Compared with their road-going cousins, agricultural tyres have a hard life. One moment they are churning through deep, wet clay, the next they are zipping along a dual carriageway at 50kph.
In an ideal world, tractor drivers would stop to pump up their tyres before heading on to the tarmac and then let them down a bit, before they pull into a field. But putting air into agricultural tyres (and letting it out again) is a painfully slow process and only the truly saintly do it.
However, technology is now riding to the farmer’s aid in the form of central tyre inflation (CTI) systems. These allow air to be put into (and let out of) tractor or trailer tyres on the move via a clever rotary valve.
Uptake of the technology in the UK has been somewhat slow, partly because of cost, but also because there hasn’t been much publicity. But big companies such as Fendt and smaller ones like Tractair and HM Trailers are beginning to make inroads into the UK market.
Longer tyre life
The potential benefits are huge. Turn into the field and you can quickly let the tyres down by several psi simply by pressing a button in the cab. That means much less compaction in the field and better chances for roots to develop.
Finished the field? Press another button as you head from the field to the road and all four tyres will bring themselves up to road pressures. That means less wear on tyres, fewer blowouts, better handling on the road and longer tyre life.
Could a set of tracks achieve the same thing? They can spread the load over a wider area, certainly, and get great traction, but they simply can’t alter the tractor’s footprint.
Keep working, despite of the rain
Ed Lea is a truly busy man. He is a farm operation manager on Sandfield Farms, owned by G's, one of the UK’s biggest vegetable growers. The farm grows 350ha of salad onions, 75ha of dwarf French beans, 200ha of fresh peas, 65ha of runner beans and an astonishing 270ha of asparagus.
With 150 full-time staff and up to 800 seasonal staff - mostly from Bulgaria and Romania - working in the June-to-August peak season, the logistics are mind-boggling. Crops have to be harvested even if the weather isn’t ideal.
“If it keeps raining, we sometimes have to keep going to complete customers’ orders,” he says. “But we have to stop if it’s really hammering down.”
Tyre choice is important
This means tyre choice is vital if the fields are not to become a quagmire. So the JCB loaders that pick up the boxes of veg are now fitted with wider 540/65 R24 tyres and pressures are dropped from 40psi to 20psi to minimise rutting. An astonishing 80 trailers are currently used to get the crop out of the fields and also as welfare units for the workers.
Even if the weather is dry, salad onions have to be pre-irrigated with 10mm of water the day before to make them easier to pull up. That means lower tyre pressures are needed to avoid making a mess. However, once the tractors head on to the road towards the packhouse, they need higher tyre pressures.
The dilemma of needing high pressures on the road and low pressures on the field remained unsolved until Mr Lea spotted a controlled traffic (CTI) set-up at the 2015 Agritechnica show. He then saw Essex company HM Trailers’ prototype at the Cereals event and realised there was now a viable system available.
He bought the first trailer in July and has a second one, with wider tyres, coming this April. Both trailers will have Vredestein tyres with a tread pattern designed to shed mud.
How VarioGrip works
Five 120-liter tanks under the front of the trailer hold pressurised air that can be moved into the six tyres for road transport or into the tanks if you are on the field.
“Getting from fully deflated to fully inflated takes just one minute,” says Mr Lea. “By the time you are up to road speed, the tyre is fully inflated. It’s not tedious at all.”
However, inflating the six tyres without the help of the air tanks would take 20 minutes, he points out.
Single- and twin-line systems are available, points out Vredestein’s agriculture specialist Ed Lonergan. Sandfields Farm has opted for the twin system, which can still run on the road, even if one of the tyres has a puncture. In the cab, a neat box shows the pressure of each tyre and a press of a button changes pressures.
What is the cost?
The 12m long trailer and system costs £25,000, though there is a cheaper version available for £15,000, without CTI.
Mr Lea is convinced this new technology will pay for itself in a single wet year. “In a wet summer we will still not be making a mess - what price can you put on that? I’m confident it will let us get the crop out of wet fields that we couldn’t do otherwise.”
The tyres he chose were Vredestein Flotation pro 560-45 R22.5. They can take a weight of 2t on each tyre at a 17.4psi minimum on the field and can be pumped up at 40psi on the road. They are a direct replacement for a 385-65 22.5 super single.
“The rearmost wheels, which operate passively, definitely follow the tractor better than the fixed wheels,” he points out. “Once you put them into float, they scrub less and go through tighter gateways,” he says. The front pair tend to wear more, though, he says.
Cost of the 6 tyres is £4,200. A substantial investment, Mr Lea admits, but worth it to be able to get in and out of fields without turning them into quagmires. A second unit is on order, he says, and the overall plan is to have 10 of the trailers.
See also: Clever new wheel changer allows for safe tyre swapping
With 567ha of winter wheat, winter barley, oilseed rape, spring barley and spring beans, farm manager Dave Thompson has a busy time of it at Eastury Estates, near Blandford Forum, UK.
Soils vary from clay cap to chalky loams, but there is a lot of flint too, so tyres don’t last very long. “Getting 4,000 hours out of a set is normal, but we would really like to push that up to 5,000 hours,” says Mr Thompson.
However, it’s not just about tyre life, either. He is keen to keep compaction to a minimum, which means altering pressures on the Fendt 828 Variogrip’s Michelin Axiobib IF600/70 R30 front tyres and IF710/70 R42 rears according to the job.
Ideally, on something like the farm’s Vaderstad Swift cultivator, he would like to run with 0.8bar (12psi) all round, or even as low as 0.7bar (10psi).
On the road, Mr Thompson tends to set 1.2bar (18psi) at the front and 1.4bar (20psi) at the back. However, the farm’s heavy seven-furrow mounted plough can require a bit of extra pressure on top of that.
If he didn’t have the central tyre inflation system he would probably just run at a standard 1bar (14psi), he says, though that is probably still lower than most farmers.
There is also a potential benefit in lower fuel use thanks to less wheel slip and rolling resistance on the road, he points out. He says reducing wheel slip from 12% at road pressures to 6% at reduced pressures not only cuts fuel use, but dramatically reduces tyre wear.
“Where I see it fitting in is if you are working on top of drilled land, you can drop your tyre pressures right down and not leave a wheel mark – even with a heavy tractor,” he says.
“Equally, if you are pulling a cultivator or drill and are struggling for grip, you can drop the pressure down a bit and it makes a big difference.”
VarioGrip in-cab display
It is easy to see your tyre pressures, thanks to a neat display in the cab that shows what pressures you have set and what is actually happening on the ground. There is no need to sit around while the tyres are pumped up either, as you can do that as you head to and from the field.
Concerned about pipework snagging on brambles as you go through field gateways? Don’t – it’s all kept very neatly inside the wheel, with a metal cover stopping anything protruding.
“It’s all very integrated and there is nothing to catch,” Mr Thompson says.
Can you see the difference on the ground between a tractor with 12psi tyres and 20psi? Mr Thompson says the difference is easy to spot.
“On our 12m [Cambridge] rolls, you really can’t see exactly where you have been behind the 828, whereas on the smaller Fendt 516 we also have on the farm, you can definitely see the wheel marks.
“We have a 7.2m Vaderstad Swift and a 4.2m Gregoire Besson cultivator, which both take some pulling. We have a lot of flinty soils, too, so reducing the tyre pressures means less slipping and less cutting of tyres in both the treads and sidewalls,” says Mr Thompson.
Cost of the current VarioGrip is about £10,000.