Can your harvester tyres be used on the tractor?

Your combine-harvester only comes out a few weeks at a time, then is put aside for the rest of the year.
During this period, its agricultural tyres, which are often relatively new and in very good condition, are unused. Which brings up an interesting idea: why not fit these harvester tyres on your tractor which is used all year round? After all, it could prevent you from having to buy an extra set of tyres and therefore lead to immediate savings.
The logic seems quite compelling: making the most of equipment that has already been paid for, avoiding premature ageing of tyres which spend most of their life unused.
But behind this simple idea lies a substantial question: are harvester tyres and tractor tyres really interchangeable? Do they have the same technical characteristics, the same resistance, the same efficiency in the fields?

At first glance it seems feasible if the dimensions are similar. Yet each type of tyre is designed to meet specific requirements. And if certain configurations seem possible, others could endanger your performance, your soil… and the tyres themselves. So is it an easy way to save money or a false trail?

In this article, we analyse in detail the differences between harvester and tractor tyres, their potential compatibilities and the situations in which swapping them over could – or not- be envisaged.

1. Why use harvester tyres on a tractor?

Recuperating the front tyres of a harvester that is not in use to fit on a tractor is a legitimate temptation. However, this practice is not always appropriate for various reasons.

Why is it a miscalculation?

The main reason is the difference in design. A harvester tyre is effectively designed to carry extremely heavy loads, such as the weight of the harvester with its full hopper.

Its technology, in the case of IF or VF CFO (Cyclic Field Operations) tyres, allows it to carry up to 86% more load on a cyclic basis as the hopper fills up, without changing the inflation pressure.

Moreover, these tyres are not made to cope with the torque and continuous tractive force of a tractor. Engine torque, which is the force necessary to bring into motion an implement that is hindered by its attachment to the ground, puts the tyre sidewalls and casing under intense pressure.

A harvester tyre is not built to withstand this type of strain. This leads to premature wear, difficulties with motricity and, in the worst cases, to a breakdown (tear, burst tyre) which can cause considerable damage and immobilise your vehicle.

2. Tractor tyres can work on a harvester but there are few compatible dimensions

Inversely, the idea of equipping a harvester with tractor tyres could seem feasible, since both machines have similar sized tyres.

Here again, certain elements must be taken into account before opting for this solution.

Problem with dimensions

Although tractor tyre dimensions can technically adapt to a harvester, the compatibility is limited.

And for good reason; the most load-resistant tractor tyres are often too bulky to adapt to combine-harvesters.

This can cause problems with the space required for the vehicle body or other machine parts. And this limitation considerably reduces the available options, making the choice of the right tyre size difficult and often approximate.

Insufficient load capacity

The main problem lies in the load capacity. Even the most high-tech tractor tyres, such as IF (Improved Flexion) or VF (Very High Flexion) tyres, are not designed to cope with the extreme cyclic loads of a harvester.

A harvester can reach a weight of more than 37 tonnes once the hopper is full, with this load fluctuating permanently during the harvest.

Smaller sized tractor tyres are therefore not sturdy enough to handle these weight variations, which leads to premature wear and a higher risk of breakdown.

3. In which situation is it possible to swap over harvester tyres?

The use of harvester tyres on your tractor can be envisaged, but many precautions must be taken (however this practice is not recommended).

These are the very few instances when it is possible

The interchangeability of tyres between a harvester and a tractor is possible in very specific situations. This is the case in particular for work requiring very little torque. For example light soil preparation work, sowing or haymaking.

These activities with no torque are not intensely demanding in terms of engine power or the tractor’s transmission system, which reduces the risk of damaging the tyres.

However, you must bear in mind that this interchangeability is out of the question for heavy work such as:

• tilling,
• decompaction,
• or any other activity requiring a lot of traction with continuous torque.
• ou toute autre activité nécessitant une traction importante avec du couple en continue.

This type of work places considerable strain on the tyre casing and sidewalls, and harvester tyres are not designed for this.

The design of the casing is very different for each model. The plies are not assembled the same way for tractor tyres, which have to deal with intense torque during the horizontal traction of implements while maintaining good stability, and harvester tyres which are designed to withstand a considerable vertical load linked to the weight carried.

The technical limits of this change of tyres

Even in the limited cases where the tyre swap is possible, the technical limitations are multiple.

• For a start, a harvester tyre is not designed to work at a very low inflation pressure, which is not ideal for protecting the structure of your soil. In short, the structure and casing of these tyres is optimised to carry very heavy loads and not to flex and flatten out on the ground at low pressure like tractor tyres.
• In addition, motricity will be reduced considerably. Why? Because the design of the harvester tyre casing has not been studied to transmit the tractor’s engine power efficiently. The tractive effort will be less effective, leading to a high slip ratio, rapid wear and extra fuel consumption.

4. Each tyre has a specific use

Choosing the right tyre is essential if you want to optimise the efficiency and profitability of your farm. Don’t forget that each type of tyre is designed for specific tasks and machines.

Investing in tyres that are adapted to each use is therefore the best way to optimise your equipment’s performance and useful life.

Tractor tyres (e.g. VF VT-TRACTOR)

VF technology tractor tyres, such as Bridgestone’s VT-TRACTOR tyre, are working tools that are engineered to optimise traction and soil preservation.

They result in a very good work rate and offer many benefits:

• The casing is developed to withstand a lot of torque with an innovative lug design. The “Involute” lugs ensure maximum transmission of power to the ground with efficient self-cleaning, thus reducing slip.

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• Working at a very low inflation pressure: these high-tech tyres are built to operate at an extremely low inflation pressure, from 0.6 to 0.8 bar. This flexibility makes it possible to expand the tyre’s soil footprint, which minimises compaction, thus protecting the soil structure.

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• They can handle 40% more load than standard tractor tyres, but this is not sufficient to be able to cope with the load of the harvester, above all the cyclic loads during the harvest.

Harvester tyres (e.g. VT-COMBINE)

Unlike tractor tyres, harvester tyres such as the VT-COMBINE tyre are optimised for their load capacity.

Their characteristics are designed to withstand the extreme and variable weight of a combine-harvester:

• Very high load capacity: thanks to IF/VF CFO (Cyclic Field Operations) technology, these top quality tyres can carry up to 86% more load than a standard tyre, even at a lower inflation pressure.

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• Resistance to cyclic variations: their reinforced casing is specially designed to manage fluctuating loads caused by the filling up and emptying of the hopper.

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• Robust design: features such as the S-Line bead secure the connection between the tyre and the rim, ensuring excellent stability and avoiding the tyre coming off the rim, even when working on sloping land or rough terrain.

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• They can bear a very high weight-related vertical load, but are not designed to handle a lot of torque because the harvester doesn’t have to pull an implement that is slowed down by the ground.

The Bridgestone-agriculture.eu blog is written and administered by tractor tyre experts who are available to provide you with the advice you need on the subject of your agricultural tyres. They allow you to maximise your productivity with information on all subjects linked to tyres: Technical data for agricultural tyres – Agricultural tyre performance – Air pressure advice, Solutions to avoid soil compaction – Sprayer tyre pressure – Why and how to ballast your tractor tyres – etc.

To take it one step further and increase the profitability of your farm, the blog Bridgestone-agriculture.eu provide a free, highly detailed eBook which explains the essential role of the agricultural tyre in your productivity.

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