Easy As Popcorn
I’m all for making things idiot proof. Just the other night I was cooking popcorn in the microwave, and I started thinking about what that particular appliance has done for food preparation. Twenty years ago, if I wanted popcorn I had to cook it on the stove or a special popping device. If I used too much oil, the popcorn ended up greasy. Too little oil and it burned, and the whole house would smell.
Life is so much easier maybe “convenient” is a better word ®“ that I don’t have that kind of pressure.
The current process of making good popcorn at my house involves unwrapping a bag and placing it in the microwave. Then I simply touch a button marked “Popcorn” and minutes later I have a bowl of perfectly popped corn, ready for butter and salt. Most of the kernels are popped, there’s minimal grease, and clean up is a snap. Idiot proof.
So what does popping popcorn have to do with lead weight balancing? If you think about it, the electronic computerized balancer is like a microwave oven. Slap on the tire/wheel assembly, set the dials and install the weights where you’re told.
It doesn’t take a high degree of training to push buttons and reach numbers. Of course, you’ll have to hit your fingers a few times to get the hang of installing wheel weights, but the pain will speed the learning process.
On the outside, a computerized balancer appears to be idiot proof. But, wait a minute. If I don’t put the bag in the middle of the microwave and make sure the right side is facing up, I won’t get my bowl of perfect popcorn. So maybe it’s not all that easy.
Even the most idiot-proof device requires some common sense, especially when it’s in the hands of a real idiot. I shouldn’t need a doctorate in agricultural engineering to make popcorn, but I have to at least be able to follow some simple instructions.
Unlike a microwave, a computer balancer is made to measure radial and lateral variations on a tire/wheel assembly. It assigns specific amounts of lead weight to exact locations around the assembly to eliminate hop and wobble. The maximum amount of weight that can be applied to balance a truck tire/wheel assembly depends on the size of the tire and the particular application.
If you make your living driving a truck, a ride disturbance or vibration is like a nagging toothache it just never goes away. Diagnosing the problem involves a lot more than throwing an assembly on a computer balancer and tacking on weights until the numbers read “0.00.” In order for static (radial/hop) and dynamic (lateral/wobble) balance to occur, the tire must be concentrically seated on the wheel.
When a tire is perfectly centered on the rim, there is minimal runout to the assembly assuming the wheel is perfectly round. Any variation in a concentrically seated tire and wheel often goes unnoticed by the driver, especially on drive and trailer axle tires.
Concentricity is determined by measuring the distance between the rim flange and the guide ribs on the sidewall. If the variation in that distance is more than 2/32-inch, the tire is mismounted.
A tire that is not centered on the rim possesses substantially more variation, which results in a vibration. You cannot correct an improperly seated tire with lead weights, dry compounds, golf balls or other devices. And it will not correct itself after it returns to service, either. In other words, a poorly seated tire will always result in some form of ride disturbance until it is properly seated.
All on the Bead
Before we talk about correcting this problem, let’s look at some methods for preventing it all together. One of the most common causes for a non-concentrically seated tire is debris on the bead or the bead-seating surface on the wheel. All corrosion and build-up must be removed, and the area should be lubricated with a vegetable-based tire lube. Believe it or not, failing to lubricate the rim surfaces constitutes a violation of OSHA Standard 29 CFR 1910.177.
Another cause of an improperly seated tire is seating the beads when the assembly is in a vertical position.
Gravity naturally causes the rim to fall, which can lead to problems if the rim surfaces and beads areas are not properly cleaned and lubricated. Laying the assembly parallel to the ground with the bottom of the tire bead in contact with the bottom rim flange is the best position to ensure concentrically seated beads.
There are all kinds of methods for seating tire beads parallel to the ground. Some time ago, I came across a homemade device that solved a number of problems. Snider Tire in Greensboro, N.C., took an old 22.5×8.25 demountable rim and welded two pieces of angle iron across the rim flanges to act as stops. They simply lay the tire on the rim and roll it into a horizontal position. It’s quick and easy. But best of all, you don’t have to lift the tire or wheel.
Correcting mis-seated tire problems is easy. Completely deflate the assembly and break down both beads. Sometimes it’s necessary to rotate the tire on the rim 180Þ, especially if a “balanced” tire/wheel assembly continues to cause vibration.
Make sure the bead seating surfaces are clean and lubricated. And re-check the rim flanges to make sure there are no dents or dings preventing the beads from seating. Seat the beads with the tire lying parallel to the ground, and place it in a safety cage for inflation after the beads are seated.
The maximum tire inflation pressure outside a safety cage is 5 psi, and the maximum tire pressure for seating beads in a safety cage is 40 psi. If the beads are not seating at 40 psi inside a safety cage, the tire should be completely deflated, thoroughly inspected and properly remounted. Remember that a non-concentrically seated tire will not correct itself in service.
Don’t Rely on Balancer
Even a good computer balancer cannot solve every anomaly. If, after you’ve balanced a tire/wheel assembly, a certain amount of vibration still exists, you can try some of the dry balancing products offered by companies like International Marketing. These reportedly work well in resolving ride vibration concerns but only after the tire and wheel have been mated and balanced properly.
Using a computer balancer to balance a truck tire/wheel assembly is a lot like microwaving popcorn it’s idiot proof if you follow a few simple rules.
If you start with a concentrically seated tire and properly set the readings on the machine, the balancer will show you exactly where to place weights and how much weight ®“ to arrive at static and dynamic balance.
If the amounts of weight are too severe or the assembly appears to wobble or hop while on the balancer, then it needs to be deflated, inspected and remounted.
It’s as easy as making popcorn, but only if you put it right side up and hit the “popcorn” button instead of the one marked ®potato.®
Kevin Rohlwing is director of training for the International Tire & Rubber Association (ITRA), and this article originally appeared in ITRA’s Commercial Tire Service publication.