Even preparing for a wet harvest might be tempting fate, but there’s some good sense behind it. By the same logic used by people who carry umbrellas to stop it raining, being ready and kitted-out for a wet harvest should guarantee a bone-dry one.

So what can you do to keep harvesting in a year when the corn may be dry but the ground underneath is soggier than week-old semolina?

Wide wheels

An obvious way of spreading your combine’s weight is to go for bigger wheels and tyres either by going wider or taller, although you may be limited by axle clearances for the latter.

While large, modern combines are likely to have 800mm-wide tyres as standard, smaller, older machines tend to top out with 650s. A second-hand set of 800 x 32 wheels from a combine breaker is about £1,750.

Dual wheels

Clamping a second set of wheels to the combine’s existing rubber can be one of the most versatile solutions, as they can be quickly whipped off for transport. However you’ll get furrowed brows from manufacturers, who generally don’t approve of the practice because of the extra strain it puts on the axles.

At the beginning of July last year artic-tractor specialist John Nicholson was trying to work out a way of disposing of the unwanted sets of duals that the big American tractors he imports arrive on.

Many articulated tractors’ wheel rims are 32in in diameter, like the majority of combines. So a set of 650mm-wide tyres from a big American prime-mover is relatively easily grafted on to the combine’s existing rims. But up until 2007 there hadn’t been too much demand for that.

“Generally UK farmers want a decent set of single flotation tyres so we end up with a heap of duals,” he explains. “I stuck an ad in Farmers Weekly to see if I could shift a few sets for £150 a pair.”

Just as the advert appeared the heavens opened. Within seven days Mr Nicholson’s yard was empty, having sold 84 pairs to farmers desperate to keep their combines afloat.

Given that combine axles are not generally rated to accommodate duals, Mr Nicholson advises anyone fitting extra sets of wheels to run the outer tyres 2-3psi lower than the inners to provide a bit of flex as the machine rides over lumps and bumps. This year his stocks are low but he says he’ll always try to find ways of sourcing wheels should they be required.

Dual wheel specialist Stocks Ag supplies extra rubber for all manner of machines and offers two options for combines.

“You can fit duals exactly the same size as the existing wheels but that puts a lot of strain on the axles, hubs and studs, plus it’s pretty expensive,” explains the company’s Rick Parker.

“We recommend what’s called a ‘step-down’ dual using a different size rim with tyres of a similar diameter to the rubber that’s already in place.”

This gives the opportunity to fit cheaper tyres with a rim that still fits the existing 32in wheel.

As an example, a set of 20.8R38s will set you back £2,750, with clamps and eye-nuts included. A word of caution however: if you don’t want your duals turning up after harvest, order early as Stocks needs six to eight weeks’ notice.

Claas’ factory-fitted Terra Tracs have been available for the German manufacturer’s biggest combines for more than 10 years and now more than 70% of Lexion 560s, 570s, 580s and 600s are sold on rubber tracks. When you look at the advantages, you begin to understand why.

“There’s a 66% reduction in ground pressure when compared with 900mm-wide tyres,” says Claas combine specialist Paul Moss.

“But it’s not just that lighter footprint that you gain. There’s much more traction on tap for hill-climbing and the machine’s overall width is that much slimmer for the UK’s narrow lanes.”

In addition, when you come to sell your combine after five years’ work, he estimates that a tracked machine will command a £5,000-£10,000 price premium. That makes the £22,000 track price look a lot more attractive.

New Holland started offering Tidue Amfibios retro-fit rubber-tracks for its combines in 2007 and has sold 10 sets. Later this year a version with suspension will go into production and New Holland dealers will be able to offer the tracks for fitment to any colour combine.

With a range of track units suitable for tractors and combines, Soucy tracks are imported to the UK by Case IH dealer Collings Bros based at Abbotsley, Cambs. A standard set for a harvester will set you back about £30,000.

