Since introduction of the widely- used B-double combination some three decades ago, truck manufacturers have been tailoring specific variants of their heavy-duty prime movers for the task of hauling these combinations that can achieve gross weights of up to 68.5 tonnes under Performance-Based Standards (PBS).
Over recent years the horsepower ratings of B-double prime movers have gradually crept northwards from the 500hp standard that for many years was considered adequate, with 550 to 580hp ratings now widely accepted as ideal for the task.
These ratings seem to strike just the right balance between power and fuel efficiency – an ever-important factor in linehaul applications where even a fraction of a percent improvement in fuel economy adds up to a substantial saving over time.
Manufactured in Germany, MAN trucks are offered to the Australian market by Penske Commercial Vehicles which also sells the North American-built Western Star brand.
This is a common theme among the major truck suppliers to cover the varying requirements and tastes of Australian heavy-duty truck operators, some of whom prefer North American and others European brands.
At the heart of MAN’s TGX 26.580 model is the proprietary D38 15.2 litre engine developing 580hp (427kW) at 1,800rpm and a robust 2,900Nm (2,140lbft) of torque between 930 and 1,350rpm.
The same engine is also used in the TGX 26.640 where it is tuned to deliver 640hp (471kW) and torque of 3,000Nm (2,212lbft) at the same respective rpm. This model is aimed squarely at road train roles with gross combination masses (GCM) of up to 120 tonnes.
The engine features twin turbos and achieves Euro 6 emissions status using a combination of selective catalytic reduction (SCR), a CRT particulate trap and low temperature exhaust gas recirculation (EGR).
Engine braking comes courtesy of MAN’s five-stage Turbo-EVBec electronically controlled engine brake providing a maximum retardation of 630kW (840hp) at 2,400rpm. The company says the system maintains constant braking output as heat is dissipated via the exhaust gas stream.
Engine power feeds into a ZF TraXon 12-speed overdrive automated manual transmission (AMT) via a 430mm diameter single-plate MFZ clutch.
Known as TipMatic in MAN-speak, the cutting-edge unit features a twin-countershaft constant-mesh configuration with electro-pneumatic clutch and gearshift actuation. It features a first gear ratio of 12.92:1 and an overdrive of 0.77:1.
It has normal automated and manual modes to allow the driver to manually select gears when necessary and a manoeuvring mode for precise low speed operation in either forward or reverse. Another useful feature when negotiating heavy traffic conditions is called Idle Speed Driving. This allows the vehicle to smoothly creep forward without accelerator pedal input when the service brakes are released.
Moving rearward, the 13-tonne rated tandem drive assembly includes four-bag electronically controlled air suspension with the rear axles featuring sealed-for-life hubs, diff locks and a final drive ratio of 3.36:1.
Meanwhile, the nine-tonne rated steer axle also includes sealed-for-life hub units and eight-tonne capacity parabolic leaf springs with shock absorbers and a stabiliser bar.
The heavy-duty specifications continue through to the chassis, which is a ladder frame construction utilising high strength steel C-section members measuring 270 x 85 x 8mm.
Attached to the chassis are square section aluminium fuel tanks with capacities of 620 and 460 litres, mounted on the near and off sides respectively, as well as an 85-litre nearside-mounted Adblue tank.
Having a wheelbase of 3.3 metres, the prime mover sports a compact kerb-to-kerb turning circle of 16.4 metres and in XLX cab trim tips the scales at 9,230kg – 5,445kg over the steer and 3,785kg on the drive.
Conversely, the XXL cab version tares at 9,435kg with respective steer and drive axle weights of 5,505 and 3,930kg.
Somewhat unusually for a new Euro 6 compliant European prime mover, this unit with the XLX cab comes standard with a vertical exhaust while the taller XXL cab variant has the option of either vertical or horizontal exhaust.
