Nokian Tyres' Ari Törmä Highlights Why Correct Tyre Pressure is Crucial for Heavy Machinery

Ari Törmä, technical customer service manager at Nokian Tyres, stresses the importance of the correct tyre pressure in heavy machinery, according to a recent interview. Having spent seven years on the factory floor, followed by seven years in testing and R&D, and now monitoring tyres used by customers, Törmä has a comprehensive understanding of how tyres work and the common issues that arise.

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Nokian Tyres
Published on
May 2, 2023

One of the most critical factors Törmä emphasises is the importance of the correct tyre pressure. "The optimal tyre pressure plays an important role in getting the best out of heavy machinery," he says. Depending on the machine's work and the load, the weight of the work implements, and the speed, tyre pressure may need to be adjusted frequently during the working day. Heavy machinery often has many axles, with each one requiring its own optimal pressure in different situations, making it essential to keep a close eye on pressure levels.

Ari Törmä, technical customer service manager | Photo: Nokian Tyres

Nokian Heavy Tyres' technical manual provides a chart that outlines the ideal pressure, load-bearing capacity, and speed for each heavy tyre. As the speed increases, the same tyre pressure can carry less load, meaning that working on a field at slow speeds requires a much lower tyre pressure than high-speed road transit. When the tyre pressure is optimal according to the speed and load, the tyre is safe, has the best grip, does not warm up too much, and wears more evenly. Conversely, a single long road transport with incorrect tyre pressure can cause irreparable damage.

A Finnish farmer that uses Nokian Heavy Tyres sows crops very early in spring when the soil is vulnerable after winter. The farmer's sowing machine runs at just 5 km/h (3 mph) on the field, so the tyre pressure can be dropped as low as 0.4 bar (5.8 psi). The effect on the soil is drastically smaller compared to 0.8 bar (11.6 psi), which leaves much deeper tyre grooves on the soft field. The farmer is pleased that there is less soil compaction, and the fields remain fertile. There is an agreement not to drive any road transits with that pressure.

When operating a machine on an uneven terrain such as a forest, tyre pressure becomes an increasingly complex issue. A forestry forwarder, for example, may have the two rightmost tyres up in the air, leaving the two leftmost tyres to carry the entyre load momentarily. These load peaks can cause tyre sidewall flexing, leading to sidewall damage. Forestry contractors are often not aware of the correct tyre pressure under full load, with load peaks in the forest causing irreparable damage that is not covered by the tyre warranty. It is crucial to monitor tyre pressure regularly to get the best service life out of your tyre investment.

Regular tyre pressure monitoring is the key to extending the tyre's service life. A forwarder operator picking up timber left by a harvester may suddenly have a tyre losing pressure. Unfortunately, the operator cannot see or feel it happening until the track falls off the bogie. This can mean that a forestry tyre is damaged beyond repair, and the tyre must be replaced. When a tyre pressure monitor is in use, the machine operator has more options. They can unload the forwarder in time and drive home before the damage gets too severe, often getting away with just replacing the tube – a few hundred euros compared to a few thousand.

Tyre temperature is another variable to consider. As a rule, the tyre pressure should always be checked when the tyre is cold. The tyre temperature affects its pressure, which depends on the size of the tyre's airspace. A forestry tyre's pressure rises approximately 0.17 bar (2.4 psi) for every 10 degrees Celsius (50° F).

Only a few moments of working can lift the inner temperature of a harbor tyre from 0 to 80 degrees Celsius (32° to 176° F). This causes false results when checking the pressure – 10 bar (145 psi) appearing as 13 bar (188 psi).

In a Dutch terminal, the tyre handlers realised the importance of pressure monitoring. Originally, the pressure of their reach stacker tyres was monitored every Monday after the night shift, when the tyres were still warm. This gave too high results, and even the compressor would not fill them beyond 10 bar (145 psi). The maintenance manager changed their routine and started checking tyre pressures first thing Monday morning, when the tyres were properly cold. It turned out the tyre pressures were typically 8.5 bar (123 psi) instead of the recommended 10 bar (145 psi). This was enough to lower the tyre load-bearing capacity and service life in the long run. Just a simple change can make a big difference to the total cost of ownership of the machine.

Pressure equals stability

In container handling, excavating work, forestry work, backhoe loaders and many others, it is important to have a stable foundation for your work. Besides tyre structure, the correct tyre pressure plays a key role here as well. Only a tyre that has optimal operating pressure can absorb the shocks and maximise working accuracy.

It is the air that matters

“In conclusion, it always pays off to know what is going on inside your tyre. The airspace inside is the only thing carrying sometimes tens of tons of weight, so you should check and adjust the tyre pressure according to your work – at the right time, on regular intervals and when the tyre is cold. It will reward you with safer and more efficient working, lower tyre costs, lower fuel consumption, less unexpected downtime… and the list goes on.”


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