Buckinghamshire engineer reinvents the trailer with own unique design

“These big tyres that are kind to soil will only work properly when they are kept flat on the ground,” he says. “And every farm trailer I have seen will not keep a tyre in constant contact with the ground. If they are not bouncing, they are leaning under the strain of cornering forces.

“I believe these are the key reasons they flip over so easily, whether it is a solid beam or a rocking beam axle design,” he adds. “Weight shifts to the outside the tyre as a trailer leans, and this causes the flotation tyre to roll onto its outer edge, and before you know it the whole thing is laid on its side.”

The solution he developed is one that is based on a wishbone suspension system, and uses one wishbone for each wheel. This independent suspension mechanism allows body movement and suspension travel, with movement controlled by a heavy-duty spring and damper.

Opting for a single wishbone has enabled the suspension geometry to keep each tyre totally flat on the ground, as the load sways above it.

“It was a light-bulb moment for me,” he says. “Though it meant starting from scratch with an all-new chassis. Existing designs simply would not work.”

His target was to engineer an 18 tonne, twin-axle trailer for grain and silage, that offered stability unlike any other on the market.

“I bought a pair of secondhand 18 tonne BPW 10 stud axles, then cut them in half,” he says. “I put a pivot on each end of the cut axle, then fabricated a similar piece to provide bracing and create the wishbone shape,” he says. “Wishbone bracing is deliberately angled rearwards to provide increased axle rigidity under heavy braking.”

With maintenance-free, grease impregnated bushings used in the pivot points, he hung the wishbones beneath a 300mm by 300mm central spine chassis. Each wishbone has its own spring and damper assembly working against a top plate, with a securing chain passing through the middle of the spring. This chain prevents the spring falling out and also limits overall movement.

The chassis is also much lower than that of conventional box-frame chassis designs, and this brings additional advantages with enhanced stability. The central spine also provided somewhere to route electrical wiring, plus air and hydraulic pipes – all out of harm’s way.

“The centre of gravity in this trailer is much lower than other 18 tonners, but its ground clearance is also much higher from ditching leaf springs and swapping to wishbones,” he adds.

“But the low chassis meant I had to lift the body by around 300mm to make sure it cleared the wheels.”

Always one to seize an opportunity, Mr Ecob looked at ways to improve the body. And rather than simply sit a box on top of his chassis, he reprofiled the trailer floor, so the middle of the body steps down, to sit on the chassis. This created a gulley in the middle of the floor, to improve emptying and simplify cleaning.

“The gulley has also boosted load volume by about 1.5 cubic metres,” he says. “It also puts load weight closer to the floor, again increasing stability. My trailer does not need to be as high as other 18 tonners.”

The body is damped by high-density rubber blocks, reducing noise as the tipping body is lowered. Radical design elements do not stop there either. Mr Ecob found himself experimenting with a plastic MIG welder, which led him to a skeletal steel body lined with 20mm thick, plastic sheet. Sheets are UV resistant and Teflon coated too, resisting friction and helping material to slide cleanly out when tipped.

“Clever use of materials has found the unladen weight is around 1.5 tonnes lighter than other 18 tonners, which saves on fuel when empty,” he adds. “And with the extra volume too, there is nearly three tonnes of extra payload with this concept. I could probably trim another tonne or so from the unladen weight without compromising on strength or durability.”

Over the last two and a half years, the trailer has done the rounds with a variety of local contractors, farmers and forestry operators. Mr Ecob says the forestry outfit dragged the trailer over 1,300 miles behind a Unimog, and one contractor has punished the trailer over two intensive silage seasons.

“It is still on the same 560/45 R22.5 BKT tyres,” he says. “Tyre scrub is almost eliminated because we are not dragging a bar-axle sideways when turning. The suspension is proving to be so stable, it is rock-solid.

“One customer laughed because it did not have a sprung drawbar – but drawbar suspension is only there to counter axle suspension that does not work properly. My suspension works so well, it does not need a sprung drawbar.”

He says feedback from all that have used it, is positive. “The plastic sides have stopped resonance inside the empty trailer, so noise levels are very low,” he adds. “And because the empty trailer rides well and does not bounce, it is much less noticeable behind you. There is no banging, thumping and crashing from an empty silage trailer that so often dances over the road surface. It is like a ghost.”

Under braking, its stopping performance is reported to be noticeable. “There is no axle tramping or bouncing under braking,” he says. “It is far better than I had ever imagined, and it has been thoroughly over-loaded with no adverse effects.”

Armed with patents to protect his intellectual property, Chris Ecob is looking to find a manufacturing partner to help take his concept to market.

“I have also developed a version that substitutes the springs with hydraulic rams,” he says. “There are opportunities for this concept to be applied to tankers, chaser bins and self-loading bale trailers.

"But I also see this used on large, heavy trailed implements that would benefit from road-friendly suspension. Hydraulic rams would also allow the wheels to be raised off the ground, for field-work.”