The eight wheeler has always had a limited niche in the truck market, but Scania is trying to change all of that with a specification to compete in the 6×4 rigid market. Diesel News took the new 8×2 rigid out for a spin.
Regulations about axle weight limits and concerns over manoeuvrability have often hampered the eight wheeler truck in the Australian market. The regulations have a three axle rigid running at 22.5 tonnes on general access, but the four axle rigid only gets 26.5 tonnes GVM on the same roads. The higher tare weight, of four axles, reduces any payload advantage.
It is also safe to say the steering geometry of twin steer trucks in the past has left a lot to be desired. Not only were they limited in steering cut, making manoeuvrability an issue, but the imprecise geometry also made extra tyre wear an issue.
In the last fifteen years or so, the technical improvements in twin steers have come on in leaps and bounds, but the internal prejudices within the Australian truck market had already moved away from the eight legger. The die had been cast.
This year, Scania are making a point of talking to operators about bringing back the twin steer. The truck in question is the P 310 8×2 with a lifting tag axle. The specification has been honed down to make this truck a viable option to the buyer of the typical 6×4 or 6×2 distribution truck.
Using just a single drive axle reduces the overall tare of the truck, maximising its GVM advantage over the 6×4. The single drive should also reduce fuel consumption to a figure highly comparable to the 6×4, if not the 6×2. Fitting a lifting axle should alleviate any traction concerns when a tag axle is fitted.
Finally, having a twin steer configuration helps to avoid the issue which dogs many distribution fleets. As a load diminishes during the day and the goods are unloaded via the back door, the load over the front axle gets higher and higher. It’s not hard to push well past the 6.5 tonnes mass limit once some of the rear pallets have been removed.
As a result of this issue, the load may have to be loaded more carefully and the driver may have to move pallets back and forth during the day to ensure legal axle masses. Adding in the fourth axle means the chances of accidentally unloading the truck to the point where there is more than 11 tonnes over the front end, is virtually impossible.
Diesel took an 8×2 tautliner out for a test drive around the Brisbane area to get an idea of how well this configuration can fit into the niche, currently owned by the six leggers. With highway driving to the top of Cunningham’s Gap near Warwick, plus some urban driving in the city of Brisbane, the route was designed to show us just what this set-up can do.
Speccing the Truck
The truck tested is the one which was on the Scania stand at the Brisbane Truck Show earlier this year. Since then it has been doing the rounds of a number of fleets, allowing them to assess the feasibility of such a configuration.
This is an 8×2 rigid fitted with a 14 pallet 9.1 metre curtainsider body giving the truck an overall length at 11730mm. The body comes as part of the Scania ready built range, which sees the Swedish truck maker offering ready-to-go packages, something more commonly seen in the lighter end of the market with Isuzu, Hino and Fuso offering off the shelf light duty tippers etc.
Power comes from the Scania nine litre engine rated at 310 hp (228 kW) with maximum power coming at 1900 rpm. Torque is available at 1550Nm (1143 ft lb) between 1100 and 1350rpm. This five cylinder engine can be specified from 250hp to 360hp. Those looking for more power can go to the 13 litre engine and on up to a maximum of 450hp. The engine uses a single stage turbo, an SCR unit cleans up the exhaust gases and the engine is coupled to the Opticruise 12 speed AMT with a direct drive top gear.
A front end like this is unusual to see in the Australian market, but quite common around the world. It uses Scania’s four bag air suspension, rated at 14.2 tonnes. Rear suspension is also a four bag, but this one is rate at 19 tonnes. The Scania system enables a axle mass read-out at all times on the dashboard.
The lifting tag axle will automatically raise when the air system senses the axle weight on the rear is low enough for it to be raised legally. In an awkward situation where a driver feels the traction may be compromised with the axle in the down position, a button allows the driver to dump 30 per cent of the air in the system, for a limited number of seconds, to throw mass onto the drive axle, where the traction is needed.
Testing the system when parked up and watching the weight transfer from beside the truck, it is possible to see the effect clearly. When the weight goes off the lazy axle, its tyres can be see to return to a perfectly round shape, while the drive axle tyres’ deflection increases as the mass is loaded onto it.
Actually out on the test route it was possible to test out this system in a number of situations. One useful option is to press the button to take the weight off the tag axle when involved in tight manoeuvring. With the traction decreased on the rear axle, the steering does not have to work against any rear axle tyre scrub and the responsiveness to steering inputs is improved. It turns more like a 4×2 than an 8×2.
The button controlling this system is actually positioned down low, near the driver’s left knee. In fact, it would be more useful placed in a more ergonomically efficient position, making it easier to activate the system while driving without the driver having to take their eyes off the road.