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Perfect Circle?: Out-of-Round Tires, Though Rare, Deserve a Second Look

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We didn’t say much when they took the fat out of our ice cream and cholesterol out of our potato chips. Even the sweet taste in our iced tea probably isn’t sugar. Sometimes we don’t pay much attention to the changes taking place right under our noses.

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Take out-of-round tires, for instance. We used to grind, slice and peel them until they were ‘perfectly round’ and still spend hours trying to zero out the balancer. Today, an out-of-round tire is on the endangered species list. You can find one, but it sure isn’t like the old days.

Why? Because vehicle makers instruct – demand, rather – that tiremakers produce OE tires to meet specific dimensions and weight requirements, along with longevity expectations, speed ratings and handling performance.

That’s what the world’s tiremakers, especially those with automated facilities, are up against. They are providing OE and replacement tire customers with very round tires, built to very tight tolerances. Where the human touch, with its many variables, once ruled, robotic arms and sophisticated assembly procedures have taken over. Tire uniformity is now quantifiable in most tire plants, says one engineer.

Less Than Perfect

Problem solved, right? Well, not quite. Occasionally, a tire line can experience problems with being out-of-round before the problem is located and solved. So, the issue is not completely behind us. But, our best guess is that out-of-round tires will be history in about five years.

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Not long ago, high-performance tires were double wrapped with circumferential belts. Where the belts overlapped, a splice was created. Now, those tires are spiral wrapped, using one continuous strand and leaving no splices behind.

Today, we look at tire issues we thought nothing of 20 years ago, and the result is a smoother riding, rounder tire.

In 2005, we look for the low spot on the wheel, measure the bead seats and place the tire sticker on the tire against the sticker on the wheel. Remember how we used to line up a tire sticker with the valve stem? With today’s stylized wheels, that no longer works.

In fact, a round tire with a reasonable force variation is the norm. Think of the tread of a tire as being supported by a series of “springs” radiating from the center of the wheel. As it rolls in contact with smooth pavement, each of these springs should deflect exactly the same amount as it travels through the tire footprint, resulting in no change in vertical tread movement – no vibration. At least that’s the idea.

But, we know that a weak spot in the tire, or weak ‘spring’ will deflect differently from the rest, and the strongest part of the tire will resist bending and remain stiff, causing vibration.

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Ride Complaint Culprits

In short, we still have a job to do when someone comes to us with a ride complaint. We still need to check for out-of-round tires, even if the chance of finding one is slim to none. If the tire is not out-of-round, check the wheel. An out-of-round wheel can also play a role in a ride complaint.

One vehicle maker has identified more than 100 different items that can contribute to a ride problem, and one Midwest tire dealer said it feels more like 1,000. Certainly, the new, lighter, quieter, more powerful cars of today are also more sensitive to ride complaints. Vehicle owners hear it and feel it in the cockpit and rush back to the tire dealer.

Your first job is to check the balance of the tire/wheel assembly. If the assembly is out of balance, remove the tire/wheel assembly from the balancing machine, and rotate it 90 degrees. Then, recheck the balance. Any corrective weight should be left where it is for now, but the new location is now 90 degrees away from its original location.

If the assembly is still out of balance, strip all weight and rebalance. If the vibration is still present, but excessive runout is observed, break down the tire/wheel assembly. Next, rotate the tire 180 degrees on the wheel, and remount it. Take care to ensure that the tire is uniformly mounted on the wheel, and be careful not to use too much lubricant.

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Other Considerations

Tires continue trending toward lower aspect ratios, and large-diameter wheels are more likely to be damaged by potholes, road debris and curbs. But, tires and wheels aren’t the only components that can cause vibration.

Lightweight suspension components don’t absorb road force variations easily. If a customer says the vibration happens on rough roads only, a suspension problem is a likely culprit. This is your cue to look beyond the tires and focus on broken or bent suspension parts.

Also, customers are holding onto their vehicles longer than ever. The average vehicle on the road today is roughly nine years old and has more than 100,000 miles on the odometer. These factors must be given some weight when looking for a vibration problem.

To determine what is actually causing the problem, ask your customer if the vibration feels more like a pulse or a buzz. Generally, pulses indicate balance or runout problems, while a buzz-like disturbance is normally associated with driveline or irregular tire wear issues. Vibration felt in the steering wheel is an indication that the problem is originating from the front of the vehicle. And, vibration felt in the seat indicates the problem is located at the rear. On the car, that is.

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If a ride disturbance suddenly occurs, check for mechanical problems, such as a bent wheel, a bent tire rod end or a lost balance weight. If the owner says the vibration has worsened over time, check for deteriorating mechanical or structural components. Installation of new wheels or recent vehicle repairs following an accident may point to vibration sources other than tires.

Put the vehicle up in the air, and check the driveshaft for irregularities. Also, check the exhaust system for any pipe that may be binding against the body or frame. And, out-of-balance brakes or rotors must not be overlooked.

All-Important Field Test

Consider driving the vehicle on the same road where the vibration was observed. Slowly accelerate through the speed range for a mile, if possible. For a smooth-road ride disturbance, accelerate and coast through the problem speed. You should be able to determine if the vibration is throttle or exhaust related.

If it occurs as a constant smooth road vibration, a single source is indicated. A disturbance at 45 mph to 50 mph that increases with speed indicates a balance problem. But vibration over a narrow speed range indicates other sources, such as high radial runout.

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Next, take the car out of gear, and coast through the speed range. As you reach the problem speed, press the accelerator, and match engine rpms as if the car were in gear. This will help determine if the vibration is engine related.

Continuing your search for the vibration, put the car in a lower gear, and again drive at the problem speed. Cycle the air conditioner on and off, and note any vibration. Also, note vibration that occurs as you apply/release the brakes.

Each of these checks helps determine whether the vibration is occurring in the driveline, the exhaust system, transmission, brakes or the tire/wheel assembly.

If none of this helps, replacing the tire or the wheel or both should be considered. Of course, this is a last resort. More often than not, you’ll resolve any problems before you reach this point.

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