The main way of getting the most from your tyres is to run them at the correct pressure for the job in hand. Many of us never check tyre pressure unless it looks flat on the bottom.

In this case, I will be looking at a Continental 520/70 R38 150 A8 which is a fairly standard tyre on a small- to medium-sized tractor. The 520 is the tyre’s width in millimetres (20.8in), 70 is the ratio of the width to the wall height, R38 is the rim diameter in inches, 150 indicates load-carrying capacity and the A8 is the speed rating (40kph).

According to the manufacturer, this tyre can be run at between 0.6-bar (8.7 psi) and two-bar (29 psi), so this will give us our ranges of inflation. These ranges of inflation also differ depending on what width of rim the tyre is fitted on.

The tables supplied by the tyre manufacturers don’t exactly make for fun reading but they offer useful information for inflating your tyres correctly.

Traction is the most important function of most tractor tyres – getting the power to the ground and moving the tractor and implement forward in the field. This is done by the lugs on the tyre, grabbing the ground and using the torque (rotational force) given from the engine through the gear box and differential to push the tractor forward.

From the point of view of traction, the most important factor is the footprint of the tyre on the ground, or lugs on the ground. The lower the pressure you can run the tyre at within its safe-operating range for the weight it is carrying is where the most traction and least wheel slip is available. If the tyre is slightly under-inflated, this will cause flexing of the side walls under the torsional load, which will lead to premature failure of the tyre. Serious under-inflation of the tyre can cause what is known as “bead slip”. This occurs when the tyre starts to rotate on the rim. This damages the bead of the tyre and will also lead to the tyre leaking air from around the bead. If this happens for a prolonged period of time,then the bead may become too damaged to create an airtight seal ever again. So therefore the thought process that the “more lugs on the ground the better” is true to a point, but not always.

Having the lowest allowable pressure for the tyre is also essential to causing the lowest ground pressure from this tyre. The pressure in the tyre is nearly exactly the pressure that is passed on to the ground from the tractor, plus a little extra through the structure of the tyre. In these days of bigger and bigger tractors doing the least amount of soil damage possible is important and using the correct pressure in a smaller tyre can be just as advantageous as going and buying wider tyres.

Reduced pressure in your tyres for field work also has the advantage of making the rolling circumference smaller as the diameter of the wheel and tyre reduces as the pressures drop. This gives the added advantage of greater torque to the ground, as the point of contact is closer to the centre of the hub where the power is coming from.

Over-inflation of a tyre can have serious effects on the ability of a tractor to work in a field. When the tyre is over inflated, the footprint of the tyre decreases drastically from when inflated correctly. This can be an issue when pulling draft loads such a ploughs or heavy-mounted implements where the pressure needs to be higher for transport. Once the implement is in the ground, all the load comes off and the contact area with the ground decreases drastically giving much less traction. In the perfect world, on-the-move inflation and deflation would be used but this is not that common yet. Therefore, using Table 1 for the 520/70 R38, the best compromise needs to be found. This may require the operator to travel on the road at a lower speed in order to have a better field work pressure in the tyres.

For example, if the load being carried by each tyre is 3,000kg, it can be seen from the table that if you travel at 30km/h the pressure required is 1.2-bar (17.4 psi) whereas at 40km/h the pressure required is 1.4 (20.3 psi). So if you inflate the tyres to the lower pressure and drive at the lower speed, you will notice an improvement in field performance.

On the road, the main issue with over-inflation of tyres is the comfort of the operator and wear and tear on the tractor and implements being carried. When tyres are over-inflated, they lose some of their ability to work as suspension. Now that tractors are coming with mechanical suspension, it is very easy to overlook the requirement of the tyres to work as suspension. Just because the operator is comfortable does not mean that the machine is not being damaged by the vibrations and bangs from over-inflated tyres.

Tyre pressures for road use should be the highest they can be for the load being carried but no more. The reason for wanting the tyre pressure higher for road use is so that there is less of a contact area with the road. This lowers the rolling resistance of the tyre which makes it easier to rotate. It also results in fuel savings and less tyre wear.

Running tyres at too low a pressure on the road is the easiest and most common way of damaging tyres. This damage comes from the over-flexing of the tyre walls at speed. This causes the rubber to heat up and greatly speed up the degrading of the tyre wall. The wear pattern will also be affected by running tyres soft on the road, which will wear its lugs but not uniformly. The backs of the lugs will wear down first. This wear pattern will greatly reduce the grip available in the field as the lugs will flex more when wear is uneven.

When it comes to tyres, two basic rules should be adhered to. They should be run at as low a pressure as allowable for field work and as high a pressure as possible and comfortable for road work. This way you get the best traction in the field and the least wear on the road.

Balancing the pressure for a mix of road and field work is not simple, when on-the-move inflation and deflation is not available but a happy medium can be reached.