Authored by: Tractor tyre expert | 30 September 2022
Your tyres have to bear your tractor’s load. Generally this means the weight of the tractor plus the weight of your implements, which represents a load that must be offset by the pressure in your tyres.
When you have an implement whose weight is transferred entirely to the rear axle of the tractor, it seems logical to compensate for this imbalance by adding additional weight to the tractor’s front lifting system to restore the correct overall balance.
However, what are the consequences if this ballasting is too much for your tyres, or for the recommended pressure? How can you be sure that you won’t damage your tyres as a result of the excess load? And how can you ensure that you don’t exceed the limits that your tyre technology can cope with?
A certain amount of mass is necessary in order to transmit power to the ground and obtain optimal tractive force, during tilling for example. Your machine’s traction capacity is effectively linked directly to its weight and ballasting is an efficient way of improving grip.
Nevertheless, when you are working with a rear implement, if you do not have enough ballast at the front, you should expect excess slip at the level of the front axle, as the lugs cannot fulfil their tractive role properly since they do not dig sufficiently deep into the ground, due to lack of weight.
The steering is less responsive and your front tyres will wear rapidly.
The loss of front axle motricity will be passed on to the rear axle and lead to excess slippage of the rear axle too.
The slip ratio can be considered too high when it is over 15%. This is easy to recognise by observing the footprint left by the tyres on the ground.
There is too much slip when the footprints are much wider than the normal thickness of the lugs.
Slip leads to loss of time and efficiency, extra fuel consumption and wear to the tyre lugs as well as damaging the soil.
If you need a lot of mass to counterbalance your implement, but your tyres are crushed by the load, it is possible to compensate for this by increasing the inflation pressure, although this option is not without consequences. When you overinflate your tyres this encourages slippage, especially when driving on loose soil (clay, wet soil).
The higher the inflation pressure, the further the tyre sinks into the ground, until it meets sufficient resistance to bear the load and provide traction.
Although agricultural tyres are designed to carry heavy loads, if your tyres are placed under too much strain, there may be irreversible deformation of the casing leading to internal breaks in the tyre. It is therefore essential to respect the load rating defined by the manufacturer if you wish to make your tyres last.
Each tyre has its own load index written on the sidewall, which fixes the maximum load that the tyre can carry at a given speed. This load includes the combined weight of the tractor, the implement and the ballast.
If your tyres don’t have a high enough load index to bear the weight of your implements plus the ballast necessary to balance out the combination vehicle, then you do not have the right tyre model.
You can keep the tyres but work with less heavy implements, or replace the tyres with IF technology tyres which allow you to increase the load by up to 20% more than standard tyre models.
Good ballasting doesn’t just consist in loading the front lifting system until the front axle is firmly driven into the ground. You need to spread out the mass properly between the front and rear axle, which will avoid premature wear to your tyres or even breaking the front deck.
To define the maximum amount of ballast possible, you must take account of the maximum load capacity of your tyres.
Then add ballast at the front in proportion to the weight of the implement, to obtain a load distribution (for 4WD tractors) of 40% at the front and 60% at the rear.
You must then weigh the axles with the implements, plus the ballast, to make sure you don’t exceed the tyres’ maximum load capacity.
Be careful, during work with certain implements that require heavy traction, the load transfer to the rear axle increases during traction. This changes the balance calculated beforehand when the vehicle is stationary.
You must take into account this load transfer by a slight increase in front ballast when stationary to compensate for the load during movement.
A good load distribution gives your vehicle better balance, which will lead to excellent driveability.
Ballasting is not only necessary to offset the weight of an implement. You must also consider the type of work to be done and the type of implement used.
The ballasting will not be the same if you use a drawn, mounted or semi-mounted implement, in the same way as if you are tilling or aerating the soil the ballasting will not be the same as for sewing or stubble ploughing.
Heavy ballast will be useful for deep tilling, to have more torque and of course transmit as much power as possible to the ground. With equipment such as the Maxi-Traction IF tyre, you will be able to increase the load without having to increase inflation pressure too much, as well as obtaining a larger soil footprint to optimise traction further.
Fendt 939 equipped with a 4 metre subsoiler with roller.
On the other hand, light ballasting at the front for front/rear balance will be perfect for stubble ploughing which does not require too much traction and for which the kilos of extra ballast would only represent a dead weight. But be careful about your working speed, which could cause slippage, because when working with light ballast you must respect the load/ pressure/ speed relation.
In certain cases ballast may of no use at all, such as for a tractor with a double-axle trailer on the road, in which case ballasting must be minimal to reduce fuel consumption.
There’s no point investing in a powerful tractor if it doesn’t have tyres that can cope with a very heavy load.
For optimal working conditions, you need to find the right balance between power, mass and agricultural tyre quality. There is a wide range of high-tech tyres available today that bear heavy loads while limiting inflation pressure.
If you are looking for a tyre that can carry heavy loads at low pressure to avoid compacting your land, Firestone’s Maxi Traction IF tyres will make an excellent choice. This top-of-the-range tyre, with its IF (Improved Flexion) technology, has a robust casing with resistant but supple sidewalls which allow for greater flexion and a load capacity of up to 20% more than a standard agricultural tyre.
Take the time to check or adapt your ballast and ensure that you have the right load distribution for the different operational configurations used with your tractor.
The right ballast together with a good tyre model at the right inflation pressure will be a source of savings at every level: less fuel consumption, less wear, and therefore less expenses.
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