Air pressure key to tractor tyre performance


Most farmers know a tractor runs better and more economically when correct tyre pressures are maintained. But do you maintain correct pressure? According to tractor tyre experts, the incidence of under-inflation of farm tractor tyres is immense. Source: The Weekly Times

Too often farmers take the “she’ll be OK” or “I think they’re about right” approach. It’s akin to needlessly throwing money down the drain.

Inevitably, not taking a few moments to check for the correct air pressure in tyres becomes a habit, and before long tractor efficiency drops alarmingly while fuel costs rise. Equally upsetting, when treated this way tractor tyres wear excessively and give up well before their time.

“Your tyre is designed to have a certain shape under load and if that shape is stretched you get over-inflection or under-inflection,” says Russell Kennedy, a technical advisor with Australian Tyre Traders.

Too little air in a tyre can lead to sidewall cracking, bead cracking and tread lugs becoming torn around the edge. Similarly, too much air in a tyre will result in a smaller footprint, causing increased soil compaction and a rougher ride. It can also lead to rapid wear and/or tyre failure.

“You get farmers who religiously check the oil, for instance, because they know if they don’t and the oil gets down a little bit it will cause damage to a motor,” said Michael Armstrong of the Tractor and Machinery Association of Australia and a consultant to the Trelleborg Group.

“It’s the same with air. If you don’t check the air in tyres regularly, it can get down and the tyre will start going into overload and you will destroy the tyre.”

Often such a costly failure can be prevented with regular use of a cheap pressure gauge.

“Pressure gauges range from about $8 to $18 and they can save you a lot,” Russell Kennedy said.

“Let’s say we have a tractor with equal four-wheel-drive with eight tyres on it. Say the tyres cost $4000 each, so that’s $32,000 all up.

“If you buy a $9 gauge and set your pressures, you can expect to get full performance out of those tyres.

“But if your pressure is not right and you blow one or two, then it’s a big loss, and you will have trouble later matching up the old and new tyres.

“A $9 gauge is pretty cheap insurance.”

The experts blame ignorance, laziness or common misconceptions about tractor tyres as the major cause of tyre damage.

Too often, says Mr Kennedy, farmers fail to comprehend the many variables that need to be considered before deciding on air pressures. These include a tractor’s weight splits, the weight of attachments, the loads placed on the drawbar or three-point linkage, the job being undertaken, and the operational speed of the tractor.

One of the biggest misconceptions, say the experts, is that tyres carry the load of a tractor.

“They don’t – it’s the air in the tyre that carries the load,” Michael Armstrong said. “You can have a tyre that, say, has a 5000kg capacity and the manufacturer will state ‘this tyre can carry 5000kg at this air pressure’.

“If you run that air pressure you can expect the tyre to carry that capacity. “But if you run 20psi less than that pressure, because there’s less air in the tyre and because it’s the air that carries the load, the carrying capacity of the tyre will come down.

“At the reduced air pressure the tyre might only carry 3000kg. And if you try to carry 5000kg, the tyre will go into an overload situation.

“You know, the tyre is a pressure vessel, that’s all it is. If you take the air out of the tyre what happens – it’s flat, so it has no carrying capacity.”

This applies equally to both front and rear tyres.

Mr Kennedy advises calling in a tyre expert if you can’t determine your tractor’s optimum tyre pressures under different situations.

Today’s tractors need to be versatile and far more are being fitted with front-end loaders. Yet front-end loaders, combined with operator ignorance, are responsible for much tractor under-performance and tyre wear.

About three quarters of damaged tractor tyres coming back to dealers via warranty claims involve tyres on tractors with front-end loaders.

A front-end loader can put excessive weight over the front axle of the tractor and, if the air pressure hasn’t been adjusted accordingly, a tyre can be destroyed.

“There are a lot of machinery dealers and a lot of owners who just don’t put the right pressure in the tyre to carry the load, and then the tyre fails not because of a fault in the tyre but simply because it was running half flat,” Mr Armstrong said.

Another problem for tyres is that farmers sometimes forget, or just can’t be bothered, to change tyre pressures according to the job at hand. This often occurs when different jobs demand different implements.

“We have a lot of farmers who have a dual configuration when doing their seeding, and then when they come to fertilising and want to run between the rows, they take off the duals but don’t change the tyre pressures,” Mr Kennedy said.

“I’m not trying to scare anyone but there are just a few things you need to know about tyres and how to set up your tractor.”

While many farmers add water to tyres as ballast to aid traction and tractor balance, it’s not recommended with newer tubeless radial tyres.

“If you put water in a tubed tyre, it’s contained in a bladder – but with a tubeless tyre you don’t have a buffer between the water and the rim, and you get rust bubbles,” Mr Kennedy said.

Plus, adding water to a radial tyre negates one of its greatest attributes. Water is largely non-compressible so it reduces a radial tyre’s flexibility, which in turn reduces traction. Even adding water to cross-ply or bias-ply tyres is an “ignorant, low-tech” way to gain traction, say the experts.

If an application demands extra weight on a tractor, a far better option is to use “suitcase” weights fitted to the front or rear of a tractor.

Likewise, the experts advise against fitting tubes to tubeless tyres, maybe to keep a punctured or damaged tubeless tyre in operation.

While this ploy can sometimes work, the tube can cause friction inside the tyre, leading to further damage.

Tyre maintenance is also about keeping tyres clean and free of caked mud or petroleum products that can cause damage. If that happens, Mr Kennedy warns against patch-up repairs.

“You can repair a tyre tread and sometimes you can put a patch on the sidewall, but it’s superficial,” he said.

“If the tyre has got to flex or stretch and you put a patch in the wrong place, the tyre will leak or blow.”

He also warns that European tyre manufacturers make pressure recommendations based on European conditions, which can cause problems in Australia’s tougher conditions.

“Our soils are different. We have black, grey, red and brown clays here that sometimes go down two metres, so you have a hard application. If you put a really soft tyre on that it can be worn out in 200 hours,” he said. “Most farmers have a preferred tyre dealer so they should talk to them if they are in any doubt.”