AG Tire Talk: Common Out-of-Round Indicators

Questions: What are the indicators of an out-of-round problem and why is it important to have small amount of run-out when using today’s high-speed equipment?

Dave Paulk, manager, field technical services, BKT USA Inc.: Out-of-round tires can cause vibrations, road noise and uneven tread wear. With the bouncing and vibration, they can cause a rough ride. With the technology now used, many tires are more uniformly made than in days past. There are some things to check when vibrations occur that don’t necessarily have anything to do with the tire.

Tires and wheels are not made perfectly round. Each has a high spot and a low spot. If the high spot on a wheel is matched up to the high spot on a tire  - or low spot to low spot - this can cause a vibration. The high spot of one needs to be matched up with the low spot of the other. Match mounting the tire to the wheel generally ensures the best ride possible.

If a tire is not properly seated on the rim, this could cause radial or lateral vibration. The bead of the tire should be properly seated on the rim all the way around the rim to eliminate lateral run-out and swaying back and forth.

Low-horsepower tractors - less than 100 hp -  have a shorter wheelbase and can cause some vibration in the driver’s seat, which generally starts at about 20 mph. Sometimes this has can be caused by the wheel not being centered on the hub. Adjustable rims are common on smaller tractors. While these rims are great for adjusting the wheelbase width, they are bad for wheel run-out, which can cause vibration.

There are three ways to limit run-out on a tire. First, in production, when tires are made, there is a splice in the building process. Since it’s not possible to eliminate this, the effect on run-out can be reduced by manufacturing.

Second, matching the tire and rim together with high spots and low spots can minimize the amount of run-out on a tire and wheel assembly and reduce vibration.

Third, air pressures can be adjusted to ensure a good ride and minimal vibration based on the weight of the vehicle and the amount of weight carried. Over-inflation can play a big part in excess vibration at higher speeds.

Unless the tire is out-of-round from the start due to manufacturing, application can play a part in how the tire rides and rolls.

Oftentimes, the heavier the equipment, such as combines and large tractors, the longer the wheelbase. The slower the speed, the less vibration will be felt. The faster and lighter the machine, the greater the chance of feeling vibration at certain speeds.

There is equipment available to check for run-out on tires to determine it the runout exceeds the manufacturer’s recommendation. Radial and lateral run-out can be checked.

Radial run-out is the amount of up-and-down movement a tire shows. This is the most common cause of a problem and can cause a vibration in steering or the driver’s seat. The distance should be close to the same when measuring from the center of the wheel to the outside of the tread around the tire.

Lateral run-out is a side-to-side motion and is sometimes caused by not properly seating the tire to the rim.

No tire and wheel assembly is perfectly round, so there is always a bit of run-out. This should be minimized for the best tire and wheel performance. BKT has a tight tolerance for run-out and uniformity to minimize vibration problems caused only by tires. Match mounting tires to wheels and ensuring they are mounted properly solves many problems.

Greg Gilland, vice president, global agriculture, Maxam Tire North America: In general, out-of-round conditions on an agricultural tire stem from either poor quality control during manufacturing or poorly managed tolerance management in the tire specifications. In essence, an out-of-round tire is not round due to a distortion in the casing or tread that when mounted on a working platform can result in an unstable tire; increased vibrations; accelerated or uneven tire wear; and increased instability when mounted.

Ultimately, these results will reduce the tire’s expected service life. In extreme working conditions, out-of-round tires can also increase the friction of the tread, causing increased rolling resistance, uneven or abnormal wear and greater fuel consumption due to greater slip rates

Other possible causes that can lead to out-of-round conditions include poorly mounted tires that are not fully seated on the rims or flanges; poor storage practices, like barrel stacking or tires stacked too high, distorting the casing on the bottom tire of the stack; uneven storage or ground conditions, resulting in distorted or misshapen tires over time; tires that remain in one position for a long period of time without any movement or rotation, resulting in a distorted bead, casing, sidewall or tread area; poorly maintained or damaged wheels when the tires are mounted, which result in a out-of-round vibration or harmonics; poorly mounted tires on rims where the high spots are misaligned; and rims that are distorted from excessive use or poorly manufactured quality conditions.

Good housekeeping and best practices in the storage of tires can reduce the risk of tire distortions as described above. In addition, regular wheel inspections, replacement of damaged wheel components and wheel maintenance prior to tire mounting can also reduce the impact of an out of round tire.

In some instances, even new wheels may have issues like rim concentricity, which occurs when all the bolted wheel components are not round and resulting vibration harmonics when the tire is mounted. Therefore, the out-of-round conditions caused by a poor-quality rim or components may only be noticeable when operating on hard grounds or when roading from site to site. In those instances, adjusting the tires’ cold inflation air pressure can also help to mitigate or reduce the resulting vibration.

