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Heavy haulage has seen a gradual shift from 6x4 double-drive tractors to 8x4s. Geoff Ashcroft
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learns what's on offer and what operators think.
With the possibility that reduced axle loadings may be thrust upon the heavy haulage industry, there is a growing trend for 8x4 tractors as operators look for ways of spreading fifth-wheel loads over more axles. First, let's see what the major manufacturers are producing...
Volvo
Aware of the move towards 8x4s -it now sells as many 8x4 tractors to the heavy haulage fraternity as it does 6x4s -Volvo's on the ball.
"An 8x4 avoids the need for a costly load spreader dolly, which makes a combination much more difficult to manoeuvre than an outfit using just one fifth wheel," says Volvo Truck heavy haulage specialist Chris Dove.
The firm's factory-built 8x4 starts life essentially as a 4,300mm rigid tipper truck chassis but ends up fully type-approved as a tractor. complete with tapered rear frame rails and fixed or sliding fifth-wheel coupling.
Typically,an 800-litre fuel tank and toolboxes are installed on the platform behind the cab.The Dl 6 engine is available with outputs of 540,580 or 660hp; the first two can be equipped with manual transmissions, but the 660 is offered only with a 12-speed 1-Shift box.
"Despite T-Shift's sophistication for driveline management and the ability to handle massive torque loadings, it lacks a crawler gear." says Dove. "In some applications, this could mean that first gear -or even reverse -is too high. If so, operators would need to specify the 580hp version of the D16 coupled to our V02814 manual gearbox."
Volvo's T-Ride, double-drive bogie is fitted at the rear, along with heavy-duty hubreduction axles and additional leaf springs to cope with increased loads.This system offers a 36-tonne design weight for the bogie-three tonnes more than the current legal maximum soil operates well below its 100% load rating.
"Heavy hauliers prefer steel springs, although greater ride comfort and operational sophistication are possible with an airsuspension system," says Dove. "But with 26 tonnes as the design limit for an air-ride bogie, the only way we can make that system available to heavy haulage is with lower maximum permitted axle loadings," Dove adds.
"The integration of ride height sensors on an air suspension system allows the use of different gearchange strategies with I-Shift, so the transmission can vary its shift points according to load," he says.
Potential drawbacks of the 8x4 tractor include reduced manoeuvrability (anyone who has ever driven an eight-wheel tipper will know about the space that needs, let alone with a multi-axle trailer behind), and the inability to lift an axle for increased weight transfer and additional traction.
"Then you need to look at a 3,900mm 6x4 and get a fourth-axle conversion from someone like Dutch firm Estepe." Dove explains."Estepe relocates the air and fuel tanks and installs a power-steered. airsuspended lift axle in their place, between the steering and first drive axles. This results in a more manoeuvrable tractor, with the ability to dump air from that extra axle and gain a massive amount of extra traction — useful in an off-road environment."
Operator reports
Tim Martin of Be I ast-based MarTrain Haulage runs three Volvo 8x4s.13,vo are F'H12s, while the flagship is a 610hp FH16.
"The 8x4s enable us to handle the high imposed loads with much greater simplicity than a 6x4 with dollies," he explains,"We do run dollies, but there's less complexity in the system if we can run with just a tractor and trailer."
He believes manoeuvrability isn't an issue, given the loads he frequently carries throughout the UK and the rest of Europe.
"These trucks are quite controllable with a manual gearbox," he adds. "They're less complex than some on the market, and can be relatively easily serviced and repaired."
"Our local dealer's understanding of the trucks is second to none,he continues, "which has played a big part in us running a predominantly Volvo fleet."The 16-strong fleet also includes a couple of Mercedes.
"We looked at the Mere Titan.but preferred the simplicity of the Volvo," Martin says."We've never struggled with offloading a used FH — they always have a decent residual value."
While fuel economy is secondary to getting the job done, Martin watches the figures.As the numbers drop sharply when the combined weight goes over the 100-tonne mark (the FF116 and trailer tips the scales at 53 tonnes unladen), there are times, he says, when many operators would simply choose to turn away. But he says he "just likes to know".
"I'm happy with 4mpg at 100 tonnes, but we've seen fuel economy dip to 1.2mpg when the FH16 works hard at its 180-tonne rated maximum.' he reveals.
Receiving particular praise, however, is Volvo's integral engine brake, or VEB.
"The retardation we get is fantastic— but then again, so is the performance with 610 horses up front," Marlin tells us. "Why anybody would want such power at regular weights is just beyond me.
"Our FH16 is more than comfortable with any amount of weight we put behind it. which can be up to 180 tonnes with 13 axles following."
Meanwhile, another company, Carter Haulage and Storage of Kings Lynn. Norfolk. has responded to the increasing weight of customers' construction plant by adding a 125-tonne GCW,Euro-4-compliant Volvo FT-116-660 to its 14-strong mixed fleet, Shaun Carter says that with plant becoming heavier, the firm has had to increase its carrying capacity, along with the amount of muscle it has up front.
The 6x4 double-drive F1116-660 tractor is not shy on specification: the equipment list ranges from an I-Shift automated gearbox to full rear air suspension. •