KEY REQUIREMENTS FOR A HEAVY HAULAGE TRACTOR UNIT ARE HIGH LEVELS OF ENGINE POWER AND TORQUE, COMBINED WITH AN EFFECTIVE TRANSMISSION. BOB BEECH GOES ON THE ROAD WITH THE LATEST TO ENTER SERVICE IN THE UK – THE NEW SCANIA R730 8X4 TRACTOR UNIT – MOVING A HITACHI ZAXIS 870 EXCAVATOR WITH THE WALTERS GROUP.
Engine outputs have risen steadily over the last four decades. Back in the 70s, a 300–350bhp engine was considered massive. Thought suitable only for long-distance international hauliers, and specialist heavy transport companies looking for alternatives to the relatively low-powered offerings available from most British truck makers. Two manufacturers led this trend more than any others. For over 40 years the Swedish duo of Volvo and Scania have striven to outdo each other in the power stakes; the battle shows little sign of ending just yet. Both have repeatedly claimed to not be engaged in a power race. But it looks very much like one from where we are sitting, and (to be honest) let it continue: they both have built some tremendous vehicles which have served operators very well, especially in heavy haulage.
Whilst arch-rivals Volvo hold the top-power crown at present, with the FH16/750 – which has 20bhp and 50 Nm more than Scania – the R730’s 3500Nm is still way ahead of other European competitors. MAN’s new D38 engine is rated at 640bhp, the Mercedes OM473 at 630bhp, with 3000Nm torque output each. Yet power alone is not enough when shifting heavy loads. Transmission plays a vital role. Mercedes combines an automated two-pedal gearbox with the much praised Turbo clutch (TRC), which double functions as a fluid coupling – for starting from rest – and as a powerful primary retarder. MAN use an automated gearbox, combined with a conventional torque converter, which once again is used for starting and low-speed manoeuvring. Volvo and Scania have taken a different approach with their most powerful engines and specified, modified versions of automated manual transmissions. But there are differences. The Volvo I-shift is a 12 speed two-pedal with specialist software.