14 April 2000

Move to larger tyres as tractors get beefier

By David Cousins

EVER-RISING tractor horsepowers have prompted French tyre maker Kleber to launch a new tyre specifically for tractors from 230-270hp. Ten years ago, such a move would probably have been ruled out-of-court on commercial grounds. But with the rush to bigger and bigger acreages to cut variable costs, tractors of this size are becoming increasingly mainstream.

But rather than go wider, Kleber has elected to go taller. The Topker range tyres are 650mm wide rather than the 710mm of its lower profile tyres. So on ploughing duties they can work in the furrow without running on the turned-over land and on the road they help keep the tractors overall width to within 2.5m (8ft 2in).

But tyre diameter is a hefty 2.05m (6ft 9in), giving a longer contact patch with the soil thats claimed to be some 6% bigger than the patch from a typical 710/70R38 tyre. So wheelslip levels can potentially be reduced significantly.

In fact, Kleber says its own tests showed a cut in average wheelslip from 24% to 14% at the same speed and in identical working conditions.

With tractors above 200hp commonly tipping the scales at 11 or 12 t and a big tool like a 4m power harrow/drill combination adding another 5t, weight-carrying capacity is another key criterion.

Hence the Topkers big load capacities, which are helped by it being a relatively high-profile tyre with a large volume of air in it. Technical manager Robin Audaer says a 650/85 R38 Topker can carry 6580kg/tyre at 1.6bar with 30kph capability – some 850kg/tyre more than the same tractor on 710/70 R38s at the same pressure. Or they could be run with the same loading but at 0.3bar lower inflation pressure.

Kleber has also increased the number of lugs to improve grip in the field and reduce vibration on the road. And since bigger tractor power outputs also increase the force applied to each lug, it has redesigned these to make them tougher.

The new range includes two rear sizes – 650/85 R38 and 650/75 R38, plus matching front tyres in 600/70 R28 and 600/65 R28. Suitable tractors currently (or will shortly) include MF8170/8180/

8270/8280, Fendt 822/844/924/926, SLH Agrotron 230/260,Victory 230/260 and Diamond 230/260, Case Magnum MX220/240/270, Deere 8310/8410/9300/9400, NH8870/8970 and Renault Atles.

Prices? If youre specifying a Topker rather than any other make on a new tractor, the cost difference will probably be all but swallowed up in the overall deal, says Kleber.

If youre retrofitting on to an existing tractor expect about a £200 premium. &#42

Kleber aims to increase grip through use of larger diameter tyres.