Are you sitting comfortably?
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enthusiastically for its non-reflective instruments which "stand out clearly when lit at night, yet don't irritate the eyes."
Roy thought the Chapman Bremshey seat "gave a good ride", and was particularly impressed with the headrest which gave "good neck support". But Roy thought Roadtrain's clutch "tended to be heavy in traffic".
The little things in the Leyland cab pleased Roy most, like the interior lights, the toolbox-cumfootrest, and rubber flooring, which makes cleaning easy.
Down at the Gate café on the A2, we found Scot Robert Adams of BXL Plastics Limited who was stopping for a bite to eat on his way back to Grangemouth from France. Robert was driving a Cummins E290-engined Foden Fleetmaster pulling a bulk powder carrier and he had unqualified praise for the Foden.
"I couldn't fault the wagon in any way," he said, pointing out it was economical and comfortable. Robert moved from a DAF to his current tractive unit, and after a year of regularly driving the Foden, he wouldn't willingly go back to a DAF, "Fodens are on to a winner with the Fleetrnaster. If they had introduced the S10 cab a year earlier, I'm sure they wouldn't have gone bust" Back at Farthing Corner once again we found mostly Continental vehicles. Tony Ellis, known as Leadfoot to his friends, drives a T registered Mercedes-Benz 1626 for Math Verdegaal and had just returned from Belgium with a load of bananas.
"I'd prefer a full sleeper to this M cab," he said, "but generally the Mercedes is comfortable." There was no suspension seat in the Mercedes, but Anthony. be, lieves that one wasn't needed. In his opinion, the 1626s chassis and cab suspension is quite adequate. "I think the ride is better than either a Volvo F10 or Ford Transcontinental, both of which roll too much.
"This is the first Mercedes I've had and while I would prefer this cab to a Volvo, it would be nice to have the same amount of power as an F10." A feature of the Merced Tony really appreciated vs air outlets on the outside doors that kept the windows clean.
Time restrictions didn't us to include examples oi kind of vehicle on the ma our survey.
A statistician might sz poll thus has no "statistic nificance"; but a comp sive national opinion poll ers would probably only s confirm the impressil gained that more drivers tisfied with the standard comfort now than they s few years ago — but a fe gling areas of complaint rr As technology advanci manufacturers move I learning curve, it becorr creasingly difficult for I (and lorry drivers) to q degrees of cab comfort, tive assessment of ride always interests a manufa but isn't much help to designing a cab.
The basic problem wi commercial vehicle is tf main function of chassis s sion is to cater for the loac can vary between nothir maybe 20 tons. Compa this a driver's weight repi an infinitesimal increase, 3ostrom Europe Paul Holdsworth irgues that the most costffective way of overcoming the woblem is to fit a suspension ;eat which then has the sole pur)ose of isolating the driver from he vibrations which cause liscomfort.
To find out more about these ribration frequencies and to see .iow the seats do their job, I risited Bostrom's European leadquarters at Northampton, ust a few months before its new :9m manufacturing plant goes nto action_
In explaining how its seats vork, Bostrom refers to a publi:ation by a committee of the Inernational Standards Organisaion which attempts to define vhat constitutes an acceptable vorking environment. It has iswed an international standard IS 2631) which establishes the elative importance of four as)ects of vibration: frequency, implitude and direction of vibraion, and duration of exposure.
The standard has taken many 'ears to compile and it can't be ,ummarised here. But it is in
teresting to note that ISO standards already exist for farm tractor seats and EEC directives have been issued for two classes of tractor seats.
It is quite likely that similar standards and directives will soon be applied to cv seats.
As the graph above shows, a conventional or static seat cannot isolate a driver from the most undesirable vibration fre quencies in the same way a suspension seat can. "Transmissibility" may be translated as the ratio of input to output of vibration— or a comfort factor, if you like.
At three cycles per second (a common frequency, for example, in an unladen articulated vehicle), a suspension seat can reduce vibration reaching the driver by 40 per cent whereas at that frequency a static seat actually amplifies input vibrations by 245 per cent.
In other words at this frequency, a driver would be better off without any seat at all rather than with a static one.
ISO recommendations show that the human body is least tolerant to vertical vibration in the frequency range of four to eight cycles per second and our graph also shows that a suspen sion seat is very effective at isc lating a driver in this frequenc. range. But at high frequencies above about 12 cycles pe second — the static seat is actu ally a more effective isolator.
When a manufacturer such a Bostrom tunes a suspensioi seat to suit a particular vehicle'. suspensions's characteristics the two major variables are thi seat's hydraulic damper and thr spring rate. Bostrom uses tor sion bar springs in most of it commercial vehicle seats but ir the latest top-of-the-range 700 Series, air springs are used — ai is supplied to the seat from thr vehicle's normal air supply.
Apart from its excellent by frequency vibration isolatior characteristics, the main advan tage of the air suspension seat that it is self-levelling. It is auto matically brought to the middlf of its 100mm (4in) total vertica travel irrespective of the weigh of the driver and without an) effort on his part.
The other new interesting fea tures of the 700-Series are a fore and aft isolator and a variable lumbar support. As the name suggests, the fore and aft isolator provides the driver with seat suspension in the horizontal plane. It allows ±25mm (lin) of movement and can be locked out using the normal fore and aft position adjuster, when it is not required when parking, for example.
Its main function is to isolate the driver from the cab nod or back-slapping which is prevalent in some vehicles.
The variable lumbar support seems an excellent idea. Its operation is simple. A rubber sack is built into the back cushion of the seat and can be inflated or deflated by operating a small air pump also fitted into the seat and controlled by a lever on the side of the seat.
Bostrom will keep on selling its mechanically sprung seats alongside the air suspension model which really represents the state-of-the-art (or state-ofthe-science) in suspension seats.
Seat_design is a science and has become increasingly important over the past few years as driver comfort has moved up the list of priorities of many vehicle manufacturers and operators.
A recent report by the Battelle Institute of West Germany (CM„ March 7) highlighted the many pressures a modern longdistance lorry is under and likened his status to that of a deckhand, but with the responsibilities of a commander. Bostram believes he should have the comfort of a commander's cabin.
It is difficult to disagree.