IF and VF agricultural tyres explained

IF and VF are casing classes, not tread patterns. An IF (Increased Flexion) tyre carries the standard tyre’s load at a lower inflation pressure; a VF (Very High Flexion) casing goes further still. You spend that capability one of two ways: less pressure for the same load, or more load at the same pressure.

Everything else behaves like a normal radial agricultural tyre. What has changed is the casing. The sidewall is built to run at far greater deflection, for a full working life, without the heat build-up and casing fatigue that would destroy a standard tyre run that soft.

The convention the industry works to is that an IF tyre carries the same load as its standard equivalent at roughly 20 per cent less pressure, and a VF tyre at roughly 40 per cent less. Read the other way round, at the same pressure an IF casing carries roughly 20 per cent more load and a VF casing roughly 40 per cent more.

Treat those percentages as trade shorthand, not as a specification. What governs is the load and inflation table published for that exact size, casing and speed. Two VF tyres of the same nominal size from different makers will not necessarily have identical tables, and load against pressure is not a straight line — so a flat percentage applied to a standard table gives the wrong number often enough to matter.

Flotation, ride and soil compaction are key considerations. The effect on compaction depends on the soil layer and the operating conditions.

Compaction in the topsoil — the layer a plough or cultivator will move — is driven mainly by ground contact pressure, and contact pressure tracks inflation pressure closely. Drop the pressure, the footprint lengthens, contact pressure falls, and surface compaction falls with it. That is exactly what an IF or VF casing lets you do without running the tyre outside its rating.

Compaction below the depth of normal cultivation is a different problem. Down there the stress field is governed by total axle load, not by contact pressure. No tyre fixes it. The only levers are weighing less, passing less often, and confining traffic to the same lines. A VF tyre on a 20-tonne slurry tanker protects the seedbed; it does not protect the pan at 40 cm.

The secondary effects follow from the same physics: a longer footprint puts more lugs in the ground, so slip falls, more engine work reaches the drawbar and less tread gets scrubbed off. Those are the bonus. Yield protection on headlands and in a wet autumn is what justifies the premium.

Some IF and VF tyres carry an additional CFO marking — Cyclic Field Operation. It applies to machines whose axle load rises and falls through a work cycle: a combine filling and emptying a grain tank, a tanker or silage trailer that leaves the field full and returns empty, a sprayer that empties as it works.

CFO permits a further load allowance above the tyre’s normal field rating, on the basis that the tyre sees its peak load for only part of the cycle and has time to shed heat in between. The conditions are not optional:

• Field use only — the allowance does not apply on the road.
• Below a defined low speed ceiling, published by the tyre maker for that fitment.
• Genuinely cyclic loading. A machine that sits at peak load all day does not qualify, whatever the marking says.

The size of the bonus and the speed ceiling vary by manufacturer and by size, so take them from the maker’s own table rather than a rule of thumb. Older cyclic markings also exist on harvester fitments from before the current convention settled — if you meet one you do not recognise, ask the manufacturer rather than assuming it maps onto CFO.

The prefix sits in front of an otherwise ordinary metric agricultural size, and the load index printed on the sidewall is already the IF or VF value — not a standard index with a bonus for you to add.

Agricultural speed symbols run low: A8 is 40 km/h, B is 50 km/h and D is 65 km/h. A 65 km/h tractor on a 40 km/h tyre is a problem regardless of load. The sidewall decoder breaks any of these down, and the load index and speed symbol guide covers the reference conditions those numbers are quoted at.

An IF or VF tyre in the same nominal size generally mounts on the same rim family as its standard equivalent, and the manufacturer publishes an approved and a permitted rim width range for each size. Check it — a casing designed to run at high deflection on a rim at the narrow end of the range will roll the bead more than you want, and very low pressure on a narrow rim is where beads unseat.

Check the following machine requirements:

• Axle and final drive ratings. The tyre may carry more than the axle is rated for. The lower of the two governs, and on an older tractor it is usually the axle.
• Rolling circumference on mechanical front-wheel drive. Front and rear must stay inside the maker’s lead ratio window. Change one end without checking and you get transmission wind-up, tyre scrub and front axle wear. Run both sizes through the rolling circumference calculator first.
• Clearance. A deflected tyre grows in section width and moves under side load. Check at full lock, against mudguards and steps, and between duals.
• Wheel equipment. Discs, centres and studs have their own ratings. Uprating the tyre does not uprate the wheel.

They carry a genuine premium over a standard radial of the same size, and there are fleets where that premium buys nothing useful.

Buying the casing is the easy half. The benefit appears only when pressures are set from a weighed axle load against the maker’s load and inflation table, at the working speed, and reset when the implement or the ballast changes. That has its own guide: setting agricultural tyre pressure by axle load.