Tractive force 05 April 2016

Specifying tractors should be a science, not an art – starting with a frank analysis of the application. Brian Tinham reviews considerations in light of recent truck developments

Some things don’t change: fuel efficiency is still king for the vast majority of operators running tractors on general haulage. Fact. However, that measure of performance is not the only one. For some it may share the top slot with the combination’s potential payload and/or flexibility (hence in part the popularity of 6x2s).

For others, it may be manoeuvrability or performance, particularly where operations involve timed deliveries. Or even cab size, equipment and trim, given today’s driver recruitment and retention challenges. And no one can afford to ignore package price and RV (residual value): financial considerations frequently trump technical merit.

That’s a lot of parameters. So whatever matters to you, if you haven’t specified tractors in the last 12—18 months, it shouldn’t be surprising that what’s available has changed. Quite simply, today’s Euro 6 tractors optimised for your operation may well share little with the configuration you chose for yesterday’s Euro 5. And note: in that timeframe most Euro 6 units have moved on too.

What’s new? Well, it’s not just about the choice of Euro 6 engine emissions management, important though that may be. Nor is it only the growing numbers of downsized engines (mostly nine and 11 litre) claiming improved kpl, dependent on application. Nor even the fact that, across the board, peak torque is increasingly delivered some 100rpm lower in the band – meaning it’s time to revisit preferred power, transmission software and axle ratios.

All these need consideration, but so do newer chassis and driveline variants, intelligent AMTs (automated manual transmissions), smarter telematics packages and, of course, the latest generations of tyres. We might also list: better safety systems (and not just the now mandatory AEBS emergency brake assist and lane departure warning systems); and small mid-lifts – hitherto the preserve of bulk carriers but, at some 375kg reduced tare, worthy contenders for fuel saving.

So let’s examine the detail, starting with the power plant. Most operators running up to 44 tonnes still select larger (typically 13 litre), lazier engines, not least because they’re proven over many years. But most tractor OEMs have at least a two-engine strategy that shouldn’t be dismissed.

As DAF Trucks marketing manager Phil Moon says: “11 litre engines may not deliver the same grunt, but there are benefits in terms of payload [180kg] and fuel efficiency [up to 3%], particularly for high-mileage operations up to 40 tonnes.” And Iveco product director Martin Flach agrees: “Modern VGTs [variable geometry turbos], etc, make smaller engines entrirely viable. We offer 9 litre engines for Stralis from 310—400bhp [1,300—1,700Nm], 11 litres from 420—480bhp [1,900—2,500Nm] and 13 litres above that.”

Which brings us on to what, for many, really matters: peak torque and hence also gearing. The vast majority of today’s truck engines deliver flatter torque curves than at Euro 5 and with more resilience at the bottom end. For operators tramping up and down the UK’s motorway network that probably makes taller, fuel-saving final drives more attractive – taking advantage of lower sweet spot cruising revs.

DAF typically suggests 2.64 rear axle ratio on modern 70 series tyres, as opposed to, say, 2.80 for Euro 5 or 2.93 on 80 series tyres. MAN talks of 2.53 for its 12.4-litre D26 in the workhorse 440—480bhp range, compared to 2.875 at Euro 5 or 2.71 on low-profile tyres. However, for hauling tipping trailers you might be better off with lower gearing: what you lose in fuel on the long haul, you’ll gain in efficiency and performance around the quarry.

Talking of tyres, Nick Handy, MAN’s sales engineering manager, makes the point that moving over from 295/80 to 315/70 not only increases axle weight capacity – meaning simpler stocking and fitting – but also futureproofs the investment. He concedes that low rolling resistance options tend to be softer (so wear faster), but adds that the fuel benefits far outweigh the costs, certainly for long haul.

“But making the right choice even among low rolling resistance tyres can yield 2—3% fuel savings, depending on the compound, tread pattern and construction,” he advises. “We fit Goodyear regionals because they’re good value, multi-purpose tyres. But for our EfficientLine2 TGX, we use Michelin X Line Energy tyres.” Other OEMs offer other preferences, but the thinking remains the same.

What about chassis and driveline? Volvo is upbeat about two introductions: a 6x4/2 double-drive lifting tag and its dual-clutch option. The former offers operators running, say, 44-tonne tipper trailers but also STGO Cat 2 heavy haulage, a very flexible choice. Yes, the tandem drive costs £3,000, but since the inter-axle lock has been replaced with a dog clutch, you get 4x2 fuel economy on part loads with the axle lifted and drive disengaged. Meanwhile, the dual clutch – available on 460, 500 and 540bhp units – is worth considering for hilly terrains. Volvo marketing manager John Comer says, with no break in torque between changes, it makes for a truck “that’s always on top of the job”. That means stress-free drivers when the going gets tough on timed deliveries.

