Tire/wheel balancing is a service that most tire dealers offer because it helps tires ride smoother and last longer. It can also add some much-needed profit to your bottom line.
Proper balance is especially important with light truck/SUV tires especially LT-sized units ®€“ because of their larger diameter and heavier tread and casing. The larger the diameter of the tire and the heavier the tread and casing, the greater the force any imbalance has as speed increases. Consequently, a light truck/SUV tire may require heavier counterweights than a passenger tire to offset an imbalance.
On the other hand, the larger the diameter of a tire the fewer rpm it has to make at any given speed as it rolls down the highway. This lessens the effects of imbalance somewhat. Even so, most light truck/SUV tires should not require more than a few ounces to achieve proper balance.
Only a 0.25-ounce of imbalance can produce a noticeable vibration in some vehicles. It depends on the sensitivity of the steering and suspension, the type of wheels (alloy wheels tend to be more sensitive to imbalance than steel wheels because of their rigidity and lighter weight), vehicle weight and speed.
If your balancer tells you a tire needs a lot of weight say six or more ounces ®€“ something may be wrong. The tire or wheel may be out-of-round, may not be properly matched, or the wheel may not be centered on the balancer arbor.
Dirt, nicks and wear on the mounting cones or wheel may be causing misalignment and inaccurate balance readings. It’s also possible your balancer may be out of calibration.
Rebalance Your Balancer
One way to improve balancing accuracy and repeatability is to use precision machined flange plate lug adapters instead of centering cones. Flange plate adapters center the wheel on its lug holes rather than the center hole. Lug adapters are expensive, but eliminate many of the mounting problems associated with cones.
If you suspect an out-of-round tire or wheel, check tire and wheel runout with a dial indicator. Both radial (vertical) and lateral (sideways) runout should be checked anytime a vehicle has a speed-related vibration or shake.
Light truck/SUV tires can usually tolerate more runout than passenger tires. Chrysler, for example, says radial runout on Ram and Dakota pickups and Jeeps should not exceed .060 inches. This compares to about .030 inches for a typical passenger tire. The limit for lateral runout on trucks varies from .060 to .080 inches, which is double the limit for most passenger tires.
If a tire and/or wheel has too much radial runout, you can match mount the tire by rotating its position on the rim to align the tire’s high point with the wheel’s low point. Most tire brands indicate the high spot on their tires with a colored dot. Wheels are usually marked in a similar fashion; if the wheel is not marked, match the tire’s high point with the valve stem hole in the wheel.
This high/low matching trick should reduce overall runout, as well as the amount of weight needed to balance the tire and wheel assembly.
Effects of Force Variation
Another problem that can cause unwanted vibrations is radial force variation a point of strong argument across the industry today. A tire can be perfectly balanced and round as a cue ball, but still shake due to force variation. In a nutshell, force variation ®€“ both radial and lateral ®€“ can be caused by inconsistencies in the tire, the wheel and even the brake rotor or drum.
With regard to the tire, these inconsistencies are caused by variations in materials assembly, heavy or weak splices, ply arrangements, weight imbalances, and variations in spring rates around the tire.
Because wheels have virtually no spring rate, their contribution to force variations is limited to weight imbalances, mis-centering or poor machining/finishing. Because they are often not high tolerance products, brake rotors/drums can be the culprit due to weight imbalance, inconsistency, uneven wear and warping.
Force variation has long been understood by the tire industry, and has become more prevalent as passenger vehicles have gotten smaller, lighter and more finely tuned. The problem is how to measure it.
One balancer manufacturer has a unit that presses a roller against the tire as it turns to simulate a rolling load on the tire. The roller can not only detect an out-of-round tire, the maker says, but also tell you where the stiffest spot in the tire is, which can then be match-mounted to the wheel’s low spot to compensate for radial force variation. The result, they say, is a smoother riding tire and fewer comebacks.
As a rule, tire/wheel assemblies should always be balanced anytime a tire is replaced, repaired or remounted. Most dealers recommend balancing a new set of tires when the tires are installed, but some overlook the importance of rebalancing tires that have been demounted for repair and remounted on the same rim.
Marking the tire position and indexing it to the valve stem on the wheel is no guarantee the assembly will be in proper balance when the tire is returned to service. Why? Because balance changes as a tire wears, and there’s no way of knowing if the tire was in proper balance before it was removed. So rebalance anytime the tire is removed from a wheel.
Rebalance as Tires Wear
Tires also need to be rebalanced periodically to compensate for natural tread wear. As the tread wears, the distribution of weight around the circumference of the tire changes. This can affect both static and dynamic balance, leading to unwanted vibrations and shakes. Ideally, tire balance should be checked anytime the tires are rotated or at least every other time. But since most motorists don’t rotate their tires regularly, most tires are never rebalanced unless an obvious vibration develops or the tire is replaced.
There’s also the issue of cost. Some dealers include free balancing when a customer purchases a set of new tires. Others charge anywhere from $8 per tire up to $15 or more. Over the life of a tire, this expense can really add up, so few motorists are willing to spend additional money having their tires rebalanced.
One alternative here is to offer your customers a balancing product that goes inside the tire to provide long-lasting benefits. For many years, fleet owners have used powder-based balancing products inside their over-the-road medium truck tires.
The dynamics of rotation cause the weighted powder to cling to the inside of the tire in such a way that it equalizes balance. Extensive testing and real-world use shows that not only does this help maintain balance for the life of the tire, it also results in a smoother riding tire. Other similar products that use glass beads or liquids also claim to provide similar benefits.
The point is, stress to your customers the real tire-life and reliability benefits to keeping their tires balanced. It’s a great profit center waiting to be tapped.