Heavy responsibility for lightweight range
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With a new cab, chassis frame and front axle, the Roadrunner is poised to attack the burgeoning 7.5-tonne market. Tim Blakemore applauds Leyland's clever cab design
THE BAREST FACTS of the matter are these. Leyland has replaced its range of six to 10tonne-gvw vehicles with one which has a new cab, a new chassis frame and a new front axle, and which is available at three gross vehicle weights (6.2, 7.5 and 10 tonnes), with four wheelbase options. However, there is a great deal more to the Roadrunner story than that.
Is there ever a clear-cut answer to the question: when did development work on any new commercial vehicle begin? Product planners consider options over a period of time before any commitment is made, with the result that some "development" is always done before any project gets the official green light. So it was with Roadrunner.
But however you measure it, the time taken by Leyland's engineers to bring this new model from the drawing board (actually the visual display unit) to the showroom was short.
While the MT211 project, as it was coded before the model name was coined, began shortly after Leyland's "Radical Plan" of 1981 — the major effect of which was to split the company into seven separate business units — programme approval and commitment to production did not occur until March 1982.
Leyland management was understandably keen to get its new lightweight on the road as quickly as possible. Its share of the six to 10-tonne market sector has been tumbling for some time, particularly at 7.5 tonnes gross vehicle weight, and since 1976 this maximum non-hgv weight has become so popular that more commercial vehicles are registered at this weight than at any other.
The 15-year-old Terrier just could not seriously compete against its modern rivals, notably Ford's Cargo, which was introduced in March 1981 and which has won an extraordinary market leadership at 7.5 tonnes gvw. This year, for example, up to the end of August, Ford's share of UK registrations at this weight stood at over 41 per cent, while Leyland's was less than 10.
That is why speed of development of Roadrunner was necessary, but how was it achieved?
The answer to that lies mainly at Leyland's technical centre at Moss Side, which, when it was officially opened in October 1980 by the then Industry Secretary Sir Keith Joseph, was described by him as "a hub of excellence."
The Roadrunner is the first Leyland vehicle to be fully developed at the Moss Side tedhnical centre and its sophisticated, computer controlled electro-hydraulic test rigs helped greatly in accelerating the test programme.
Peter Capon, Leyland's Vehicles' product development director, gave me one specific example of time saving which the new test rigs at Moss Side had made possible. "Pave' testing of a new vehicle normally takes six to seven weeks because various failures occur which have not become evident during component testing," he said. "Roadrunner's pave' testing was completed in less than three weeks, so successful was our rig testing of components."
Only two problems were revealed by the whole-vehicle pave' testing and both were easy to solve. One was a weakness in a spring hanger-bracket pressing and one was a resonance from the foundation brakes.
Remarkably, the entirely new cab suffered no failures at all during the pave' testing.
That must be mainly a result of its exceptional small number of panels and therefore small number of joints and potential failure points. Leyland's engineers used computer-aided design techniques more extensively on the Roadrunner cab and chassis frame than they have for any other previous model. Clearly that, too, has paid dividends in saved testing and rectification time.
The C44 cab
APART from its visual impact, the Roadrunner cab is undoubtedly the most significant part of this new vehicle story. Cab development certainly swallowed the lion's share of the MT211 project's budget and given the parlous state of Leyland's finances over recent years it is not difficult to understand why the BL board thought long and hard before approving that expenditure on tooling for a new cab.
Less expensive options that were seriously considered included widening the Freight Rover Sherpa MT210 cab to suit the heavier vehicles (that proposal, which many Leyland engineers still flinch at the thought of, came came close to reality and would have been the C43 cab), and scaling down the C40 cabs used on heavier Leyland vehicles. A casual observer could be forgiven for thinking that the C44 cab is a scaled down version of the C40 component, but that it definitely is not.
The similarities in styling are deliberate, and not at all surprising, since Ogle was styling consultant on both projects and understandably Leyland wants all its trucks to be identifiably Leyland. At this stage it is worthwhile explaining the relationship between Leyland, Ogle and Motor Panels (Coventry) in the production of the C44 cab, because it has tended to become blurred so far as C40 is concerned.
