Tractor power is not the only decisive criterion for optimal productivity. Although it is perfectly logical to give priority to power (in accordance with the size and weight of the implements used), there is another key factor that must be taken into account in order to get the most power from your tractor. This factor is often underestimated: it concerns the dimensions of the tyres or whether they are suitable for the work to be done and the actual weight of the implements drawn.
It is the tyres that transmit engine power to the ground. If they are not suitable or they are undersized, the tractor’s power cannot be harnessed to the full. This is why it’s vital to get the tyre dimensions right when you replace your tyres, especially if you decide to work with bigger, heavier implements.
To maximise performance, it is important to make the right choice of tyres. The wrong choice may lead to loss of traction, accelerated tyre wear and an overall reduction of productivity.
In this article we look at what you need to know about trye dimensions.
1. What is the importance of agricultural tyre dimensions for optimising productivity?
Each agricultural tyre model is designed for a specific use. Working with tyres that are unsuitable or too small can lead to many inconveniences.
If your tyres are too small for your implements or their load, the risk of slippage will increase, especially in wet conditions or on loose soil.
Tyres that are not the right size will have a smaller contact patch with the ground. They won’t have a large enough bearing surface for the weight of your implements, obliging you to increase inflation pressure to compensate for load.
Rolling resistance will increase and the tyre will sink deeper into the ground, damaging the soil as well as causing slip.
Bear in mind that excess slip slows down your work rate and increases your fuel consumption, making you lose both time and money.
2. Is your tyre series adapted to your implements?
The problem with the sizing of your agricultural tyres may be linked to use of a tyre series that is too small, preventing you from adapting to the weight of your implements.
In this case, you will not get the most from your tractor.
In short, you will not be able to increase its load capacity since you will have to respect the load index recommended by the manufacturer in order to avoid damaging your tyres prematurely.
Your machine’s traction capacity will be too weak. This will lead to extra fuel consumption and a considerable loss of time.
Fitting a bigger tyre series when you replace your tyres will provide a simple solution to excess load and soil compaction. This is therefore the best alternative to the problem of undersizing.
The load is given for a speed of 30 km/h with an inflation pressure of 1.3 bar.
Except for the 300/95/R52 tyre at 1.6 bar at minimal pressure authorised for this model
By choosing a wider tyre series, you obtain a greater volume of air in your tyres without changing the rolling circumference linked to the drive ratio.
You can increase your tractor’s load capacity, which will allow you to work with heavier, wider implements to boost your productivity.
Wide tyres improve your machine’s traction capacity while working at lower pressure to preserve the soil in your fields.
Widen the rims with a smaller diameter to gain load capacity
Without changing the height of your tyres to have the same wheel passage, you can choose wider rims by reducing their diameter.
The volume of air will be much greater as well as the load capacity.
Here are a few examples of wheels with the same height but a load capacity of 30% more by changing the diameter and width of the rim in addition to the tyre:
- 42’ rim - 580/70 R42 tyre: load = 4,235 kg
- 38’ rim - 710/70 R38 tyre: load = 5,325 kg
- 32’ rim - 900/60 R32 tyre;: load = 5,515 kg
30% more load capacity by changing the tyres
and the rims (for a speed of 30 km/h at 1.3 bar)
UA tyre and rim size that is better suited to your implements increases the load capacity and allows you to use your tractor’s power to the full.
Your traction improves because the soil footprint is much bigger and the tyres have a better grip on the ground.
3. Problems with braking linked to tyre size
Tyres are particularly important for the tractor’s braking system.
Tyres with the right dimensions maximise adherence and transmit braking power to the ground better.
The brake force depends on the coefficient of adherence of the tyre to the ground and the total mass of the agricultural combination vehicle.
Appropriate tyre size is essential when braking
Tyre dimensions can therefore have an impact on braking, especially if the tyres are undersized compared to your trailer’s load. For example a 150hp tractor with a total loaded weight of 40 tonnes with its trailer represents an unsuitable load/power/braking ratio.
As the size of the tyres is generally consistent with the tractor power, if your trailer is carrying too much load, your tyres are unlikely to be the right size for this load.
Excess load transfer during braking
Will your tyres cope with the load transfer during braking?
During emergency braking, the brake force will be felt directly at the level of the tyre. The distribution of forces on each wheel is not the same.
The front wheels bear most of the strain and the transfer of dynamic load to the front axle may destabilise the combination vehicle.
The risk increases if the global mass is too high, if your trailer has to brake while cornering or going round a roundabout.
When the contact patch with the ground is too small, the tyres are unsuited and the braking distance will be increased by several meters before coming to a complete stop.
There are several factors which have an impact on tyre behaviour in emergency braking situations, including:
- Trailer mass
- The strength of the braking system
- The tyre contact patch with the ground
- The adherence of the tyres
- The stability of the tyre faced with an increase in dynamic load
- The casing’s resistance to load.
It is therefore essential to have the right tyre dimensions to ensure optimal adherence to the ground and a reduced emergency braking distance.
4. The Maxi traction tyre: ideal for adapting your tyres to your equipment
Agricultural tyre manufacturers are aware of the problems linked to the different size constraints associated with tyres.
They are constantly developing innovative, high-tech tyres to adapt to the type of ground, weather conditions and above all load management.
At Firestone, the Maxi Traction range offers a wide selection of tyre dimensions to cover all load and power options.
Designed using ultra-resistance and lasting components, this radial tyre has a robust casing with a reinforced structure which allows it to carry up to 30% more load than a standard tyre.
It is perfectly balanced and provides optimal stability in the fields and on the road, even in extreme conditions.
Firestone Maxi Traction 710/70R38 tyre
A wide range of dimensions with many advantages
Firestone’s Maxi Traction tyre range helps to improve your productivity and reduce your operating costs:
Thanks to its supple, resistant sidewalls, the Maxi Traction tyre allows you to work at an inflation pressure of between 0.8 and 1.6 bar.
Time savings in the fields
Its Dual Angle lugs provide better traction.
Reduced wear on the road
The Maxi Traction tread is designed using anti-wear components to resist abrasion on the road. Its reinforced casing allows it to carry a heavier load than a classical tyre.
Slip is reduced in the fields, which results in significant fuel savings.
Safety and driving comfort
The width of the tread and its overlapping lugs offer a smoother driving experience with greater shock absorption and excellent road handling capacities, even when loaded.
It is crucial to understand the importance of having the agricultural tyre dimensions that are best suited to your use, your tractor’s power and the weight of your implements.
Undersized tyres can lead to:
- a risk of the tyre coming off the rim,
- an increase in slip,
- more rolling resistance,
- extra fuel consumption,
- soil damage.
By choosing tyres with a high volume of air and wider rims with an appropriate diameter, you can:
- increase your load capacity,
- ensure optimal adherence to the ground,
- reduce your emergency braking distance,
- guarantee optimal, efficient use of your machine.
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.