Up until recently John Deere had included Bruko track-units on its option list but the agreement with Italian manufacturer Grecav has since come to an end. Deere says it is currently working on an alternative solution.

Tracks – pros and cons

Pros

• Reduced compaction

• Increased traction for hill-climbing

• Improved comfort on road

• Reduces machine width to between 3m and 3.5m

• Improved residual values

Cons

• Cost – between £20,000 and £32,000

• Risk of scuffing if headland turns too tight (unlikely with wide headers)

Warwickshire farmer Richard Ward’s experiences last harvest proved to him just how important rear-wheel rubber is.

Having already fitted duals on the front, he added some taller, rather than wider, rear wheels with the aim of increasing footprint and reducing rolling resistance.

“The theory was right but in heavy going the taller tyres just acted like anchors,” he says. “We needed something that didn’t exert as much drag because the duals were clogging with mud on the front.”

So he sourced a set of wide wheels from the front of a John Deere tractor to sort the problem.

“The Trelleborgs made all the difference. Even without the duals they kept us afloat. Without a shadow of a doubt it had been the rear wheels bogging the combine down.”

But he adds a few words of caution: “We had to make sure the steering ram stops were adjusted to stop the tyres clashing with the tinwork. The steering also gets pretty heavy. This year I’m hoping to adapt the steering linkage so that the rams have got more leverage on the wheels.

“That will mean it’s more turns lock-to-lock but there will be more power to turn.”

Running the tyres at low pressure also highlighted another problem. On banked ground the sideways forces meant that there was a danger of the beads running off the rims. Mr Ward advises running the rear tyres at 25psi in such circumstances.

As for his duals, he found that four clamps just weren’t enough to firmly clasp the wheels together under such high stress loadings. He ended up having to keep tightening them to stop them slipping. This year he plans to introduce a locking device similar to that found on American articulated tractors to brace both wheels rigidly together.

Look at a stubble field after harvest and the most obvious causes of compaction are the trailer wheelings. Often that’s because they’re equipped with HGV-type “super-singles” which have a tendency to bury themselves at the first opportunity.

Not only does that mean they take a lot of pulling in the field but getting rid of the damage they do can be really thirsty work.

Andy Hipkin from tyre supplier Fieldens has noticed a marked increase in the number of people switching to wider flotation tyres on trailers.

“We receive more and more calls from people looking to ditch their 15in wide super-singles running at 70-80psi in favour of 22in rubber that can operate at less than half the pressure.”

“Of course you’ve got to take underbody clearance and inter-axle spacing into account but you can get a set of four 560/45R28s for between £1,600 and £2,400 – you’ll save that in diesel in just one year.”

Driving a combine harvester when things begin to get slippy is an art form all of its own, says John Deere combine specialist Mark Smith.

“Because of the nature of hydrostatic transmissions, very often operators don’t realise how much wheel-slip and sinkage there is until it’s too late,” he points out.

“Instinctively, as forward speed starts to slow, you want to push the lever forward but that’s actually the worst thing to do – back off while you can.”

Carrying the majority of the machine’s weight, the front wheels are always the first to hit the wet spots, so pulling back as soon as you realise your wheels are spinning is good advice.

Should the worst happen, pulling the harvester out of a wet hole is a task that requires more than a little thought and done wrong can cause a lot of damage.

“Last year we heard some horror stories of chains being wrapped around rear axles and combine chassis being bent,” says Mr Smith.

Last year even tracked machines weren’t immune from getting stuck and being damaged during recovery. When they do bog down, it takes a lot more effort to pull them out because of the smaller diameter of their front and rear track-drive-wheels.

“Follow the maker’s guidance and always aim to hook up the chain somewhere on the front axle to gently pull the machine out backwards.”

John Deere combines can also be towed from the header trailer clevis but this is not recommended for other brands.

Often tyres are still at their delivery pressures of 30-40psi when they should be more like 20-30psi. Getting that right should be the first step to take in ensuring a smooth harvest.