The weight of your implement comes as an addition to the weight of the tractor and its ballast. But how do you know if the load transfer to the rear of the tractor is excessive?
What level of inflation do you need to compensate for this load correctly, but without too much pressure which would end up compacting my land?
If you decide simply to opt for average pressure, you haven’t answered any of these questions, which will nevertheless have major consequences both on tyre wear and on the quality of the work you do.
This is what you need to know about the load transfer to the rear axle of the tractor:
1. Know the tractor mass plus the weight of the implement
Unlike the front tyres, the rear tyres are really put to the test in the fields and on the road and are generally placed under considerable strain linked to the weight of the tractor and its implement.
An incorrect load distribution or an implement that is too heavy can lead to rapid wear to the rear axle and disturb the smooth running of your operations. That’s why it’s necessary to check the load and adjust the pressure settings to preserve your tyres every time you change implement.
You then have to distinguish between transport on the road and work in the fields with the implement engaged, because the load transfer will be quite different in both these situations.
As each tyre has a load index (supplied by the manufacturer) which must not be exceeded, you need to define the maximum load transfer that your rear axle can cope with to avoid damaging your tyres.
How do you weigh the rear axle?
The calculation of load is made with the implement raised to have the maximum level of load on the rear axle during transport by road.
Either you have the appropriate weighing equipment, or you can do the calculation manually if you know the weight of your implements and your tractor:
- M1 = Weight of the front ballast or front implement.
- M2 = Weight of the rear-mounted implement.
- d1 = Distance between the middle of the front ballast and the centre of the front axle.
- E = Distance between the middle of the front axle and the middle of the rear axle.
- d2 = Distance between the middle of the rear axle and the middle of the rear-mounted implement.
- Weight of the front axle = Manufacturer’s manual.
- Weight of the rear axle = Manufacturer’s manual.
EXAMPLE: FENDT 930 - 305hp - tractor equipped with a seeder
|Weight of the tractor
||Weight of the seeder (empty)
The load transfer of the seeder is 6,300 kg to the rear axle.
When you have clearly defined the load transfer you can establish the optimal working pressure.
In this precise example the optimal pressure in the fields will be 0.8 bar for the rear axle and 1 bar for the front axle.
This gives us a large soil footprint, so no compaction, despite the heavy weight of the combination vehicle and the significant load transfer to the rear axle.
Use front ballast to take pressure off the rear axle
Having made your load calculation, you can ballast the front of the tractor to take weight off the rear axle while respecting the maximum load capacity authorised for each tyre.
You must add mass in proportion to the weight of the implement to obtain a load distribution of 40% to the front and 60% to the rear. Ballast can take the form of metal weights or adding an implement to the front lift.
Balance the load transfer to the rear using front ballast
2. Adapt your pressure based on speed
Determining the load is not enough to define the best pressure setting, you must also bear in mind the expected speed of travel to avoid damaging your tyres prematurely.
Just like load, you should follow the maximum speed rating recommended by the manufacturer (indicated on the tyre’s sidewall).
If you go beyond this limit, the rubber in the tread of your tyre may deteriorate rapidly due to the overheating linked to speed. This may also provoke damage to the sidewalls and the internal structure of the tyre, obliging you to replace it prematurely and lose hundreds of hours of use.
If you don’t change the pressure, adapt your speed to carry more load
When you transport heavy loads by road, this often involves increasing the inflation pressure to compensate for the load.
If you choose to decrease pressure to avoid soil compaction in your fields and you drive fast on the road with underinflated tyres, they will wear very rapidly under the effect of the weight, with a risk of internal damage to the casing and therefore a complete deterioration of the tyre.
Reducing your speed significantly on the road helps reduce the alteration of the rubber linked to heating, because the tyre tread will be put under less pressure.
In any case, low speed makes it possible to compensate for the load without having to increase inflation pressure unduly.
A significant load transfer to the rear axle requires you to drive very slowly to avoid a compromise with average pressure which would be detrimental in terms of soil compaction.
EXAMPLE: IF 710/70 R42 - 179D tyre
|Pressure: 2,4 bar
Speed: 65 km/h
|Load capacity = 7,750 kg.
|Pressure: 2,4 bar
Speed: 10 km/h
|Load capacity = 9,840 kg i.e. 25% more.
|Pressure: 0.8 bar
Speed: 65 km/h
|Load capacity = 4,210 kg (speed not recommended with this level of pressure).
|Pressure: 0.8 bar
Speed: 10 km/h
|Load capacity = 5,345 kg i.e. 25% more.
GOOD TO KNOW:
Complying with the speed rating is important and helps preserve your tyre for longer based on a precise level of load. Nevertheless, if you exceed this limit there will not be any consequences to the structure of the tyre if you are not carrying a heavy load or if you have no load when driving on the road, on condition that you comply with road safety rules of course.
3. A central inflation system can compensate for the load on the rear axle
Central tyre inflation systems (CTIS) allow you to adjust pressure during use, without the driver having to get out of his cab.
It takes a few minutes to increase or reduce pressure depending on the load or the operations to be carried out.
Inflation systems are an interesting option to compensate for the load on the rear axle of your tractor when the implement is raised and you take to the road.
Without this pressure adjustment system, you would have to inflate or deflate your tyres manually using an additional compressor (which tractors rarely have) each time you change terrain.
A central tyre inflation system provides many other advantages.
The Sodijantes CTIS helps balance out pressure
Rapid pressure adjustments depending on the type of ground
Installing a CTIS for your agricultural tyres allows you to adjust pressure based on speed and type of ground.
- In the fields: if possible with the load and the implement lowered, you can drive at 10 km/h reducing inflation pressure to 0.8 bar to preserve your soil.
- On the road: depending on the load with the implement raised, you can drive at up to 50 km/h having increased the pressure to around 1.6 bar (to be adapted based on tyre dimension and load).
This allows you, for instance, to reduce rolling resistance, limit wear to the rubber and reduce your fuel consumption.
To avoid the compromise of opting for average pressure which reduces the quality of work and increases compaction in the fields, a CTIS allows you to adapt pressure constantly.
It will help you save time when you need to increase pressure before taking to the road, just by pressing on a button in the tractor cab.
Tank Air Wheels and complete CTIS
Rapid amortisation and reduction of tyre wear
Buying a CTIS is a useful investment which brings advantages right from the first year of purchase as well as an investment that is amortised rapidly (3 years).
According to manufacturer studies, this system allows you to reduce fuel consumption massively, to improve traction and limit soil compaction.
Your yields and overall productivity will benefit significantly.
Taking into account the load transfer to the rear tyres of your tractor allows you to balance out your combination vehicle better, to use the lowest possible pressure to avoid compacting the soil in your fields and to reduce slip, helping you save time on every campaign.
If you invest in a CTIS you will always have the right inflation pressure on the rear axle despite the significant load transfer when the implement is raised on the road. This reduces wear, increases the lifespan of your agricultural tyres, facilitates work and improves your vehicle’s traction.
To help you clearly define the causes of premature wear on your current tyres, we have developed a complete guide for you to download free of charge "How to detect abnormal wear in my tractor tyres"
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This information is intended only to make you aware of the technical and functional aspects of agricultural tires and their use. It does not allow you to make a judgment or a definitive conclusion on a given problem. Only your agricultural tire expert is able to make a technical assessment and take a final decision, case by case.