As for internal dimensions, the XLX cab has a floor-to-roof height of 1,820mm along with width and length of 2,440 and 2,280mm respectively. The XXL cab has identical width and length measurements, while its height is 2,030mm.
In keeping with other prime movers of its ilk, the MAN is well endowed with a comprehensive suite of safety equipment including EBS and ABS mastered disc brakes on all three axles. The brakes also have electronic wear monitoring and wear equalisation functions.
Also featured are electronic stability program (ESP), anti-spin regulator (ASR), roll-over protection (ROP), emergency brake assist (EBA2), lane guard system (LGS) and MAN’s ‘Easy Start’ (hill hold) function.
Over the hill
Our test drive started from Penske Commercial Vehicles’ head office on the western outskirts of Brisbane, with the B-double loaded to a GCM of nearly 62 tonnes.
The route was planned to take in the considerable climb of the Great Dividing Range through Cunningham’s Gap west of Brisbane; then out towards Warwick before turning north to Toowoomba and descending the Range back to base. Both the ascent and descent are as tough as they come for testing a fully loaded B-double.
Aiding in the pre-trip check is the useful feature whereby all the exterior light functions can be cycled through by the driver at the press of a button.
It was easy to settle into the ISRI air-suspended drivers chair with integrated seatbelt, armrests both sides and multiple adjustments for lumbar support. Similarly, the large diameter steering wheel is adjustable for rake and reach, making it easy to find the ideal position for comfortable long-distance driving.
The dash is neat and functional with all controls within easy reach of the driver. Two large circular dials for speedo and tacho sit above four smaller ones for air pressures, engine temp and fuel level. In between is a multitude of warning lights that blaze like a Christmas tree when the ignition is activated.
To the immediate left is a seven-inch colour touch-screen infotainment system with steering wheel mounted controls.
Below this are two generously sized slide-out document drawers and beneath the bed resides a 42-litre slide-out refrigerator.
The mattress width is 820mm and an additional bunk folds down from the rear wall.
After resetting the trip information to enable an accurate fuel consumption reading at the end of the trip, we were on our way.
Employing a 12-speed transmission means the gap between each ratio is higher compared to 16- or 18-speed units. Nevertheless, prodigious torque output from 930rpm endows the MAN with relatively good acceleration as it tops the 1,800rpm mark before upshifting, whereupon engine speed subsides to around 1,300rpm, which is also the cruise rpm at 100km/h in overdrive top gear.
At this speed the interior noise level is supremely subdued and consists mostly of a very low and muted note from the engine along with a miniscule amount of wind noise. In other words, it’s pretty quiet.
The ride inside the four-point air suspended cab is also extremely smooth, particularly impressive considering we are travelling along the notoriously lumpy Cunningham Highway.
Upon reaching the foot of the climb to Cunningham’s Gap, the MAN allows revs to fall to 1,000rpm before skip-shifting twice, then after a single shift to seventh gear it settles into the pull, holding steady at 35km/h and 1,500rpm.
Once over the crest, and with the engine brake set on the third of five stages, a well-controlled descent with no service brake intervention was reassuring.
The next stage to Toowoomba over undulating terrain was done with ease, with the precise steering making it child’s play to keep the unit positioned ideally on the road.
Then there was the very steep and long descent of the Range from Toowoomba that was accomplished in sixth gear with the engine brake once again giving a powerful account of itself set on the fourth stage.
As for fuel economy, over the trip of 310km of challenging terrain and with fuel conscious driving techniques employed, the average fuel consumption readout showed 1.72km/l (4.85mpg) – a solid effort considering the high gross weight and prevalence of hills enroute.
All up, we came away very impressed with the overall package of this prime mover. It feels solid and well-built with a superbly comfortable cab and an array of appointments that work together to minimise driver fatigue during the long hauls.
With a strong performing and seemingly bullet-proof engine complete with electronic monitoring that determines the optimum service intervals, there’s every reason to believe a linehaul service life of at least one-million kilometres would be comfortably achieved.