As truck suspension systems become more sophisticated, driver expectations for ride quality continue to rise. The little shake or shimmy that was overlooked or accepted years ago is no longer tolerated.
Commercial tire dealers must be able to diagnose and correct even the smallest ride complaint. But it's equally important to minimize the chances of an imbalanced assembly.
According to some tire and wheel manufacturers, a properly serviced assembly should not require any external balance because the level of precision and uniformity that goes into building the modern tubeless radial truck tire has never been better. In fact, when properly mounted on an aluminum disc wheel, certain assemblies will have very
little, if any, run-out.
Since it's virtually impossible for dealers to measure the run-out on every mounted assembly, many of them incorporate some type of balancing program for customers who are particular about ride quality. The best practice is to use a systems approach that includes several steps. Here's a look at them.
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Clean and lube
Before attempting to mount any truck tire, it is important to thoroughly clean the entire rim surface from rim flange to rim flange. Any dirt, debris or corrosion on the bead seating surface can cause the tire to seat improperly. In most cases, the combination of a wire brush and a shop rag will clean both steel and aluminum rims. If corrosion is severe and has resulted in excessively deep pitting, the wheel should be removed from service and scrapped.
With the fitness of the rim established, the next step is lubrication. Traditionally, the tech wipes the beads with tire soap and then mounts the tire. In higher volume operations, techs lubricate and mount numerous tires, sometimes 20 to 30 at a time. When those 20 to 30 tires are left to sit around for 20 to 30 minutes before the beads are seated, the chances of a mismount increase significantly.
Selecting the proper lubricant is another crucial component of a tire uniformity and balance program. The best bet is to look for products that say "rubber lubricant" on the container with no petroleum-based substances.
If you're wondering about the presence of petrochemical products, ask for the MSDS, or Material Safety Data Sheet, and look at the contents.
Paste and solid lubricants are becoming more popular in some areas as they nearly eliminate the chances of any moisture in the tire, provide a certain level of corrosion resistance on the rim, and don't dry out as fast as liquid lubricants.
Lubricating the beads is only half the battle. Far too many truck tire techs fall short of completing the job by failing to lubricate the rim. The bead seat areas just below each rim flange and the drop center should be lubricated prior to mounting the tire. However, when dry balancing compounds are used, lubrication of the rim surface can result in some operational issues. Check with the manufacturer.
Some tiremakers also place markings on the sidewall to indicate the light spots on the tire. Generally speaking, a yellow dot represents the light spot and it should be aligned with the valve stem. The red dot usually represents the high spot and should be aligned with the dimple on a steel rim or the valve stem. (If both dots are present, consult the tire manufacturer for its guidelines.)
This practice is known as match mounting. When techs properly align the red and yellow dots during the mounting process, the foundation for a uniform and balanced assembly is established.
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Front row seating
There is no longer any art to seating the beads on a tubeless radial truck tire. With the solution to the problem permanently found in the various types of portable air blasting devices, the age-old methods of exploding vapors will thankfully remain age-old. However, there still are some issues that need to be addressed.
The first one is the position of the tire when the beads are actually sealed. All tire manufacturers recommend that the assembly be sealed horizontally so the beads can be evenly seated on the rim. When the beads are sealed in the vertical position, gravity naturally forces the wheel to the ground and the conditions for the creation of a mismount are better than ever.
From the tire manufacturers' perspective, it's called "concentric bead seating" and it's determined by measuring the distance between the molded rib on the sidewall and the rim flange. If the distance varies by more than 2/32nds of an inch, then the tire is not properly seated and all the wheel weights and balance products in the world will not stop the vibration.
It's important to note that the tire should be placed in a safety cage once the inflation pressure has reached 5 psi.
Inflation matters
Any discussion on tire uniformity and balance must also stress the importance of the correct cold inflation pressure. Under-inflated and over-inflated tires are more prone to problems like irregular tread wear patterns that lead to vibrations.
At installation, improper inflation pressure may not have an immediate and noticeable effect on ride quality, but as the tread starts to wear unevenly, the driver will begin to notice a slight vibration that eventually becomes so severe that the tire needs to be retreaded or replaced even though it was perfectly balanced.
Balancing products
There are two types of balance, static and dynamic. Static imbalance occurs in the vertical plane and is often referred to as "hop." Dynamic imbalance occurs in the horizontal plane and is referred to as "wobble."
The goal of tire balancing is to apply weight to the areas opposite the heavy spots in the vertical and horizontal planes to eliminate the hop and the wobble.
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Here's a look at three different methods:
* Computer balancers consist of two components: the cabinet which houses its electronics, and the shaft that rotates after the tire and wheel assembly is installed.
By measuring the vibrations in the shaft, the computer can determine how much weight is required in specific locations to achieve a static and dynamic balance. The tech then takes lead (or equivalent) wheel weights and installs them on both rim flanges or on the inside of the rim with tape weights at the recommended points. If the numbers on the machine come up "000" after installing the weights, the assembly is balanced.
There are some definite advantages to this approach. First, the tire is almost perfectly balanced at the recommended cold inflation pressure so if the pressure is maintained and the vehicle is mechanically sound, the tire should wear evenly until it's time to be retreaded or replaced.
Second, the technology essentially provides a "high speed" balance that reduces the chances of a vibration during highway operation.
And finally, the state of balance is not subjected to external forces like moisture and corrosion, which also means it does not adapt to any changes.
* Dry balance compounds. There is a wide variety of compounds, designs, shapes and installation methods, but the basic principle of using centrifugal force to offset any imbalance or radial force variation is the same for everyone. Many of these products have thankfully gone to the "throw-in" bag so technicians don't have to battle the cloud of dust that coats the beads when using an air-blaster.
The primary advantage of these dry balance compounds is that they constantly adjust to the condition of the tire while it's in service. As tread wear patterns set in and various cold inflation pressures are experienced during operation, the product just shifts to another spot when needed.
Of course, they are somewhat dependent on a dry interior so excessive moisture inside the tire can reduce the effectiveness.
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* Mechanical balancing devices. These often resemble a hollow tube filled with a certain number of metal balls. The device is placed between the wheel and the hub or drum and works on the same principle as the dry balance compound by utilizing centrifugal force to offset any heavy spots in the rotating assembly.
Some owner-operators are big fans of these products. The only major concerns are, of course, the condition of the device so the metal balls don't become projectiles during service and the fact that an additional piece of metal between the wheel and the hub or drum can have consequences with bolt tension loss if the surfaces are not clean and smooth.
As mentioned earlier, the greatest balance technology on earth cannot offset the effects of a mismounted tire. When the tire is properly mounted, seated and inflated, there should be a fairly consistent degree of uniformity that does not result in a ride complaint. And it's also important to note that the tire sometimes is not the source of the vibration; the truck's front end and undercarriage components should also be carefully inspected. The tire is not always the source of a ride complaint.
However, as suspension systems become more sophisticated, even the slightest imbalance in the tire and wheel assembly will be felt by the driver, so commercial tire dealers need a solution to the problem.
Regardless of the technology that is chosen, dealers must understand that a quality tire mounting and inflation program will pay maximum dividends in the long run.
This article is part of a regular series on tire industry-related topics written for Modern Tire Dealer and its Commercial Tire Dealer section by Kevin Rohlwing, senior vice president of education and technical services for the Tire Industry Association.
