How tyre choice affects soil compaction

Soil compaction rarely shows up as a dramatic failure. It shows up as a field that drains slowly after rain, a crop that yellows in the wheelings, and a yield map with stripes where the sprayer drove. Research on arable soils in Europe consistently puts the yield loss in compacted tramlines at anywhere from a few percent to well over ten percent, and the damage in the subsoil can outlast several rotations.

The tyre is where the machine meets the soil, so it is the cheapest place to intervene. Three decisions make most of the difference.

1. Footprint: pressure at the surface

The pressure a tyre puts on the topsoil is, to a first approximation, its inflation pressure. A tyre at 1.6 bar presses on the soil at roughly 1.6 bar plus the stiffness of the casing; the same axle load on a tyre at 0.8 bar presses at about half that. The load has not changed — the area it is spread over has doubled.

This is why a wider, taller tyre at a lower pressure protects the topsoil better than a narrow tyre at high pressure, and why dual wheels and flotation sizes exist. It is also why a tyre pumped up for the road and left that way in the field is the single most common cause of avoidable compaction.

2. IF and VF casings: the same load at lower pressure

A standard radial tyre needs a certain pressure to carry a certain load without overheating and flexing its casing to destruction. IF (Increased Flexion) tyres are built to carry the same load at about 20 % lower pressure; VF (Very High Flexion) tyres at about 40 % lower. A 710/70R42 that needs 1.6 bar as a standard radial can run at roughly 1.0 bar as a VF tyre under the same load.

The practical benefit is twofold. In the field the footprint is larger and compaction lower. On the road the tyre can still be run at the same pressure all day, so an operator who never adjusts pressure still gets part of the benefit. IF/VF tyres cost more, and the margin is recovered fastest on heavy tractors, sprayers and harvesters that spend real hours on wet ground.

3. Pressure per task: the number on the placard is not the number for the field

Manufacturers publish load–pressure tables for every size. Reading them properly means two figures per tyre: one for road transport at 40–50 km/h, one for field work at 10–15 km/h. The field figure is usually much lower, because at low speed the casing does not build up heat.

A few rules of thumb that hold for most sizes:

• Weigh the axle with the implement mounted or the tank full, not empty.
• Look up the field pressure for that load in the manufacturer's table, then check the road pressure separately.
• If the two figures differ by more than 0.4 bar, either adjust pressure at the gate or consider a central tyre inflation system.
• Never go below the minimum pressure printed on the sidewall or in the table, whatever the load: the bead can slip.

Subsoil compaction: the part pressure does not fix

Lower inflation pressure protects the topsoil. Compaction 30–50 cm down depends mainly on total axle load, and no tyre fixes a 12-tonne axle on wet ground. Where subsoil compaction is the concern, the levers are axle load (smaller tanks, more passes), timing (drier soil) and controlled traffic, with the tyre choice supporting them rather than replacing them.

Where to start

If you are replacing tyres this season, the order of priority for most farms is: fit the widest size the machine and the row spacing allow; choose IF or VF for the machines that work wet ground; and get every operator into the habit of two pressures, road and field. Send us the machine model and the current size and we will list the options that fit, with the load tables for each.