Most wheel and tire manufacturers minimize the risk of out-of-round by ensuring that tires and wheels are tested at their manufacturing facilities using run-out equipment. They will mount the tires on a rim and mark both the tire, as well as the rim’s high spot, to ensure alignment of the two spots, at this reduces the incidence of vibration.

Due to the nature of their field work or application, each agricultural platform will either have higher or lower incidence of vibration. Roaded tractors may only experience some vibrations when operating at speeds greater than 15 or 20 mph on hard surface road conditions.

High-clearance, self-propelled sprayers or floaters will inevitably experience a higher incidence of vibrations when you have an out-of- round issue either with a tire, the wheel or the mounted assembly. Harvesters may also only exhibit severe out-of-round issues or vibrations when moving from field to field on harder roads that can be masked at slower speeds - below 10 mph - when working in the field during harvest season. Below are some recommendations and suggestions to identify the root cause of the vibrations or out-of- round issues:

Evaluate the tire and wheel assembly lateral (side-to-side) run-out;

Evaluate the radial (up-and-down) run-out;

Use a run-out gauge to evaluate both the lateral and radial stability of both the tire and the wheel separately.

As the tire and wheel are connected as an assembly, it is imperative that both be examined together and then separately to ensure all the component variables are assessed. A high spot or heavier spot on a wheel or component like the inner disk can become further amplified on larger tires as the center of gravity is further removed from the spinning center. As a result, the vibration force becomes more amplified on the mounted tire contacting the working surface.

The continuing radialization of the ag tire industry has increased the need for tighter tolerances related to the tire and wheel assembly run-out.

David Graden, global account manager, agriculture, Michelin North America Inc.: In today’s agricultural landscape, especially with high-speed equipment like sprayers and MFWD tractors, ride quality issues are sometimes blamed on out-of-round tires. But in my experience working with Michelin Agriculture and supporting farmers and OEMs globally, it’s important to take a closer look at what’s really going on.

An out-of-round tire is one that doesn’t maintain a consistent radius as it rotates. This can be radial (up-and-down) or lateral (side-to- side.) On agricultural equipment, symptoms may include vibration at specific speeds; uneven wear patterns; reduced traction and soil contact; and operator discomfort and fatigue.

However, more often than not, the tire isn’t the issue. The issue is the wheel. Based on field experience and feedback from our technical engineers, it’s far more common for the wheel to be the source of an out-of-round condition.

Before assuming a tire is out-of-round, it’s critical to inspect for more common issues. These include improper mounting, bead damage and a bent or damaged wheel. These are far more likely to cause ride quality problems and/or out-of-round conditions and should be ruled out first. 

If a vibration issue does occur, it typically shows up during roading - not in the field. Soft ground conditions and torque tend to mask minor imbalances. On the road, especially at higher speeds, those imperfections become much more noticeable. This is especially true for MFWD machines, which have suspensions that can amplify vibration frequencies.

In contrast, 4×4 machines, with their heavier build and different vibration profiles, tend to absorb these issues more effectively. If both the wheel and tire roundness check out and the issue persists, it may be worth trying a different tire with a different lug count or tread design. Sometimes, the natural vibration frequencies of the machine simply don’t harmonize well with the tire’s pattern. Though rare, this mismatch can lead to noticeable ride disturbances, especially during transport at road speeds.

Ride quality matters, particularly as equipment becomes faster and more sophisticated. But when diagnosing vibration or imbalance, it’s essential to look beyond the tire.  

Chris Neidert, ag marketing, training and development manager for Trelleborg and Mitas tires, North America, Yokohama TWS: An out-of-round tire is not a perfect circle and known as tire radial run-out. There is another tire run-out: lateral run-out, which deals with the side-to-side wobble. We will discuss radial run-out.

There is no tire that is a perfect circle. Tire manufacturers strive to be as close as possible to a 100% round tire. The closer the tire is to a perfect circle (smaller manufacturing tolerances), the higher the tire quality. The higher the manufacturing tolerance, meaning larger out-of-round values, the higher the possibility for the wheel to cause an up-and-down hopping motion felt as vibrations when the wheel spins. Excessive radial run-out leads to a bumpy ride, irregular wear, and can cause vehicle vibrations. The higher the speed the equipment is moving, the more noticeable is an out-of-round tire or rim. Common causes of radial run-out include: 

Manufacturing. Believe it or not, tires are not perfectly round from the factory. The tighter the manufacturing tolerances the lower the out of round and higher the tire quality;

Improper mounting. A tire may not be seated correctly on the rim;

Wheels. Like the tire, some wheels are not perfectly round from the factory, resulting in an out-of-round wheel assembly scenario;

A bent wheel. This is often caused from an impact and can cause a tire to appear out-of-round.

Out-of-round may also be caused by improper or not match-mounting the tire and wheel assembly. High-quality tires and rims are tested before shipping and marked for their low spot and high spot.