• It had to happen. Ever since HGV speed limits
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were changed back in March 1984, Commercial Motor has watched the increasing demand for more powerful 7.5tonners with a fair amount of scepticism. It's got nothing to do with whether or not a 7. 5-tanner should be allowed to travel at 1131(m/h on the motorway (that's a separate matter altogether). It's simply a matter of economics.
During the past four years we have taken no fewer than 17 7.5-tonne trucks around our tough Welsh middle-weight test route, which includes a 130km fuelguzzling dash down the M4. Of the contenders fitted with engines pushing out more than 97kW (130hp), not one has managed to return more than 17.7 litres/ 1001cm (16mpg).
We have been forced to conclude that while the ever-growing number of highpowered chassis sold in Britain are more than capable of providing fast journey times, the price of that performance, at least in terms of fuel consumption, is too high. Having taken this stance it was inevitable that sooner or later a manufacturer would offer us a 7.5-tanner which would buck that trend.
• FUEL CONSUMPTION
The vehicle in question is the Cumminspowered Leyland Daf Roadrunner 8.15.
Not only has it finally broken the 16mpg (17.7 litres/100km) barrier with its overall consumption of 17.48 litres/100km (16.16mpg), but its average speed of 74km/h around our Welsh route also makes it the second fastest 7.5-tonner we have ever tested.
What makes the 8.15's performance even more impressive is the fact that it achieved these figures not with a dropside or tipping body (as is usual on 7.5-tonners supplied to us for test) but with a fullheight dry freight box body. A handful of 7.5-tonners with low bodywork have come close to the 8.15 on fuel economy its lower-powered brother,the Roadrunner 8.13 managed 17.5 litres/100km but no other box-bodied contender has even come close.
The most recent high-bodied model, tested by Commercial Motor was the 0813 Iveco Ford Cargo curtainsider which could only manage 19.8 litres/100km (14.3mpg).
Before any operator reaches for his cheque book, however, it is important to recognise exactly where the 8.15 Roadrunner is at its most fuel efficient. Its 19.8 litres/100km, achieved on the M4 section between Chievely and Aust services, was helped by a build-up of traffic and bad weather, which kept us below the maximum speed limit for some of the way. Using Leyland Dafs own TOPEC computerised vehicle performance predictions, fuel consumption for the 8.15 will certainly deteriorate if a steady 113Icrn/h is held for an extended period on the motorway.
Where the 8.15 does score, however, is on slower A-roads, when the Cummins' revs fall back to more fuel-efficient levels, fulfilling the "big engine working lazy" legend. This was certainly the case with our 8.15, which completed the slower A and B-road section at a much improved 16.23 litres/100Icm (17.4mpg).
The message is clear. Keep a boxbodied 8.15 at 1131cm/h all day and you'll probably end up with no more than 23 litres/100Ln (12mpg) but mix it with A-road running, and it will claw back more-than-adequate fuel consumption.
• DRIVELINE
Its almost two years since Leyland dropped the Roadrunner's old Bathgate-built 98-series engine, in favour of the Cummings B Series. Under the pre-Leyland Daf regime, the B Series was to be built at Bathgate, but that fell through. The
5.88-litre straight-six Cummins engine is badged in the Roadrunner as the Leyland 300-series, but don't be fooled. It may have a 300-Series label on the block (put there no doubt as a marketing exercise),, but underneath it there beats a, Darlington-built B Series.
Three versions of the 300-Series are used in the Roadrunner. These are the naturally-aspirated 301 and 302 engines (used respectively in the 8.12 and 8.13 chassis), and the turbocharged 310 engine, which has been available since last September. They all drive through the same Borg and Beck clutch, Turner T5290 overdrive-top five-speed gearbox and Leyland back axle.
Leyland Dars policy of using the last two digits in its model designations to refer to nominal horsepower is somewhat misleading as it refers to gross, rather than nett outputs. In the Roadrunner 8.15, for example, the 310 engine may have a gross output of 145hp (108kW), but when installed this falls back to 138hp (103kW). This is in marked contrast to Renault's S08-150 Midliner which, as its badge suggests, has a nett output of 154hp (113kW). The 8.15 then may not be a true 150hp (112kW) chassis despite the promise of its badge, but there can be no doubt that it has power aplenty on tap.
Accelerating from a standing start up to 80km/h, it leaves the 0813 Cargo curtainsider for dead, stopping the clock a full 12 seconds before it. The only 7.5-tonners we have tested that can keep up with it are the 814 Mercedes and the nowsuperceded MAN 8.136F — and once again their best figures were achieved with dropside, rather than box bodies.
• PERFORMANCE
The most impressive aspect of the Roadrunner's power, however, can be found when accelerating between 64-96km/h. Put your foot down to the floor and the 8,15 pulls and pulls and pulls with hardly a murmur from the Cummins engine, which seems quiet enough to satisfy even the most irritable librarian.
This mid-range power is especially reassuring when overtaking long vehicles on single-carriageway roads, removing the "will it or won't it?" element of the manoeuvre. It is available torque, rather than just brute power, that separates the 8.15 from its rivals. Its 449Nm (3311bft), delivered between 1,410 and 1,970rpm, is bettered only by the Renault Midliner and the most powerful 0815 Cargo, while the latest MAN 8.150F's 450Nm is so close as to make no difference.
