We had the unique opportunity to be the first in the world to test out 2 sets of Trelleborg PneuTracs in the Netherlands and in Italy. The conclusion: the PneuTrac seems to offer unbeatable traction and remains stable regardless of the pressure. However: the accelerated development of modern, flexible tractor tyres could stand in the PneuTrac’s path.
Expectations are high for the PneuTrac: a tyre that converts from a ‘normal’ tyre into a track as the tyre pressure decreases. This innovation is of interest on plots where capacity, weight, moisture, soil compaction, and cost price are constantly in conflict. We were given the opportunity to test out a set of PneuTracs – an opportunity we seized with both hands.
After days of tests, analyses and comparisons, we concluded that the PneuTrac surprised us in 3 aspects: namely traction, stability, and comfort. As far as the footprint (and therefore ground pressure, weight per square centimetre) is concerned, the PneuTrac performs no better than a state-of-the-art radial tyre. We should mention here that the name PneuTrac illustrates the combination of tyre and track; this article will refer to the product name and ‘track tyre ’ interchangeably. In addition, PneuTrac track tyres are indicated by a ‘T’ (for track) instead of the usual ‘R’ (for radial), so we say 480/65 T28 rather than 480/65 R28.
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Traction can be measured most purely by measuring the tractive force between a pulling and a braking vehicle during motion. The independent Italian research institution CREA (Council for Agricultural Research and Economics) has a vehicle that can be used to perform such measurements. It tested the traction at various slippage percentages, using the PneuTrac (650/65 T38, and 480/65 T28 at the front) and comparable radial tyres – Trelleborg TM800s.
The measurements showed a 12 to 24% increase in traction using the track tyres – 17.6% on average. According to CREA researcher Maurizio Cutini, you could also regard this increase as a direct saving in terms of fuel and/or time. The greater the tractive force required, the greater the increase in traction. This means that the increase with PneuTrac will be even greater when ploughing, but barely discernible when mowing grass.
Say a tractor performs around 3,000 hours of pulling work over 10,000 operating hours with an average hourly consumption of 22 litres. The PneuTrac would save you a tidy 11,000 litres of fuel, a lot of money. Trelleborg also claims that the fuel saving was even greater in multiple tests, and this was endorsed by the winegrower we spoke to.
PneuTrac beats steel track
In Montespertoli, Tuscany (It), a New Holland T4.110N narrow track tractor has been running on a set of PneuTracs since April 2018. The challenge in the vineyard there is to have traction in the slippery clay, particularly when the subsoiler penetrates the soil or when a 1000 litre-capacity sprayer needs to be pulled up the slippery hill slope. “We have noticed more grip and more stability in particular, and especially when turning on a steep slope on the headland,” says driver Salvini Lorenzo. “With standard tyres, we sometimes had to leave those areas alone, but with the PneuTracs on, you can carry on for longer. They really make you feel safe.”
A demonstration of subsoiling between the rows of vines began with a tractor running on steel tracks. The 5.7 metric tonne-New Holland TK4050 had difficulty staying upright, and the tracks became caked with the heavy clay. When the driver steered to adjust, one track sometimes stayed completely still, which is another factor limiting traction.
Then the subsoiler moved to the conventional 4.1t narrow track tractor on PneuTracs. Three aspects struck us: firstly, the driver experiences far greater comfort and fewer jolts. Secondly, traction always remains intact, even when steering to adjust. And thirdly, the PneuTracs remain practically clean.
“In the past, it was impossible to do this work using conventional tyres,” says Mr Salvini. “We had to work with the steel tracks. But this is far more convenient. What’s more, you don’t need an additional tractor with a trailer to transport the tracked tractor. I get on site more quickly and the work is finished sooner.”
Mr Salvini’s boss also mentions the diesel saving, and of course that a tractor on PneuTracs is much cheaper to buy. On a full working day (4 sprayer tankfuls), the tractor on PneuTracs uses 29 litres of diesel, while another identical combination uses 40 litres. That equates to a saving of 33%. Mr Salvini puts it down to the fact that the PneuTracs have lower slippage.
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How can a PneuTrac provide greater traction while the footprint is barely larger? The only explanation that we could think of is that it always has an ultra-smooth and even footprint, regardless of the tyre pressure. No radial tyre can match that.
As the pressure decreases, the PneuTrac deflates into a track. You may think that its footprint is much larger than a standard tyre, but if we look at the footprint measurements of the small 480/65 T28, that is not the case, so it cannot be explained by lower ground pressure either. To begin with, the state-of-the-art radial tyre can flatten in 2 directions: lengthways and widthways. Yet there is a lower limit; if tyre pressure decreases too much, a radial tyre will run on its ‘shoulders’. A PneuTrac however does not flatten laterally, only longitudinally. It is not yet possible to say how this will turn out with larger track tyres in the future.
