Certain machinery are more likely subject to hopping problems than others such as agricultural tractors and graders. The causes are various and you’ll end up with a headache before you have identified the exact source! Over the years and as part of a R & D project, we have developed a systematic process that allows to determine the exact cause by elimination. That being said, up to now we’ve been unsuccessful to find guidelines from the major tire manufacturers. Therefore, it’s a personal approach. However, should you have any tricks, hints or experience you could share with us, we invite you to contact us. First, we will expose the possible causes; our diagnosis process will be the topic of our next article.
Causes related to mounting:
- One-piece wheel– « incorrectly seated bead »: whether ag, backhoe or OTR tires, one-piece wheels are being used more and more and they are a major challenge. The secret, use of lubricant. As a matter of a fact, not using a sufficient quantity of lubricant may not only be a risk to damage the beads but it would also prevent the bead to sit correctly on the wheel. Our experience at the factory showed that a 1/8’’ spacing between the bottom of the bead and the wheel flange will cause a flat spot on the tire of at least 3/8’’ and a bulge of 3/8’’ on the opposite side. Always talking by our experience, the operator will feel hopping but a visual inspection would not indicate anything wrong. Actually, it’s the most frequent cause when one-piece wheels are being used.
- One-piece wheel- « twisted tire »: When mounting tire(s), the use of a tire changer could cause torsion if an excessive force is applied and/or if an insufficient quantity of lubricant is used. As a matter of a fact, the bead will be properly installed on one side while on the other side the force of the mounting arm and rotation of the mounting equipment will lead to torsion. The tire structure will be misaligned which could lead to hopping. In addition, retreading won’t be possible for the deformed tire at the end of its useful life. Finally, only extreme cases can be diagnosed by a visual inspection.
Cause related to use :
- Overload and/or excessive speed: Just have a look at any major manufacturer’s data book to understand that there’s a limit to speed and loading capacity and that both are related: the greater the speed, the loading capacity is reduced. So, specifically in situation of add-ons to machinery such as: weigh-in, wider or expandable buckets, blower, additional blade it’s important to consider the overload. Even without add-ons, some machinery can exceed in speed the tires’ capacity. It’s a common case in the agricultural field, but also for backhoes or graders that are used at high speed during transit.
Causes related to tires:
- Diameter out of tolerance: The diameter of a tire is never perfect. However, the diameter must at least meet the tolerances recommended by manufacturers, which vary from machinery types to others. If the diameter does not meet tolerances on a driving front axle or between two axles, the power transmission system : differential gear or chain drive (graders)… will cause sliding of the defective tire(s) , which will lead to hopping and in worst cases, lead to transfer system’s failure. The variation of diameters may be caused at the time of manufacturing (manufacturer’s defect), by a wrong buffing process that does not comply with the diameter or simply by installing tires of different models or brands on the same machinery.
- Wrong size tires: Sometimes an identical wheel diameter but of different width is installed on the same wheel. For example, a 20.5R25 could be installed on a grader which would require 17.5R25. During assembly, an expert eye will notice something’s wrong but maybe not the operator. Not to mention a high risk of tire damages. Tire behavior could become unpredictable and it could also lead to hopping.
- Out of round: An out of round tire will lead to a flat spot or a bulge (generally on the opposite side) of more than 3/8’’ on 12’’ long will most likely lead to hopping. It could be caused by a manufacturing defect (new tire) or by a wrong buffing process (retreaded tire).
Causes related to the wheel :
- Wrong size wheels : Sometimes, one or more wheels need to be replaced. The replacement wheel will lead to an improper installation on the machinery, a wheel of incorrect width or simply different than the other wheels already installed on the machinery could lead to hopping.
- Damaged wheels or out of round: A tire could be deformed if installed on a wheel that has been either damaged or is defective. Therefore, this could lead to hopping. Hopping could be noticed only after a change of application. For example, hopping might not be felt at first on an ag tractor equipped with R1 tires which has one defective wheel (out of round) until winter tires are installed. Since they have a greater floor surface it’s only then that hopping will be noticed.
- Bad tightening: Of course, misinstallation of the wheel or nuts (studs) that have been improperly tightened will lead to different delicate problems and possibly to hopping.
Next article : Diagnosis process
Daniel Marleau – CEO LanOTR