What comes around, goes around, and Scania Australia is once again pushing the virtues of the single-drive 6×2 configuration for some applications where tandem-drives have long been the norm. This time ‘round though, Scania has time and technology to draw on. PAUL MATTHEI reports after jockeying a G440 6×2 on a short run out of Melbourne.
The ‘Lazy’ Option
While trucking applications like construction, quarrying, logging and other off-road ventures obviously require the superior traction afforded by the tandem-drive 6×4 arrangement, Scania suggests there’s no valid reason why 6×2 prime movers can’t operate just as effectively as their double-diff siblings in specific highway roles.
And after the smooth, untroubled performance of just such a unit on a 185 km loop north of Melbourne, it’s difficult to disagree.
But why would you choose to operate a 6×2 prime mover when the ‘traditional’ 6×4 configuration has been the mainstay of Australia’s heavy-duty truck fleet since Adam was a boy?
Quite simply, it all comes down to two words: Saving money! Measured against an equivalent 6×4 unit, a 6×2 prime mover in the right application can provide quantifiable savings by a number of means and for its part, Scania Australia cites the following benefits:
• Greater payload potential due to reduced tare mass;
• Meaningful fuel benefits and reduced carbon footprint;
• Lower capital investment as a result of fewer mechanical parts; and
• Reduced servicing and repair costs.
Expanding on each point, Scania says its 6×2 G440 prime mover fitted with the two-pedal (fully automated) Opticruise transmission tares around 400 kg lighter than its 6×4 equivalent. In this case, it doesn’t take a rocket scientist to figure that, all other things being equal, an additional 400 kg of payload can be legally carried by the 6×2 unit.
Then there’s the fuel saving which actually amounts to more than what’s gained by simply having 400 kg less tare weight to haul. That’s because there’s no frictional losses associated with powering a second drive axle and through shaft. Furthering this benefit, Scania specifies its 6×2 arrangement with a direct drive gearbox rather than an overdrive unit which initially sounds counter intuitive given the overdrive’s inherent ability to reduce engine speed and therefore fuel usage at highway speeds.
However, it actually takes slightly less engine power to propel a vehicle through a direct (1:1) top ratio than an overdrive ratio because the latter involves the power being delivered via the countershaft rather than directly along the main shaft of the transmission. All up, Scania says it amounts to a further one percent fuel saving.
Anyway, the 6×2 unit comes standard with an ultra tall 2.71 rear axle ratio which effectively compensates for the lack of an overdrive top gear and according to Scania’s calculations, actually delivers an identical final drive ratio to that of a 6×4 equivalent with its 3.42 rear axle and overdrive top gear. Importantly, to cater for low speed manoeuvring, the 6×2 unit features a stump pulling 16.3:1 ‘crawler’ gear.
Again according to Scania, local testing has shown the G440 6×2 has the potential to achieve up to 12.5 percent better fuel economy and at 100 km/h has an additional 10 hp at the drive wheels compared to its ‘double diff’ equivalent.
Continuing the credits, one less diff and no through shaft also mean a lower purchase price and less maintenance and repair costs over the life of the vehicle. In fact, Scania says savings in regular servicing costs could amount to almost $1000 per year for a vehicle travelling 200,000 km annually, while 6×2 vehicles running within a Scania repair and maintenance contract would cost less per month than a Scania 6×4 on a similar contract. It’s also worth mentioning the lower tyre wear rate of the lazy axle and the fact that it can be fitted with steer tread pattern tyres which in most applications tend to have slower wear rates than chunkier drive treads.
These days, all Scania 6×2 prime movers are also equipped with traction control, differential lock and load transfer – a system which engages at speeds below 30 km/h to vary air pressure between the lazy and drive airbags and thus add more weight over the drive axle – to maximise traction in conditions likely to be encountered during typical operation.
Scania Australia organised a test drive of a G440 6×2 running from its Campbellfield (Melbourne) headquarters, north along the old Hume Highway to Seymour before turning to join the ‘new’ Hume freeway on the return run. Sure, it wasn’t far – just 185 km – but I’d never driven a 6×2 prime mover before and was eager to find out if there would be any discernible difference in driving terms compared to an equivalent 6×4 unit.
My curiosity was soon satisfied and the short answer is that it was impossible to tell the difference. Quite simply, the G440 6×2 grossing around 38 tonnes did the job with the same quiet efficiency we’ve come to expect from each and every model in the current Scania line-up.
And on that point, Scania says it plans to offer the 6×2 option across its entire range comprising P, G and R-series cabs with either five, six or eight cylinder engines. Meanwhile, with the G 440 6×2 already available, Scania says a number of units have been trialled by a variety of Australian transport operators with most reporting exceptional driver acceptance of the new configuration.
Back to the drive though, a revealing part of the exercise centred around the use of Scania Driver Support (SDS), an inbuilt system that helps the driver modify driving style in order to maximise fuel efficiency. Indeed, the drive program typified something of a two pronged attack on fuel usage, given the 6×2 configuration and driving style are both major influences.
SDS works by awarding a star rating of between one and five stars depending on how well the driver anticipates road conditions and uses the vehicle’s momentum to maximise fuel efficiency and minimise brake use. The star rating appears periodically on the instrument panel display along with the driver’s cumulative fuel efficiency score (expressed as a percentage) for the entire trip.
For example, my initial fuel efficiency score according to the SDS system was a fair 66 percent but with Scania driver trainer Alan McDonald suggesting I back off the throttle just before the crest of each hill and allow the vehicle’s momentum to do more of the work on the downhill run, my score had improved by 10 percent at the end of the trip.
Back at Campbellfield, the truck’s on-board trip computer revealed a consumption rate of 2.65 km/ litre (7.49 mpg) which, all things taken into account, was an impressive result and certainly endorsed the fuel saving potential of the single-drive 6×2 configuration.
All up, it seems there is nothing but positives for the 6×2 set-up. However, one aspect which didn’t rate a mention in Scania’s presentation is resale value. Historically, secondhand three-axle prime movers with just one drive axle are about as popular as a burqa in a bank. Obviously this point would need to be taken into account when calculating whole-of-life costing on a 6×2 vehicle, and there’s no doubt finance companies would factor lower residual values (compared to 6×4 units) into their leasing arrangements.
That said though, if the price of a new 6×2 is substantially cheaper than its 6×4 equivalent, then perhaps the reduced resale value is offset to some extent.