Wed April 26 10:30 am 2023 in category Articles
Why is the tire pressure on heavy machinery so important?
I often describe my carrier path in the tire industry as seven years making tires on the factory floor, the next seven years breaking tires in testing and R&D, and now checking tires that are used by our customers. This full circle has taught me a lot about how the tires work structurally and what typically gives in. I hope I can use the accumulated knowledge to benefit both the tire manufacturer as well as the end user. One of the most crucial things I want to talk about is the importance of the correct tire pressure.
Here up north, most car owners have two sets of tires: one for winter and the other one for summer. Changing tires twice a year raises the general awareness about the significance of monitoring the tire pressure, as it becomes clear that spending six months in storage tends to cause some air to leak out. So, no “set up and forget” here.
The optimal tire pressure plays an important role in getting the best out of heavy machinery. For the same machine to perform at its best, you may need to adjust the tire pressures many times during the working day, depending on the work at hand, the weight of the work implements, the machine load and speed – just to give some examples. And of course, unlike cars, heavy machinery often has many axles and a weight distribution far from an even 50/50. Each axle has its own optimal pressure in different situations.
The trio of speed, pressure and load
Nokian Heavy Tyres technical manual includes a chart for speed, pressure and load-bearing capacity for each heavy tire. It shows that as the speed increases, the same tire pressure carries less load. So, as a very practical example, working on the field at slow speeds calls for much lower tire pressure than doing a high-speed road transit. When the tire pressure is set optimally according to the speed and load, the tire is safe, has the best grip, it does not warm up too much and it wears more evenly. On the other hand, just a single long road transport with a wrong tire pressure can cause irreparable damage.
One of our customers, a Finnish farmer, sows their crops very early in spring when the soil is vulnerable after winter. Their sowing machine runs at just 5 km/h (3 mph) on the field, so the tire pressure could be dropped as low as 0.4 bar (5.8 psi). It is surprising how the effect to the soil is drastically smaller when compared to 0.8 bar (11.6 psi), which leaves much deeper tire grooves to the soft field. The farmer is very pleased that there is less soil compaction, and the fields remain fertile. We also made an agreement not to drive ANY road transits with that pressure!
Off road is a different game
When the machine is operated in an uneven terrain such as forest, the tire pressure becomes an increasingly complex issue. Take a forestry forwarder for an example: on a level surface it is easy to define the optimal tire pressure for each axle according to the evenly distributed load, but on the highly uneven forest floor the two rightmost tires can be up in the air, leaving the two leftmost tires to carry the entire load momentarily. These load peaks can leave just one tire to carry tens of tons of timber. As the tire pressure is the only thing carrying the weight in the tire-wheel combination, the forestry tires should be filled to their maximal operating pressure.
In my work, I often witness forestry machine contractors are not aware of the correct tire pressure under full load. The load peaks in the forest lead to the tire sidewall flexing too much, causing sidewall damage. If the tire pressure is, say, half of the maximal operating pressure, the damage is considered accidental and is not covered by the tire warranty.
The importance of pressure monitoring
Regular tire pressure monitoring is the key when you want to get the best service life out of your tire investment. It is often the case that a forwarder operator is picking up the timber left by a harvester, and suddenly one tire starts to lose pressure. Unfortunately, the operator cannot see it happening or feel it in any way until the track falls off from the bogie. This can mean that a forestry tire is damaged beyond repair. And what’s more, you still need to limp home from the forest. After that, nine out of ten times the tire must be replaced.
When a tire 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. In that case, they often get away with just replacing the tube – a few hundred euros compared to a few thousand. The outer tire will live on and last for its intended service life.
Checking the pressure in right temperature
Besides load, speed and operating surface, there is yet another variable: the tire temperature. As a rule, the tire pressure should always be checked when the tire is cold. This applies to cars as well as to heavy equipment. How the tire temperature affects its pressure depends on the size of the tire’s airspace. In a forestry tire, the pressure rises approximately 0.17 bar (2.4 psi) for every 10 degrees Celsius (50° F). In harbor tires, the pressure rises about 0.35 bar (5 psi). Only a few moments of working can lift the inner temperature of a harbor tire 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 tire handlers realized the importance of pressure monitoring. Originally, the pressure of their reach stacker tires was monitored every Monday after the night shift, when the tires 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 tire pressures first thing Monday morning, when the tires were properly cold. It turned out the tire pressures were typically 8.5 bar (123 psi) instead of the recommended 10 bar (145 psi). This was enough to lower the tire 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 tire structure, the correct tire pressure plays a key role here as well. Only a tire that has optimal operating pressure can absorb the shocks and maximize working accuracy.
It is the air that matters
In conclusion, it always pays off to know what is going on inside your tire. The airspace inside is the only thing carrying sometimes tens of tons of weight, so you should check and adjust the tire pressure according to your work – at the right time, on regular intervals and when the tire is cold. It will reward you with safer and more efficient working, lower tire costs, lower fuel consumption, less unexpected downtime… and the list goes on.
Ari Törmä, 28 years of tire experience at Nokian Tyres
Technical Customer Service Manager
Questions about tire pressure?
Contact: [email protected]
With smart pressure and temperature monitoring from Nokian Tyres IntuituTM smart tires and mobile app, you will always know how your tires are doing.
Our technical tire manual is your tool for finding the right tire for your work. In addition to tire and supplementary item information, this manual focuses on the special necessities and requirements in each product category. The forestry section, for example, has a detailed guide on the right tire and inflation pressure choice by the application.
Our technical customer service serves all of Nokian Heavy Tyres’ customers and stakeholders worldwide. We provide help, information and guidance in technical tire problems as well as offer product training and handle customer feedback. We are there, where the customer needs us.