver. If you are bringing along your best china and/or are preparing meals while rolling, and if some family members are sleeping en route, a smoother ride will be thoroughly enjoyed.
Purchasing and Installing Active Wheel Balancers
The Balance Masters® active wheel balancers may be purchased through their office in Northridge, California, or through distributors in other parts of the country. For a list of distributors, or to order, call 1 (800) 786-8324. The wheel balancers come in sets of two with each balancer installed on the right and left wheel assembly per axle. In other words, for a typical bus conversion, consisting of a steering axle, a drive axle with dual tires, and a tag axle, three sets would be required. The probable part number would be SA-303, one set for the steering axle and one set for the tag axle; DT-404, one set for the drive axle dual wheels.
This assumes a 22.5 or 24.5 ten hole wheel for all axles. The listed prices are $189 a set. There is a three-year warranty for any workmanship provided the tire wheel assembly is within the industry standards of 0.125 . Check with the company for more details and possible price changes.
The wheel balancer for the steering and tag axles (SA-303) is actually shaped like a shallow pan. Before installing, remove the wheel/tire assembly from the hub. Any wheel weights must also be removed. Place wheel balancer over lugs with outer ring (which contains the mercury tube) facing inward over the hub. Replace wheel/tire assembly and torque bolts to factory specifications. For the dual wheel drive axle, remove outer wheel and place wheel balancer in front of the inside wheel over the lugs and with the larger of the two holes over the valve stem. Replace outer dual tire/wheel assembly and torque bolts to factory specifications. Consult company for further details. All installation instructions are included with purchase.
The Balance Master drive shaft balancer can be mounted on either end of the drive shaft, or in the middle. It comes in two sections clamped together. To install, simply remove the clamp, place the two sections around the drive shaft at the desired location, and replace the clamp. Again, consult the company for more details.
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