The Motor Panels involvement in the new cab is an assembly-only function. The panels are pressed in West Germany and the Republic of Ireland with Leyland's own tools and then transported to Coventry for assembly.
The cab shells are then taken to Leyland's assembly hall at Preston where all the other T45 vehicles are assembled.
A Leyland team of engineers under Bill Lowe, chief engineer, components, is fully responsible for the cab design. Ogle's contribution was to provide the "aesthetic styling".
The full story of the C44 cab design warrants a separate description, but it is worth em phasising here its most important features. Foremost among those is the substantial reduction in the number of pressings used in it compared to the Terrier's G cab or indeed compared to any other commercial vehicle cab of this size.
It is illuminating to compare the parts count on the Roadrunner cab with that of the Ford Cargo, for instance, a modern rival which was also designed for ease of assembly and low weight. Cargo has 171 cab parts not including trim whereas Roadrunner has only 68.
This big difference stems from the difference in the cab structures -Cargo has a conventional underbody box frame on which its sheet steel panels are mounted. The C44 cab has no such subframe. In Bill Lowe's words "the principle has been to make every panel work" (as a load bearer) and computeraided finite element analysis has enabled him to achieve this.
Fewer parts help to save weight, but, while unladen weight saving (particularly over the front axle) was recognised as an important consideration, the real motivation for this quite radical change of design was a reduction in manufacturing cost.
It is difficult to obtain precise figures, but it is reckoned that the tooling cost for a new commercial vehicle cab of conventional design will be of the order of £5 million. By dramatically reducing the number of pressings used Leyland has probably halved that cost and the savings continue into the assembly process.
Compared to the Terrier's cab the C44 has 40 per cent fewer spot welds, the time needed for cab assembly has been reduced by 60 per cent; press shop man/minutes have been reduced by 50 per cent; and the number of welding guns used has been reduced by 75 per cent.
Operating engineers may be impressed with this manufacturing efficiency but many will be more concerned with the practicalities of repairing the Roadrunner cab. As a result of its monocoque design, will it cost a fortune to repair after an accident?
Bill Lowe insists not and the British Insurance Association's well respected Motor Insurance Association's well respected Motor Insurance Repair Research Centre at Thatcham confirm s, after studying the Roadrunner cab, and indeed having been involved at the design stage. Future work planned at Thatcham includes impact testing the C44 and other cv cabs and CM will report on thii, in due course.
Chassis frame
ROADRUNNER'S chassis frame is new, not a modified Terrier component, but is of conventional design. Its steel is hightensile, 29 ton/sqin yield stress, and the same frame with riveted cross-members is used for all models, tippers included, from six to 10 tonnes.
The chassis side-members, measuring 192x65x 4.5mm, are straight, parallel and flat topped. They are pre-drilled for bodymounting brackets but these are not supplied as standard — they are an option.
The shackled, tapered leafspring suspension with very long springs has telescopic dampers front and rear. An optional heavy-duty suspension offered for tipper models uses the same springs that are employed as standard for the 10 tonnes gvw haulage model. A high centre of gravity kit with anti-roll bars is not at present available for Roadrunner but is likely to follow soon.
Engines
IT IS PRACTICALLY certain that the six-cylinder 98-Series, Bathgate-built engine which at present powers Roadrunner will only do so up to 1986, which is when the Bathgate plant is due to be closed.
It has been widely expected that the engine to replace the 98-Series two years from now will be the Cummins/Case sixlitre, the B-Series, which until a last-minute change of plan, Leyland was going to assemble at Bathgate. But now it is not certain that Leyland will buy this engine. Certainly no supply contract has yet been signed.
Leyland's official position is that it is negotiating for the supply of an engine to replace the 98-Series and it is clear that a four-cylinder turbocharged BSeries is being given serious consideration.
But is seems other engines are in the running and one of these may surprise us.
