7 June 2002

Wrong tyres make for bumpy ride

Poor ride quality, uneven

wear rates and bad handling

could all be characteristics

of having the wrong tyres

fitted to your tractor.

Geoff Ashcroft spoke to

Michelin about correct tyre

management

FOR many, buying a new tractor is often meticulously planned with optional extras thoroughly studied before key components are added to a side order list.

But when it comes to choosing wheel and tyre options, few give the subject the level of attention it deserves, says Michelins agricultural technical manager Keith Baker.

"Buyers will often compromise on their chosen specification and take a tractor from dealer stock simply because it is available that day and at the right price, even though it may be on the wrong tyres for their workload," says Mr Baker.

"When buying any piece of farm machinery, be it a tractor, trailer or implement, farmers should seek advice from the tyre industry."

"Tyres are often the least thought about aspect when buying a tractor," he explains. "It is not until the tyre industry gets complaints about poor ride quality through bouncing or pitching, and accelerated wear rates, that we are able to advise users about selecting the right tyre to suit their circumstances. But at that stage, switching tyres can become expensive."

Mr Baker also says many users are still not switched on to the benefits of adjusting inflation pressures to suit loading. "Its not uncommon for tractors to be supplied to a dealer with over-inflated tyres to counter any bouncing when tied down during shipping, but few will take the trouble to check and reduce the pressures before a customer gets his machine," he says.

Users need to manage loads, speeds and pressures to get the best from their tractor and implement tyres, reckons Mr Baker.

"Air is the key with any radial tyre. It is fundamental in carrying the load and allows side walls and tread casings to work effectively," he says. "And pressures should be checked at least weekly."

Slow punctures are the source of premature tyre failure. "They can be easily over-looked and on a tandem axle trailer, one slightly soft tyre wont look obvious. But running down the road at up to 65kph with a fully laden trailer will cause that soft tyre to get hot, which will in turn lead to a breakdown of the tyre construction. Disintegration or tyre explosion will quickly follow," he warns.

Michelin can for example, offer up to 10 different rear tyre choices, matching them with front tyres for any particular model and size of tractor. Each tyre type offers a different level of performance, ride quality and longevity.

"The majority of our tyres can handle speed ratings of up to 50kph to suit the growing number of tractors with faster gearboxes, while our high speed range for Unimogs and Fastracs operating at up to 65kph, is much more specialist and limited in choice," he says. "Our high speed tyres also have additional components in their construction which can mean added cost to the customer."

Mr Baker reckons that fitting low profile tyres are a low-cost, simple upgrade that many farmers should consider because they do not require wheels to be changed. The advantages they can offer over a standard tyre are considerable.

"The ability to carry greater loads at lower inflation pressures is beneficial to soil structure and it can often result in improved traction," he says. "But they will be less suited to the front axle of a tractor equipped with a front-end loader."

In response to the ever faster road speeds being adopted by tractors, the firm has recently introduced a high-speed trailer and implement tyre called CargoXbib. With a 65kph speed capability, CargoXbib uses a different construction in its tread bracing, which allows high speed use and greater load carrying ability at lower inflation pressures.

With a chunky tread block pattern, the CargoXbib also offers improved flotation characteristics and a lower rolling resistance. The 600/55R 26.5 tyre – smaller sizes are due to follow – can carry 5150kg at 65kph with an inflation pressure of four bar. Yet for maximum flotation, its pressure can be dropped to one bar, though its maximum load carrying potential is then reduced to 4200kg.

"The agricultural market is so complex and specialised, that no one tyre option will provide the best result on every job for every machine," he says. "As a manufacturer, we have to consider traction, tyre life, cost, compaction and comfort, and offer a range of tyres that provide different levels of performance in each of these areas to suit the needs of the agricultural industry."

"Such criteria makes specialist technical support from the tyre industry even more important to the end user," he says. &#42

"As tractors get faster and faster on our roads, be sure to adjust inflation pressures to suit load and speed," warns Keith Baker, Michelins technical manager for agricultural tyres.

Maintaining correct tyre pressure on fully laden trailers is imperative if they are to be run at high speeds up to 65kph, says Michelin. Inadequate tyre pressure can cause breakdown of the tyre construction and lead to blow-outs.

This spacer band for Stocks dual wheels now has a double bevel around its circumference to increase its strength and rigidity. This, says the company, is in response to the trend towards more powerful tractors and heavier implements which now require extra strength. Bevels are rolled into the spacer bands using a special machine – bands up to 250mm wide use 5mm steel, while wider bands use 6mm.