Authored by: Tractor tyre expert | 31 October 2021
Misalignment is one of the most frequent causes of mechanical wear to tractor tyres. Checking parallelism is a simple and rapid way of identifying a geometry problem which will save hours of use of your tractor tyres after minor adjustment.
When you discover irregular wear, the most common solution is to swap your tyres over to even out wear, but this does not fix the geometry problem and the tyres will continue to wear too fast. When an alignment adjustment is necessary, the sooner you do it the better to preserve your tyres and avoid having to replace them rapidly.
Parallelism corresponds to the left/right alignment of the front wheels relative to each other. Ideally, your tyres should be perfectly parallel to your tractor.
If the front of the tyres point slightly inwards, which is referred to as toe-in, there will be wear to the outside of the tyres.
Inversely, if the front of the tyres point outwards, which is referred to as toe-out, there will be wear to the inside of the tyres. In both cases an adjustment is necessary to reduce wear.
The two main alignment problems
It is necessary to check your tractor’s parallelism regularly. With the ruts, vibrations and travel over rough terrain that your tractor has to cope with on a day-to-day basis, toe-in or toe-out may occur and get worse progressively over time.
A progressive geometrical imbalance at the level of your agricultural tyres may come to light in different ways depending on your vehicle and your most frequent use of it.
Position the tractor without implements on a stable, flat surface such as a concrete floor or asphalt road. This is crucial to ensure the accuracy of the measurements to be taken.
Adjust tyre pressure to make sure that the wheels on each axle have exactly the same inflation pressure.
Measure the height between the ground and the middle of the wheel hub
At this height, make a mark with chalk on the edge of the rim at the level of the tyre bead.
Use a special measuring device for parallelism.
Block the device on the default setting, then perform an initial verification at the front of the tractor.
Place the measuring device between the wheels at the exact spot where you made the mark with the chalk.
Move the spike into position without unblocking the default setting and align the measuring device with this dimension.
Then position the measuring device on the rear wheels. If the device does not fit or if there is any discrepancy at the level of the spikes, you need to loosen the graduated measuring device spikes and adjust them so that they fit exactly from one rim to the other.
The variation obtained using this device represents the measurement of the parallelism.
For a two-wheel drive tractor, the acceptable tolerance is toe-in of between 0 and 3 mm.
For a four-wheel drive tractor, the acceptable tolerance is between 0 and -4 mm for toe-in and 0 and +4 mm for toe-out.
If you are not within these dimension, your tractor’s parallelism requires adjustment.
Certain manufacturers propose a much bigger tolerance, which would be detrimental to the durability of your tyres which already face a huge amount of strain in terms of wear, with slippage for example or the abrasiveness of the ground, etc.
Our verification showed a difference of 7 mm, requiring an adjustment of the parallelism.
If you notice a problem with your tractor’s parallelism, take a quick trip to your usual tyre dealer who has the right equipment (professionals have laser control systems) to make a precise adjustment to the steering ball joints and obtain optimal alignment of your vehicle’s wheels.
Due to the mechanical strain exerted when four-wheel drive is engaged during work in the fields, it is advisable to opt for toe-out of 1 to 1,5 mm, because over time, the external strain placed on the tyres tends to increase toe-in progressively at the level of the front axle.
Regular, systematic verification of your parallelism is a good way of saving thousands of hours of use of your front set of tyres and avoiding having to replace them.
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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