Certain machinery are more likely to be subject to hopping problems than others, such as: agricultural tractors and graders. Last month, we outlined the possible causes… Today, we’d like to share our method to find the cause by elimination. Keep in mind that the tire is rarely the source of the problem… Our eyes can mislead us!
Step 1: Road Test
A road test must be performed with the operator to really feel the hopping and particularly to note the speed when hopping begins to be felt. If the problem is felt at low speed, it’s normally a problem related to a combination of wheel/tire/mechanics. If it’s in between two speeds, it’s possible that the combination go into resonance at a precise vibration. And if the problem is felt at high speed, the tires installed are probably inadequate for the application.
***Most operators will tend to say that hopping is the result of a misalignment. It never reflects reality… Do not forget that unlike car tires, their rotation is 5 time slower due to their great size and slow speed of the machinery. … A balancing problem… Never in a hundred years!
Step 2: Check list
- What is the speed rating of the tires in comparison with the speed reached?
- What’s the load capacity of the tires in comparison with what’s requested…? Be very careful to modified machinery that are often heavier than originally.
- What is the tire pressure? Is it as prescribed by manufacturer’s recommendations? Make sure to validate with manufacturer’s Data book.
- Are wheel dimensions appropriate for all the tires? Be careful to wheel changes… It’s wrong to say that a 25’’ tire will fit on every 25’’ wheels! I recommend the use of manufacturer’s databooks to validate the appropriate wheel size.
- Are the nuts securely tightened?
Even at this stage, you can easily figure out the possible causes by yourself without a service unit call… Tires that exceed their speed capacities and/or load capacities will get a reduced life expectancy and in addition will behave in an erratic manner. Adjust pressures as recommended by manufacturer and repeat road test.
With the assistance of a service unit
Using a flexible measuring tape, measure circumference of each tire. Then, compare difference in height. For severe tolerances, generally consider 1.5% but it can go up to 5%. For further details, please read machinery manufacturer’s guide. NERVER USE A STANDARD MEASURING TAPE TO MEASURE DIAMETER FROM GROUND LEVEL!!!
Lift machinery, and one tire at a time, use a defined point, ideally a wooden block. Place it as close as possible to the tire. The use of a laser or any other sophisticated tool is not required for a tire of this size! You might also use a chalk at the highest point.
That way, while rotating the tire slowly, you’ll either see a chalk mark or not. Any deformation smaller than 3/8’’ on more than 10’’ found on the sidewall and on the wheel should be marked. In hopping situation, there’s generally a flat spot on one side of the tire and a bulge on the opposite side. If a deformation is noticed, mark it on the wheel as well.
Remove the tire and repeat the wooden block test but this time, only with the wheel. You will then be in a position to determine if the problem comes from the wheel or the axle.
Mount tire using the proper lubricant while rotating at 90⁰. Repeat block test. If tire still shows deformations at marked spots, the tire is the source of the problem. However if the tire’s shape is back to normal, mounting is the cause. If tire shows deformation (s) in other areas, the wheel is the source of the problem.
Should you have any questions or comments, please do not hesitate to contact us!
Daniel Marleau – CEO LanOTR