Authored by: Tractor tyre expert | 31 August 2022
Instability and tractor vibrations when driving accompanied by a lateral swaying motion from right to left may be the sign of a tyre with a manufacturing defect. This is known as run-out or out-of-roundness and corresponds to a slightly oval tyre shape.
However, there are numerous causes linked to tyres that can produce this type of vibration and to ensure that you are in the presence of a tyre that is misshapen as a result of the manufacturing process, you will need to have the concentricity of the tyres verified by a professional with the right equipment, once you have checked the following points:
There are multiple possible causes of vibration in agricultural machinery, many of which are linked to the tyres.
The slight vibration due to the form of the lugs which regularly come into contact with the ground is relatively normal. However, if these vibrations increase and can be clearly felt in the tractor cab, this is more problematic and can lead to a major problem linked to the tyres, causing accelerated wear and reducing the tyres’ lifespan.
When you start up your tractor, all the parts involved in transmission (the drive chain) begin to vibrate normally in tune with the engine. The same goes for your tyres when you drive, with the vibrations linked to the rhythm of lug contact with the ground.
When these two sets of vibrations have the exact same rhythm, they can generate resonance and are likely to produce an oscillation frequency that will amplify the vibration.
To ensure the problem really comes from your tyres, you just have to compare the level of vibration when driving to vibration while stationary with the engine running.
Good to know:
You can correct this problem by reducing or increasing the pressure in the tyres to change the shape and modify the frequency of vibration caused by the tyre’s contact with the ground.
If this doesn’t work, it’s worth changing tyre series when you replace your tyres to alter the size and therefore the vibration frequency.
Certain types of rim may have a slightly oval form, especially those whose disc is welded to the base, which leads to vibration when driving. You therefore need to check that the vibration is not coming from the rim.
Your tyre dealer has the right tools to establish the rim’s high points and low points. If the measurements taken are outside acceptable standards, the tyre deformation is certainly due to a manufacturing defect, obliging you to replace the wheel.
Good to know:
If the rim is made up of several parts, with a disc bolted to the crown, you should check that the connections between the rim and the disc are properly centred. If there is any irregularity, loosen the bolts and readjust the alignment.
A mounting error may result in some extent of vibration. When you mount your tractor tyres, you must ensure that they fit the rims perfectly.
Whether the tyres are mounted manually or mechanically, lubrication is important, because a poorly lubricated bead may not fall into position correctly on the edge of the rim. This incorrect positioning generates vibrations when driving (with a possible loss of air) accompanied by lateral swaying.
Good to know:
You can solve this problem by removing the beads from the rim and remounting the tyre once you have lubricated the beads again properly. When you remove the bead, check that it is not cut, damaged or seriously misshapen, which would oblige you to replace the tyre.
Incorrect geometry can cause vibrations which increase with acceleration. There are two main geometry problems possible:
Good to know:
Wheel alignment should be checked regularly, bearing in mind that your agricultural tyres are permanently under considerable strain, which can alter their settings.
Having carried out the above check-ups and verifications, if the cause of the vibration has not been established, it’s probably a problem of wheel run-out linked to the manufacturing process.
A new tyre is never totally 100% round, but may be slightly oval, with an acceptable tolerance margin of 2 mm, which has no consequence on its use.
Your tyre dealer has measurement tools to determine whether your tyre is compliant. The tool used will check that the centre of the rim or the wheel is exactly at the same spot as the centre of the tyre.
During measurement, the radius to the wheel axis centreline must be same everywhere. If there is a difference of more than 5 mm, the impulsion linked to this out-of-roundness will be felt in the tractor cab each time the wheel rotates and will cause a vibration that increases with speed.
If the tyre is too distorted, you will have to replace it.
There are certain cases in which out-of-roundness can either be compensated or corrected, depending obviously on the extent of the run-out which must remain very close to the tolerance threshold of 2 mm.
Certain discount rims may also have slightly oval shapes. If the tyre and the rim are oval shaped, you can use tyre/rim measurements to rotate the wheel one half-turn on the rim.
This operation will have a recentering effect, with the tyre compensating for the deformation of the rim and vice versa.
In certain cases where the oval form is not too pronounced, on a new tyre for example, returning the tyre to the factory will enable the defect to be corrected using a specific tyre uniformity measurement and correction system. This device will measure the extent of the tyre deformation and restore its uniformity using an integrated grinder.
In appearance, all agricultural tyres look the same: same colour, similar lug pattern… but they are not all worth the same in terms of quality. In discount tyres, the materials that are less resistant to deformation or strain may result in a large amount of tyre run-out which is difficult to detect prior to mounting and driving.
On the other hand, top quality tyres are made to last: more natural rubber, quality fabric layers, higher number of plies, improved resistance, etc. For example, FIRESTONE’s agricultural tyres are the fruit of substantial R&D investment, several years’ of experience and a rigorous selection of high quality materials. Before being placed on the market, they systematically undergo very thorough testing and control procedures to guarantee their quality. Laser checks are used to identify any manufacturing defects.
Unlike discount tyres, all FIRESTONE agricultural tyres are subject to additional human testing to ensure that they are top quality. Specialist workers carry out scrupulous testing to detect the slightest minor defect, such as out-of-roundness or any other irregularity.
Once the tests have been completed, FIRESTONE offers a warranty of up to 10 years in the event of any manufacturing problem.
With Firestone, you have the guarantee of tractor tyres that deliver a real advantage, and that in choosing our brand, you can work worry-free.
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