Beyond these, two-pedal AMTs are standard list almost everywhere now, with software selections covering most operations, on- and off-road (think of DAF’s liquid transport and heavy haulage offerings). Crawler gears are also increasingly common and Volvo has just launched an ultra-low crawler too. That industry acceptance isn’t yet there for advanced engine brakes and retarders, despite their advantages not only in terms of safety but also wear, maintenance and RVs. For those who see them as not applicable, consider this: Scania’s latest delivers 4,100Nm of retardation (due to revised gearing) and, importantly, with clutched operation to eliminate drag.

Meanwhile, small midlifts are in the ascendancy and still developing. Volvo, for example, last month introduced a low-height, light-weight 6x2 pusher, with a 17.5 inch midlift taking 600kg off the ‘standard’ configuration. The small wheeled axle is plated at 4.5 tonnes (instead of 7.5), meaning a 16-tonne bogie. However, for bulk loads that’s not a problem, and Comer makes the point that it leaves space for hydraulics. The lower deck height also means flexibility for trunking curtainsiders in and out of continental Europe. Worth a thought – particularly if you know your pin load?

But tractor developments haven’t stopped at the ‘mechanical’ level. As Moon says, most OEMs introduced subtle, but important, driveline control improvements alongside Euro 6. “Acceleration limiters, predictive cruise control [automatically selecting gears, power and speed to suit terrain, mostly using GPS] and adaptive cruise control [moderating speed to match traffic] can all make a significant difference to fuel economy.”

And there’s more. MAN’s Handy points to vehicle air pressure management (based on smart compressors with clutch actuation), while Scania’s presales technical manager Phil Rootham adds Eco-roll (intelligent AMT-controlled free rolling) to the list of energy saving measures. Both are again automated, but everyone I spoke to agree that drivers need to know how to get the best out of them. Hence the importance of driver training packages on new tractors.

So, no matter how well informed you think you are, perhaps it’s time to talk to your dealerships? Best advice: start by explaining your operation and let their sales engineers help you.

Additional points

Safety kit: Consider side scan sensors, 360 degree and reversing cameras, and additional nearside door glazing (OEM and aftermarket), particularly if CLOCS matter to you.

Telematics: Whether OEM of third party, just do it. But make sure you do the analysis, engage drivers and trainers to reap the fuel, safety and insurance rewards.

Aerodynamics: Specify the kit, particularly if trunking circa 200,000km a year in top, but match it to your combinations – and review regularly. Cab gaps (siding fifth wheel adjustment) and poorly (or not) adjusted air deflector height undo all the good.

4/6x2 and tag/steer: Yes, there are applications running sub-40 tonnes where 4x2s are adequate – and there are short wheelbase manoeuvrability and cost benefits. However, the flexibility argument in favour of 6x2s is undeniable. Similarly, tags – especially rear steer – can offer off-road advantages but RV can be an issue. As for double or single steer: personal preference rules.

Chassis height and weight: It’s not just about small midlifts: with air suspension, consider omitting sliding fifth wheels and lead-up ramps.

Specification process

So how should your tractor unit specification process start? Scania presales technical manager Phil

Rootham speaks for most of the OEMs when he suggests that sales engineer be allowed to understand the application – not what you had last time. “We need to know operational aspects – journey types, speeds, terrain, etc – but also what’s being carried and what matters, including whether they’re paid by load, pallet, etc. That’s how we add value.”

Only when all relevant data has been discussed should the process move on to engines, drivelines, cab size, chassis configuration, etc. “Understanding the worst case scenario enables us to start dimensioning appropriate engine power and torque, for example. But we also need to consider commercial realities – and not only total cost of ownership and RV [residual value]. For instance, we might suggest a 400bhp unit, but if that means one less load per day, it’s probably not the most efficient solution.”

So the process throughout is one of balancing the package to best match the transport objective at lowest upfront and operational cost. “If the vehicle will be tramping down motorways, the gearbox priority is getting to cruising speed. So it’s about how we do that efficiently and then maintain low revs to minimise fuel. But if the operation is more varied, in terms of road types and speeds – or if contracts are based on timed deliveries – we need to review the engine and geartrain to optimise engine speeds and drivability, while still protecting cruising speed and fuel efficiency.”

One more thought. Rael Winetroube, head of MAN TopUsed, makes the point that fleets’ replacement policies must also be factored in. “If vehicles are kept for 24—36 months, then second life is important, so operators should consider larger cabs, higher power and top-end specifications – fridges, microwave, etc – to satisfy the retail market. If it’s five or six years then generally they’ll be sold into emerging markets, so smaller cabs and technically simple tractors make sense.”

Brian TInham

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Related Companies
DAF Trucks Ltd
Iveco Ltd
MAN Truck & Bus UK Ltd
Mercedes-Benz UK Ltd
Renault Trucks Essex
Scania (Great Britain) Ltd
Volvo Group UK Ltd

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