3 October 1998


Demands from growers for bigger capacity and faster speeds has meant more sophisticated trailers – but are they worth the extra expense? asks Peter Hill.

RUNNING a standard trailer at the speeds of which a Fastrac or Unimog are capable, not only breaches Construction & Use regulations governing such trailers but is flagrant contempt of the limitations of their designs.

Though question marks remain over some of the finer detail of specifications for trailers built for high-speed use, there is general consensus that they need to be built for the job.

Some specification requirements of high-speed trailers are dictated by law: when used beyond 32kph (20mph) a trailers running gear must be to commercial vehicle standards. For one thing, that calls for a dual-line braking system (either air or hydraulic), not only to deliver necessary braking effort but also to guarantee fail-safe application in the event of tractor and trailer becoming separated.

Other elements – such as chassis strength – relate simply to the dynamics of towing a heavy trailer and load at fast speeds. After all, speed tends to magnify the stresses and strains suffered by components as the trailer encounters bumps and potholes in the road.

A trailer purpose built for high- speed operation is, therefore, a very different beast to its conventional counterpart and its specification will, for the most part, include:

&#8226 twin-line air brakes;

&#8226 commercial vehicle axles and wheels;

&#8226 axle suspension;

&#8226 sprung drawbar;

&#8226 strengthened chassis;

&#8226 tyres to the appropriate speed rating;

&#8226 full lighting;

&#8226 reflective Long Vehicle signs.

Judging by the relevant regulations, such trailers should also be equipped with anti-lock brakes intended to prevent the trailer wheels locking under heavy braking. Many manufacturers do not fit such systems, however, as the reliability and durability of electronic ABS is questionable given the muddy conditions in which these trailers are expected to work.

Usually, it is left to the buyer to decided whether or not to have such systems fitted.

Buyers must also be satisfied as to the strength and durability of components used for suspension, body and chassis assemblies, especially where these are recovered or refurbished commercial vehicle items. Though brand new components have the edge, there is little wrong with using recovered components as long as they are in good condition and have been professionally prepared for their new role.

Safety has to be a paramount consideration in the operation of tractors and trailers capable of fast road travel and should not be compromised by sub-standard components or assembly.

Beyond such considerations, the trailers specification largely comes down to budgets and usage. Air suspension may seem a luxury, but is reckoned to deliver a smoother ride than leaf springs, especially if it can adapt to running empty. Benefits should include less severe impact shocks on the trailer structure, and less load compaction.

Other refinements include steering axles – relevant to conventional as well as high-speed trailers – that make trailers easier to steer in soft or wet conditions and which reduce tyre-wearing scrub on farmyard concrete and trunk road asphalt. With hydraulic lock-up, trailers so equipped can still be reversed up to intake hoppers in a straight line.

Load volume is as important as speed in optimising haulage work rate and costs over longer runs (up to a maximum of 15 miles when running on red diesel and a standard agricultural vehicle licence) and here manufacturers have the challenge of maximising load capacity within the 24t maximum permitted weight of tractor, trailer and load.

With a Fastrac generally weighing in at around 7t and a steel-bodied trailer with chassis and running gear to high-speed specification typically at the 5 to 6t level, the margin that remains is no more than around 12 to 12.5t – rather less than a lighter but slower standard trailer of similar size can take.

One answer is to opt for an aluminium body – rather more expensive than a conventional steel structure, partly because it is more difficult to fashion, but saving crucial weight to boost payloads.

At £4,000 to £5,000 it may seem an expensive means of gaining an extra 1.25t in payload. But for producers regularly hauling a valuable commodity, it adds up to a fair pile and fewer road journeys over the course of a season.

Where a lot of in-field haulage is likely to be included in the trailers workload, it may be better to opt for a bigger volume body at the expense of some road payload capacity. A trailer capable of carrying a 17t load, for example, should be perfectly able to service one of the latest generation tanker beet harvesters on its own, given a field-to-pad haul of no more than 2.5-3km. And, as long as weight limits are observed when it is used on the road, such a trailer remains perfectly legal.

A high tipping angle is the latest development for beet hauling trailers. As an alternative to a purpose-made scow-back dumper but capable of handling grain and other loads with equal efficiency, the 60í tipping trailer, with hydraulic tailgate set to 2.74m ground clearance, will leave a level-topped pile of beet to the recommended depth for storage.

See more