Tractor operators are always being urged to adjust tyre pressures to the optimum for different combinations of load and speed. It would be a whole lot easier to comply using a central inflation system, says Peter Hill.

Run tractor tyres as soft as the manufacturer’s recommendations allow for the load they have to carry, the level of torque at the rims and the speed they will be going. That, in essence, is what operators of tractors and other self-propelled agricultural vehicles are advised to do.

For a start, they say it will minimise the vehicle’s impact on the soil in terms of compaction. It will also minimise rolling resistance – so less power is taken merely propelling e vehicle along. Finally, it will make the best of the traction for maximum output.

Applying that advice when tractors and vehicles travel on the road for more than just a quick trip to the next field results in more stable handling characteristics, even tread wear and reduced likelihood of cracking in the sidewalls and other areas of the tyre’s tread and carcass.

The trouble is, of course, road travel and field work present two very different scenarios.

Running on tarmac at a decent pace generates heat within the tyre that can become excessive if its structure is forced to repeatedly deform and reform too much thanks to running it too soft. The tyre, therefore, needs to be pumped up a bit harder to reduce the extent of carcass flexing.

In the field, when travelling much more slowly, the tyre can cope with a softer inflation pressure, which allows the tread to plant a bigger area of rubber on the surface and get those traction and anti-compaction gains.

There are clever tyres like Michelin’s XeoBib that are designed to cope with these two scenarios – in other words, it can often be used on the road at pressures more usually confined to the field.

But generally, when tyres are required to support a heavy load (such as a laden trailer or slurry tanker, or a big mounted plough, cultivator or combination drill) at anything more than a snail’s pace over long distances, then field performance has to be compromised by using the correct pressure for the road.

Tractor-mounted compressor

A tractor-mounted compressor is the obvious solution, of course. Except that hard-pressed operators needing to get on with the job are not inclined to drop pressures in the field when they go ploughing and increase them again for the journey home.

Nor is it practical to deflate and inflate repeatedly when shifting slurry in a tanker or muck in a spreader when having to travel by road between yard and field.

The real solution – in an age when operators can alter just about everything on a tractor with the flick of a switch, the prod of a button or a tap on a terminal screen – is automated tyre inflation.

Military trucks

Once the preserve of military trucks – it’s how they manage on soft sand – and the biggest balloon-tyred applicators, auto tyre inflation technology is about to become near-mainstream, as Fendt finalises development of its VarioGrip system.

Operated through the Varioterminal and fully integrated into the tractor’s structure, VarioGrip can be used to alter the pressure of the front and rear tyres in a matter of minutes. Also, if a big slurry tanker has an Isobus-compliant onboard pressure system, it will alter its tyres, too – for maximum flotation in the field and best stability and durability on the road.

The factory-installed system involves an engine-driven air compressor, a pressure control valve for each axle and special hubs incorporating a ring-shaped rotary union through which air can pass from the compressor into the tyre.

There are no exposed air feed lines such as those seen with retro-fit systems on self-propelled flotation spreaders or slurry tankers, and the rotary union is designed to last the lifetime of the tractor, says Fendt.

Tyre pressure can be increased by 1.0 Bar in less than seven minutes; it takes just two minutes to reduce tyre pressure by the same amount and both can be done while the tractor is moving so the process causes little if any delays.

As a safeguard, inflation settings that are too low or too high are brought to the operator’s attention.

Fendt

Fendt engineers have been exploring the system’s potential in the UK in preparation for its commercial introduction. However, suggestions that it could save money by allowing operators to use less sophisticated tyres are misguided, says sales manager Richard Shelton.

Quite the opposite. Using VarioGrip to boost performance and service life by exploiting their low field pressure capabilities to the full gets the best return on investment in more expensive hi-tech tyres such as the Continental Super Volume Tyre (SVT) from Mitas, the Firestone Maxi Traction, Goodyear Optitrac R+, Michelin AxioBib, Trelleborg TM900 High Power and Vredestein’s new Traxion XXL, which can operate at remarkably low inflation pressures while still carrying hefty loads and coping with high torque at the rim.

Challenger

Agco already has some experience of tyre inflation automation, with an optional system fitted to Challenger Terra-Gator application vehicles and the Rogator 600 self-propelled sprayer.

On these vehicles, an external flexible pipe feeds air from the axle hub to the tyre valve and the inflation/deflation valve is operated through the Falcon VT terminal that also operates other functions on the machine.

For simplicity, operators can programme two pressure settings within factory-set limits to avoid inadvertent over- or under-inflation.

Self-propelled spreaders and sprayers such as the S-Trac from South Cave Tractors and the Dammann DT500 can also be equipped with central tyre inflation because they are based on the chassis and running gear of the Mercedes-Benz Unimog.

This is also an external feed design controlled from within the cab to regulate the pressure of all four tyres – either with the vehicle stationary or on the move.

Unimog

It is clearly an attraction for self-propelled sprayers that make frequent road trips back to base to fill up, especially given the Unimog’s sprightly road speed, and is especially relevant to contractors moving often long distances between customers’ farms.

The same applies to ag-spec but otherwise unmodified Unimogs used by contractors as lime spreading vehicles.

The U400, for example, can be driven from a contractor’s base to a customer’s farm at up to 80kph – as long as the tyres are inflated to an appropriate pressure. Once in action, it can operate with a gross vehicle weight of some 12.5t.

In-cab control enables the driver to quickly change the pressure from the road setting to a softer field setting as advised by the tyre manufacturer and minimise the vehicle’s impact on the land.