Whichever engine is eventually chosen, it will be hard put to match the current 98-Series standards of reliability. As explained in CM, November 5, 1983, Leyland has taken steps to solve what was a serious, reliability problem with this engine and reports we receive suggest that they have been effective.
So dependable has it become that many operators may now mourn its demise. But from a manufacturer's point of view, the 98-Series is unable to meet current and future requirements in a number of areas, particularly in weight and noise.
The trend towards higher horsepower in the Roadrunner's wpm category is also tending to leave the 98-Series behind.
Leyland's engineers gave serious consideration during the new vehicle development to fitting a four-cylinder 98-Series, as used in Terrier, which would have helped in keeping the front-end weight down, but rejected the idea because the normally aspirated version is not powerful enough and the turbocharged version has insufficient low speed torque.
Two horsepower settings are offered for the Roadrunner, 68kW (91hp) and 81kW (109hp) net installed to the BSAU 141a standard, at 2,600rpm.
The higher-powered engine's maximum torque of 355Nm (262 Ibft) is developed at 1,650rpm, while the lower-powered version's 311Nm (230 lbft) is developed at 1,400rpm.
Transmission
THE FIVE-SPEED synchromesh T5-200 Turner gearbox used in Terrier has been extensively reworked by Spicer Transmissions for the new vehicle and is now designated T5-250. The box's weight has been reduced by the use of a cast aluminium casing and its torque capacity increased by widening the gear teeth by about 10 per cent.
A major objective in the redisign was to lower gearshift loads and geerally improve gearshift quality. This has been achieved by moving from a single-rail to a three-rail selector system and the gear selector turret is now offset from centre.
Leyland reckons that with a warm gearbox the amount of effort required at the gear lever for shifts to first and second gears should be only about 4kg (91b) while even in the worst case of a cold gearbox and low gear selection that effort should never exceed 14kg (301b).
In a short drive of a fully laden 8.12 Roadrunner, one of the features that impressed me most was the gearshift quality — always precise and never requiring much effort. Clearly, that is important for a vehicle which will spend a lot of its time in urban areas.
Leyland's reasons for choosing the Spicer gearbox in preference to the ZF S6-36 model which, since it was used in Freighter was an obvious candi date, were "purely commercial".
Spicer is also supplying the Roadrunner propeller shaft, 1480-Series, two-piece, and flangeless, and this is one of the first vehicles to be fitted with its new half-round, end-yoke design.
The only significant change made to the Bathgate-built Terrier rear-axle for Roadrunner is that a new ratio of 4.36:1 has been introduced. This takes maximum geared speed up to 103km/h /64mph) — that's still less than the new 70mph legal motorway limit for 7.5-tonners but it was chosen mainly in the interest of keeping engine speeds down. The alternative ratios for Roadrunner's spiral bevel differential are 4.71 and 5.125:1, which give maximum geared speeds of respectively 59 and 54mph.
Wheelbase and body lengths
THERE ARE THREE design weights, 6, 7.5 and 10 tonnes, in the Roadrunner range, with the lower-powered engine offered as an option on the two lighter models, but it is evident that the 7.5-tonner will be produced in by far the largest numbers and wheelbase and body lengths have been designed to suit this weight category.
The 8.10 and 8.12, 7.5-tonnegvw Roadrunner models have plated front and rear axle weights of 2,800kg and 5,250kg, more in each case than Terrier offered and enough to give fairly generous latitude for unevenly distributed loads.
A factor which Leyland's engineers kept very much in mind in the design of Roadrunner is that 7.5-tonners will often be unloaded from the rear, pushing the c of g forward and tending to overload the front axle.
Another factor high on their list of objectives was to gain good manoeuvrability and this they achieved in no small measure. The largest wheelbase, 4.4m, model will accept a nominal body length of 6.2m (20.3ft) yet its quoted kerb to kerb turning circle is only 14.7m (48.2ft).
However, a driver would not need a tape measure to recognise how good is Roadrunner's manoeuvrability. It is one of the features which, like the comfort of the seat, the roominess of the cab, and the wide field of vision, impress after only a short time behind its wheel.