17 October 1997


A sprung seat and cab on rubber blocks is about as far as most

tractor manufacturers go to give drivers a comfortable ride. But

the situation looks set to change. Mike Williams reports

TRACTORS with some form of suspension have been available for years, but ride improvements and other potential benefits of using springs to reduce shock loads have only recently attracted enough interest to make an impact on sales.

When Silsoe Research Institute developed the first fully-suspended tractor cab in the early 1980s, manufacturers gave it the thumbs-down and said it would not attract customers.

This was followed by Renaults Hydrostable cab – the first production tractor cab with a proper suspension. Announced in 1987, it impressed the RASE Machinery Award Scheme judges who selected it for the 1989 Gold Medal. Persuading UK customers a cab on springs was a good idea took longer, and four years ago only 15% thought the benefits were worth the extra cost.

Since then sales of Hydrostable cabs in the UK have taken off and to date account for 54% of Renault tractors sold.

Renaults suspension consists of four coil springs with shock absorbers plus torsion bars to isolate the cab from the rest of the tractor. The aim is to absorb shocks as the tractor wheels roll over uneven surfaces, giving a smoother, more comfortable ride to reduce stress and fatigue.

Putting the suspension on the front and rear axles means most of the tractor is on springs, and not just the cab. This was the system JCB adopted for its Fastrac. One of the problems it faced, was providing a suspension which allowed ploughs and other rear-mounted implements to work efficiently with draft control.


Front suspension for the Fastrac is two coil springs with telescopic shock absorbers. At the rear, JCB used hydro-pneumatic technology from the car industry for the self-levelling suspension. It adjusts automatically, levelling the tractor laterally and longitudinally when equipment is mounted on the front or rear. It is a system which helped the Fastrac to earn a reputation for heavy draft work in addition to higher transport speeds on the road.

Both JCB and Renault claim increased work rates for tractors using their suspension systems because of improved driver comfort. This is borne out by research showing that factors limiting tractor speeds include driver discomfort.

JCB claims work rate increases of up to 30% for some secondary cultivation jobs, based on tests carried out by ADAS. Whereas Renault claims its Hydrostable cab allows some field work speeds to increase by 20% before driver fatigue thresholds are reached.

With tractor suspension winning new customers, more companies are developing systems of their own. Fendt Favorit 800 series tractors from 165hp upwards have a cab suspension with springs and shock absorbers to reduce vibration and longitudinal movement, plus a transverse stabilising rod to control lateral movement.

Fendt has also developed a hydro-pneumatic suspension system for the front axle. This uses spring loaded nitrogen reservoirs to absorb shock loads carried from the wheels through a hydraulic ram. The result is said to be a smoother ride for the driver plus improved steering control when travelling at speed over a rough surface.

It would not be surprising if some of Fendts suspension technology eventually appears in the MF range, now that both brands are owned by the same company.

Same Deutz-Fahr showed a tractor with experimental cab suspension at last years Smithfield Show, but this may be overtaken by the launch of the Deutz front axle suspension announced in July. The system uses two gas-filled rams and three nitrogen-filled cylinders to absorb shock loads from the front wheels. It is an option on Agrotron tractors over 100hp, costing about £5000.

Axle manufacturer ZF has recently demonstrated a front axle suspension system and reports serious interest from some of its customers.

Tractors exception

Few vehicles do not have a proper suspension system, but farm tractors – which often travel over rough ground – are an exception.

Numerous surveys have linked agricultural work with a relatively high incidence of back problems. Farm work can mean exposure to wet, cold weather, lifting heavy loads and being bounced on a tractor seat, and these are factors which can cause problems from back aches to severe spinal damage. It is not clear which is the biggest cause of problems, but vibration experienced by tractor and machinery operators is considered to be a major factor.

The DLG research organisation in Germany investigated vibration experienced by tractor drivers in a project supported by Renault. They used two 145hp Renault tractors, one with a conventional cab on rubber blocks and the other with a Hydrostable cab.

Results showed vibration in the conventional cab can cause stress after two hours, but vibration in the suspended cab was reduced by up to 35% allowing twice the number of working hours before stress is a factor.

Although precise links between health problems and vibration in the cab are difficult to measure, the situation is already causing concern at the Health and Safety Executive. Last year an HSE information sheet about exposure to vibration caused by tractors and machinery included a league table of driving jobs ranked by vibration levels they cause, and there was also a suggested maximum number of hours drivers should be exposed to these vibration levels each day.

The HSE data put baling, power harrowing and driving a combine harvester among the least causes of vibration for drivers, and no time limit is suggested. Fertiliser spreading, spraying and general transport are all near the top of the exposure scale, and the suggested maximum driving time is just four hours a day. Hay tedding carries the highest level of vibration exposure and the HSE suggests a three-hours work limit.

"Every tractor should be like the Fastrac and have a proper suspension," according to Hertforshire contractor, Stan Dodson.

He runs one Fastrac 1135 and three "conventional" tractors in his contracting business based at Whempstead, near Ware, and the Fastrac is the tractor he likes to drive. The best feature is the suspension, he says, and he thinks there is nothing to beat it.

"We do a lot of baling, and that means working long hours in the summer," he says. "Being jolted about on a tractor may not matter when you are young, but it affects you more as you get older. I dont mind working long hours, but I want a smooth ride and the Fastrac is the most comfortable tractor Ive driven."

Safer on road

Because the suspension helps to smooth out bumps, its also safer on the road, he says. "The steering is much better because of the suspension on the front axle. Its steadier with less jolting on a rough surface, and that reduces the risk of an accident."

For much of the year tractor driving is almost a full time occupation for Suffolk contractor Mike Gooderham. He specialises in whole farm contracting, and currently provides a year-round service on farms totalling 1400 acres.

Renault provide most of the power for his business at Hall Farm, Stoke Ash, Eye, and one of the features he likes is the cab suspension. His latest tractor, a 165hp Ares 720RZ – is equipped with the Hydrostable cab.

"I wasnt really interested in the suspension until I bought a 180TZ model which happened to have it fitted, and I liked it as soon as I tried it," Mr Gooderham explains. "The best way to try it out is to drive it – the ride is smooth."

James Clutterbuck, a college student completing a work experience year with Mr Gooderham, is also enthusiastic about the suspension. There are plenty of situations where you can drive one or two gears faster than an ordinary tractor, he reckons.

"There are three settings for the suspension on the Ares models, which is an improvement over the earlier Renaults," he says. "The 720RZ was on the softest setting when it was delivered, and it has stayed there because it gives the smoothest ride." &#42

Above:Suffolk-based farm contractor Mike Gooderham (left) and James Clutterback with the 165hp Renault Ares tractor. Right:One of the four springs that make-up the Renault Hydrostable cab suspension.

Front axle suspension is now available for Deutz-Fahr tractors of 100hp plus.

Fendt 800 series tractors have front axle and cab suspension systems.

See more