2 April 1999

Six-wheel-drive conversion for better handling

FOUR-WHEEL drive – good; six-wheel drive – better! Thats the theory behind a neat tractor conversion that gives standard tractors more grip, a lighter tread and a lower centre of gravity.

Put together by Lanarks-based JPG Engineering Group, the conversion involves replacing the standard tractors rear axle final drives with fabricated "walking beam" units that use heavy duty chain to transfer drive from the half shaft to hubs on either end of the beam.

This places the wheels equidistant from the original centre line – but because the wheels and tyres are of similar diameter to those at the front, the overall length of the tractor is not increased by any great amount.

"Longer three-point hitch arms have to be fitted to maintain wheel-to-implement clearance," says Graham Clark of JPG Engineering.

"But fitting assist rams would overcome any loss of lift capacity. Power take-off drive is unaffected by the conversion."

First prototypes have been based on MF300 and MF4200-series tractors. But the walking beam axle assembly, designed originally for a forestry timber transporter, will also fit MF Industrial/Fermec torque converter drive industrial tractors.

In addition, the design is being re-engineered for a number of Ford and New Holland tractors.

Test work with prototypes has confirmed some increase in traction from the arrangement, says Mr Clark, although ground pressure and ride comfort are more noticeably affected by theconversion.

"You spread the weight of the vehicle and any load across six same-size wheels and tyres, so the surface ground pressure is reduced, and you get a lower centre of gravity," he says. "The walking beam axles and extra pair of wheels also produce a smoother ride, both on the road and across rough ground."

Turning in tight confines reveals an unexpected bonus – with the rear tyres lifted by hydraulic rams to take the weight off them (or raised from the ground altogether), the vehicle turns on the forward pair in a tighter circle than the standard tractor, thanks to the shorter effective wheelbase.

In addition to prototypes equipped for forestry and related work, JPG Engineering has built a forward control version with central cab (from a mini excavator) up front, leaving a 3m or 4m (10ft/13ft 3in) long space behind it that could accommodate a lime spreader or slurry tank.

"With low ground pressure tyres fitted all round, it would make an effective LGP applications vehicle," suggests Mr Clark.

The mechanical transmission and ready availability of spares and service resources would have particular appeal for some operators, he maintains. &#42