21 May 1999

More to it than getting to

grips with it

Tyres – little moves with

out them. Goodyear believes

tractors will move a little

easier with its new DT812

range. Andy Collings

reports from the companys

technical development site

in Luxembourg

IT is often said that tractors are only as good as their tyres. All the horsepower in the world can count for nothing if it cannot be effectively channelled through a machines tyres.

Such details are not lost on tyre manufacturers which, in the main, strive to provide the agricultural industry with a range of tractor tyres capable of turning in good performances where grip is concerned.

But according to Goodyear, there is more to tyre manufacture than just providing good grip. Factors such as ground pressure, durability and on-road performance are now increasingly important as tractors become faster, heavier and more powerful.

Goodyears latest introduction comes in the form of the DT812 tyre range – a range comprising some 20 sizes from 360/70R20 120 A8,B to 620/70R42 166 A8,B. Speed rating is 50kph.

"A tyre offering both comfort and efficiency," is how the manufacturer chooses to describe its new product – comfort from a new design of sidewall, and efficiency from the shape and angling of the lugs.

So, to start with the business end of the new tyre – a closer look at the lugs. When compared to earlier Goodyear tyres, the DT812 has more of them, which improves ride comfort, and their new, self-cleaning, curved shape is claimed to provide an "aggressive" gripping action in all conditions. A reinforced lug base is claimed to help prevent damage to the tyre carcass.

Low ground pressure – much as can be made possible with large tractors carrying heavy implements – is achieved by the DT812s low aspect ratio which is said to provide a large, evenly loaded foot print area.

Having, it is hoped, designed a tyre which could offer a high degree of operating efficiency, Goodyear designers turned their attention to incorporating an operator comfort factor.

Details such as vibration and excessive bounce were rarely major considerations in the past but with tractors now travelling at faster speeds with heavier loads, they have come increasingly to the fore.

It may appear obvious, but the key to preventing many of the travel irregularities experienced is to ensure that the tyre is round. According to Goodyear, this is not always the case with some tyres and the problem can be further compounded by using poorly formed rims.

Goodyear, with its advanced moulding techniques, would claim its tyres are round but concedes that, with little if any control over rim production (other than random quality checks) there may still be problem cases.

With one or two notable exceptions, the vast majority of tractors still rely on tyres to act as its main – or indeed only – means of suspension and effective sidewall deflection is incorporated into the DT812s construction.

In terms of durability, the company claims the tyres design offers improved wear – when compared to earlier models – and better resistance against chipping. And for those who need to monitor tyre wear, several of the lugs are marked with 0%, 25% and 75% wear marks.

Goodyear points out that the demands made on modern tractor tyres are now higher than in most other operating climates and are comparable in many ways to those experienced in heavy construction duties.

To this end, the company reports it is considering using similar rubber compounds used in construction-type tyres – possibly for later versions of the DT812 tyre.