Balancing tires

Balancing tires

Marion, Doug

High-tech, computer-controlled machines eliminate the guesswork

For decades, vehicle owners have had to contend with tire- and wheel-balance problems and shimmy woes. A good example is a staffer who put brand-new rubber on his Ford dualie, but couldn’t go faster than 60 mph on an 800-mile round-trip trek due to front tire vibration and wheel shimmy. The problem turned out to be two-fold.

The right front tire was incorrectly balanced and badly outof-round. The tire shop technician didn’t spot the tread wobble. Upon return, another technician diagnosed the imbalance but didn’t spot the wobble. After turning the tire 90 and then 180 degrees around the aluminum wheel, the tire still would not come close to being balanced. In this case, the tire was replaced, free of charge.

In another situation, an owner installed new tires in Atlanta, Georgia, and drove to Los Angeles. He readily noticed that the left-front tire vibrated at 65 mph, then bounced like a basketball at 70. The problem turned out to be 3 ounces of outerwheel weight were installed 1/2-inch off center.

Due to modem computer-aided tire designs and internal radial tire technology, tire imbalances are much less common than in the past. On the other hand, today’s tires are being put to extreme weight and distance trials while used on motorhomes, light trucks and trailers. As such, balancing is very important, given that even the best-quality tires and wheels have multiple heavy and light spots that must come together as a “balanced unit” in order to provide a comfortable and safe ride. Most tire companies use electronic spinning machines that flash numbers and bar lines like a small Star Wars invasion which must be properly interpreted by the technician. The following is a basic, easy-to-understand rendition of balancing tires that will give owners important knowledge of the whole process.

TWO-PLANE BALANCING

Speaking in basic terms, a tire-and-wheel assembly is brought to balance by equalizing between two circular planes: inner-and-outer or inner-and-middle. Each plane is a 360-degree circle; the wheel face is the outside plane and the tire’s backside is the inside plane. On custom wheels with no outer balance weight lip, there is a middle plane (center of rim) and an inner plane. All wheels with inside and outside lips or edges are balanced via inner-and-outer planes using clip-on lead weights. Custom wheels, which have no outer lips, are balanced with weights placed on the inner-andmiddle planes. Additional weight is needed on the middle plane because there is more area being balanced. The type of lead weight used in the middle plane is always stick-on type. There are three types of balancing weights: clip-on, stick-on lead squares and stick-on weighted patches. This article deals with clip-on and stick-on. Patch weights are installed inside the tire on the actual casing on oversize, off-the-road, industrial applications.

BUBBLE BALANCING

The so-called “bubble balancing” method has been around about as long as there have been tires to balance. In this method, the wheel and tire are laid flat on a small balancing-point gimbaled pivot with a bubble level at its center. The offbalance heavy side of the wheel and tire drops lower than the lightweight side, and the tire technician simply piles weights on the light side until the tire lays flat and the bubble level is centered. This procedure is simple and effective, although not as precise as modern spin-balance machines. However, smaller shops that can’t afford an expensive spin-balance machine can easily afford the hardware required to effect bubblebalance operations, and in the hands of a qualified technician or an old-timer who’s been at it for many years, the tire can be balanced surprisingly accurately.

BALANCING MACHINE

Today’s modem tire shops use spin-balancing machines, which, as the name implies, spins the tire and reads its state of balance via a computer. As the wheel spins, the machine’s computer picks up the light or heavy imbalance on each plane and notes them in ounces on the screen along with the exact location for new weight placement to correct the imbalance.

All the tire stores we visited used essentially the same type of computer balancing machine, although the brands may have been different. The accompanying photos were taken at America’s Tire Company, Simi Valley, California. The branch’s balancing machine at the time of this writing was a Hunter Engineering DSP 9000. The unit weighs 520 pounds, and it can mount a rim with a width as narrow as 1 1/2 inches to as wide as 20 inches. It can handle a maximum tire diameter of 41 inches and a weight of 150 pounds and can hold an imbalance accuracy to within five-hundredths of an ounce. Plus, its adapters fit just about any wheel imaginable.

For exact inner-and-middle two-plane balancing, the machine measures the distance from the machine to inner plane and from the machine to middle plane using an Inner Dataset Arm. As the wheel assembly spins, each plane’s imbalance is computed and displayed on blinking left- and right-plane Weight Amount indicators, which are next to their respective Weight Position Indicators.

STATIC VERSUS DYNAMIC

There are two types of two-plane balancing: static and dynamic. Static balance corrects the wheel assembly using only a single weight plane, thus eliminating any up-and-down tire imbalance. Dynamic is a dual-plane process where both planes of the wheel are balanced, a system that corrects the upand-down plus the side-to-side movement, which eliminates shimmy. You’ll want your tires balanced using a machine that does both types of two-plane balancing. Most, if not all of today’s computer-balancing machines, balance dynamically.

SPOKE/SOLID WHEELS

What if the stick-on wheel weight in the center is visible between the spokes? Most people don’t like that, so many balance machines feature a computer program to solve this dilemma. On the Hunter balancer, for example, it’s called “Split Weight.” At the touch of a button during balancing, the computer “splits” the needed weight. Half of it goes behind the spoke to the right and half goes behind the next spoke to the left. As a result, no wheel weight can be seen. Solid-faced wheels don’t need Split Weight, as the center plane is hidden.

RED BARS AND-NUMBERS

As the wheel is spinning, the machine’s computer measures the degree of imbalance of each plane and large red numbers appear in the left- and rightplane indicators on the display face. A reading of 1.00, for example, means that particular plane is 1 ounce out of balance; 1.50 means 1 1/2 ounces, 0.75 means 3/4 ounce and 0.00 means the plane is within balance.

When the wheel stops spinning, the left-plane weight-position indicator will glow red in its middle slot. The corresponding balancing weight is then installed at the 12 o’clock position on the inside plane of the wheel rim.

once done, the technician then manually spins the tire until the right-plane weight-position indicator glows in its center-most bar. Whatever the balancing-weight number indicates, it goes at the outer 12 o’clock plane (or middle plane if so chosen). Done deal.

WHEEL-AND-TME RUNOUT

If your wheel-and-tire assembly has a shimmy or shake at a certain speed, runout should be checked. There are two kinds: radial runout, also called vertical out-of-round or egg-shaped, and lateral runout, also known as wobble-it’s the side-to-side movement of the wheel and/or tire. Both can be reduced by either repositioning the wheel on the lugs and/or by turning the tire to a different position on the rim.

Front-wheel runout will result in a steering-wheel shimmy. Rear-wheel runout will be felt in the seat area. if the number reads 2.0 or higher (light-truck tire) on the very first balancing try, wheel runout and tire runout should be examined. If apparent, the technician will often turn the tire 180 degrees on the wheel and spin again. If it gets worse, he’ll then go 90 degrees. if this doesn’t cure the balance problem, the tire should be replaced.

An out-of-balance tire-and-wheel assembly can reduce ride quality, cause the steering wheel to be uncomfortable and can be potentially dangerous. Fortunately, today’s sophisticated machines make short work of keeping tires in within proper specifications.

Copyright T L Enterprises, Inc. Mar 2000

Provided by ProQuest Information and Learning Company. All rights Reserved