22 December 1995

Trailers weight loss is load capacitys gain

HAVING invested in the high transport speed capability of a JCB Fastrac tractor, Norfolk arable grower Stephen Wright wanted to capitalise on it by hauling the maximum permissible payload.

But, as he found, that is not possible with most high-speed trailers if the total weight of the outfit is to remain within legal limits set down by Construction & Use regulations.

"The extra weight of a high-speed trailer eats into the payload," notes Mr Wright. "We looked at ways of reducing the weight and decided that an aluminium monocoque body was probably the only answer."

Lincolnshire trailer maker Richard Larrington agreed, and set about making a version of his high-speed trailer with enough weight shed to carry a full 14t payload. "Construction & Use regulations allow a maximum gross train weight – for the tractor, trailer and load in other words – of 24,360kg," explains Mr Larrington. "But there is also a maximum gross vehicle weight limit for the trailer and load of 18,290kg. So to take a full 14t load the trailer must weigh no more than 4290kg."

In practice, he points out, steel-bodied high-speed trailers weigh rather more than that – typically 5000kg or more. Knock that off the gross vehicle weight limit and the payload is reduced to 13,290kg.

"A high-speed trailer capable of being used safely behind a Fastrac or Unimog must have commercial vehicle axles to cope with the faster speeds and extra stress loadings as well as provide increased braking efficiency," Mr Larrington emphasises. "Together with a stronger chassis, that can add as much as 1t to the weight of a 14t capacity standard trailer."

Though aluminium is widely used for truck bodies, its significantly higher cost is rarely justified for farm trailers. It is also more difficult to work and needs particularly careful design at points of high stress.

Still, the job was done, and putting the trailer over a weigh-bridge revealed an all-up weight of 4120kg, allowing a handsome payload of 14,170kg. Adding 152mm (6in) extensions to lift the volume a little has increased unladen weight a touch, but the trailer still carries 14t, even though the 6274kg weight of the Fastrac takes the complete outfit right to the gross train weight limit.

Mr Wright reckons the extra cost (£3500) of using aluminium will be paid for simply by reducing the number of trips to the sugar factory.

Stephen Wright: "Getting a full 14t payload will easily cover the extra cost of the aluminium body."

Aluminium is expensive and harder to work with but saves weight. Body extensions were fitted after initial build to increase volume.