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In order to test the extent to which a PneuTrac is actually more comfortable, a tractor was fitted with track tyres first and then with comparable radial tyres. An extensive vibration test was also performed. The measurements show that the PneuTrac does not perform any better than a standard TM800 tyre.
Remarkably the test drivers rated them higher despite that. They experience a comfortable rocking effect, and the PneuTrac absorbs the greatest impacts. To do this, however, requires relatively low pressure of 0.6 bar or less. In spite of that low pressure, the PneuTrac remains extremely stable, and the tread stays in line with the trim.
Even so, something remarkable occurs in this vibration test. Comparing the test results of the PneuTrac and the radial tyre against previous vibration measurements with narrow track tractors, we see a significant difference. The state-of-the-art TM800 and PneuTrac tyres absorb vibrations upwards and downwards far more effectively than the smaller and firmer standard tyres of narrow track tractors. At high speed, vibration is reduced as much as 60%.
According to the vibration test team, this significant difference determines whether or not the driver suffers back problems in the longer term. This test shows that spending a little more money to ensure a good tyre not only benefits the soil, but also provides significant benefits for the driver’s comfort and health.
17% greater traction with PneuTrac tyres
What’s striking is that the difference in tractive force between conventional tyres (yellow line) and the PneuTrac (blue line) is greatest at between 20 and 30% slippage. On average over all of these measurements, the difference in tractive force of 17.6% is in favour of the PneuTrac.
According to the researchers of the CREA testing institute, you could directly convert that increase of 17.6% into a fuel saving and/or a time saving. One possible reason for the increase in traction is the PneuTrac’s smooth, flat contact surface with the ground, regardless of the tyre pressure.
The test was performed on stony soil that otherwise consisted of clay (6.4%) and sand (47.1%). The measurements were carried out by the independent research institute CREA. The test measurements were carried out during motion using an 8.2 metric tonne-John Deere 7530, while the braking vehicle was a Same Galaxy 170 carrying measuring equipment.
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The size of the air chamber in a standard tyre correlates directly with its load capacity. Which means that the higher the speed and the higher the load, the higher the air pressure needs to be. The air in the tyre determines both the horizontal (lateral) and vertical (longitudinal) stability, since the air exerts downward pressure on the tyre (from the trim outwards) while at the same time pressing the tyre into the edge of the trim.
These facts do not hold true for (mechanical) tracks, because they have no air chamber. A track undercarriage gains its stability from the structure of the undercarriage: the heavier and larger it is (such as supporting wheels, large drive wheels), the greater the load it can support.
And then there’s the PneuTrac, which does have an air chamber half the size of that found in a standard tyre. It’s air pressure only affects the vertical (longitudinal) stability, not the horizontal (lateral) stability. Just like a track, the PneuTrac gains its stability entirely from the structure in the sidewall. The hinged sidewall could therefore be considered a hybrid tyre, or indeed a hybrid track.
This is what posed the major challenge for the tyre manufacturer Trelleborg. The innovation lies in the tyre’s ‘hinge’: it must be stable, have a long service life, and provide as much stability as the mechanism in a track undercarriage. That’s why production began initially with the small 18 and 28-inch track tyres (2019), and quite some time later with the size 650/65 T38.
Head of Development Piero Manchinelli explains: “We intentionally started in the small segment with tyres that are sold to winegrowers. They require stable tyres that not only provide traction on inclines, but are also less likely to damage tree roots.”
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Looking back at all the tests and experiences with the PneuTrac, we were surprised about the high level of traction, and we know that the track tyre does not need to have a larger footprint or a higher level of comfort. What was still striking, though, was that the test drivers in Italy and during the testing in the Netherlands perceived a much higher level of comfort.
The PneuTrac is quite at home with low tyre pressure: that is where it excels. When pressure increases, the track tyre behaves in exactly the same way as a conventional tyre. That’s useful if you still have a few days of transporting work to do, but it’s not what the PneuTrac is intended for.
Trelleborg PneuTrac specs
Sizes: 280/70 T18, 480/65 T28 en 650/65 T38 (prototype)
Rim: fits standard rims
Weight: 280/70 T18: 70kg with rim. 480/65 T28: 230kg with rim
Availability: 18 and 28 inch limited available in 2019
Price: not known. Expected somewhere in between modern VF-tyre and tracs