The 8.15's high, and highly usable, torque clearly contributed to its excellent hill performance. It stormed up the snaking 14% gradient outside Wantage in two minutes dead, well ahead of any of its rivals.
All this makes for an extremely lazy drive, although anyone used to handling a big truck will have to forget all about letting the engine lug down. The 300/B Series' revs have to be kept up fairly high in order to get the best in fuel economy and power, especially as maximum power is delivered at 2,600rpm, while peak torque comes in at 1,600rpm.
Surprisingly, Leyland Daf does not offer a rev counter on the 8.15 which is a pity, as it would certainly help a driver get the best from the B Series. In its absence gear changes have to be based on roadil speed. This works out fairly well withMl changes from second to third taken at 321(m/h, third to fourth at 481(rn/h and from fourth to fifth at 641(m/h. When changing up on a gradient, however, the lower gears need to be held longer, and road speeds allowed to build up higher in order to keep the B Series' revs at the right level after the upshift. Nonetheless the 8.15 will lug down to below 641(m/h in top — but not for too long. In general it is better to change early, rather than late.
On level ground the 8.15 can pull away in second without having to cane the clutch too hard, which is probably just as well, as selecting first on the noticeably notchy Turner box requires some effort. In common with other five-speed 7.5tonners we have tested there are also gaps between the ratios in the Roadrunner's gearbox, particularly between third and fourth, but fortunately these tend to be masked by its raw power.
• CAB COMFORT
The standard Roadrunner interior is best described as "fleet practical" rather than luxurious. This was no doubt in Leyland Dots corporate mind when it conceived the optional QX trim package for the Roadrunner which, among other things, includes fitted carpets over the standard rubber floor covering, rear window curtains, storage nets on the rear bulkhead, a Philips 550 radio-cassette player and an lsringhausen air-suspended driver's seat.
The dark red carpet, combined with the matching cloth-trimmed seats and lightgrey door and roof trim, makes the QX Roadrunner interior extremely attractive, and one that will certainly appeal to smallfleet operators and owner-drivers.
The only niggling aspect of the interior package on our 8.15 was the poor fitting of the carpet around the Roadrunner's unique kerbside window: it was simply cut off at the base of the glass, leaving an unfinished edge, The Roadrunner dash is easy to read, although colour-coding the gauges would make it even better. Few drivers, however, will find fault in its well laid out cockpit where all the controls are within reach.
The Roadrunner is still one of the easiest trucks to get in and out of, while cross-cab access is a breeze. Visibility from the driver's seat is above average although apart from offending the original stylists, why must Leyland Daf still fit unequal size mirrors on its trucks?
Getting to grips with the 8.15's engine will not present any problems. After releasing the locknut sited on the nearside of the bench seat, and pulling the release toggle, the cab can be raised manually. All major service items are within easy reach while daily driver checks are sensibly located at the nearside behind the cab.
• HANDLING
On the road the 8.15's ZF power steering is precise but it takes a while to get used to due to its lightness. It is, however, notic,ably affected by ruts on the motorway worn by wider-tracked HGVs, although there is not much you can do about this. On the plus side the 3.65mwheelbase 8.15's tight turning circle will certainly be appreciated by delivery drivers in cramped conditions.
While the overall ride on the Roadrunner is comfortable, if somewhat soft, it can be a little bouncy at times over poor road surfaces. This was not made any easier by the Isringhausen air-suspended driver's seat which needed a stronger damper. In the end, after a particularly lively session over a switchback A-road, we locked the seat up and kept it that way throughout the rest of the test. Offering a suspension seat may be a useful selling point, but in reality the 8.15's suspension is good enough to make it superfluous.
When the Roadrunner gained the Cummins B Series, it was also treated to front disc brakes. The combined front disc/rear drum, air/hydraulic system is undoubtedly effective, but it lacks progression. The 8,15 driver has to learn to brake smoothly or run the risk of being plastered against the windscreen. This full-off/full-on style of braking is by no means unique to the Roadrunner among 7.5-tonners, but that does not make it any the more welcome.
• SUMMARY
Just as there is a growing demand for more power at 38 tonnes, there is a similar call for higher engine outputs at 7.5 tonnes. Yet how much of this is manufacturer rather than customer led? Many transport operators currently demanding 97kW-plus in their 7.5-tonners simply don't need the extra power — and they would be better off financially sticking with a lower-rated model.
Times are changing, however, and hauliers are increasingly using 7.5-tonners for long-distance motorway work. With high-profile bodywork a more powerful engine is needed to maintain reasonable average speeds — but there is a price to be paid in fuel economy.
Leyland Dafs 8.15 Roadrunner certainly has the power, and as long as it is driven sensibly, and is fitted with aerodynamic aids, it can more than cover its costs at the pump. For "sensible" read keeping the Cummins engine at the right revs, and being prepared to settle for 105Iuri/h, rather than 113krn/h on the motorway. Did somebody say speed limiter?
If the Roadrunner was a good truck to start with, the arrival of the turbocharged Cummins B Series and the QX trim package makes it one of the most attractive versions to date. In the right hands it could prove to be the vehicle that finally eases Iveco Ford's stranglehold on the 7.5-tonne market.
0 by Brian Weatherley