Conventional Contenders

conventional contenders

The short BBC conventional B-double prime mover market is dominated by Kenworth, especially with the T610 arriving, but there are other conventional contenders in this segment. Diesel looks at two of these, the International ProStar and the Western Star 5800FE, to see what they have to offer.

There is little doubt the B-double prime mover is a dominant part of the Australian truck buying scene. The strict constraints of the dimensions on a B-double, both the overall length and the  kingpin to rear of trailer dimension force compromise on truck designers. 

The B-double is normally expected to run high kilometres, so needs plenty of fuel capacity. This puts pressure on getting the front axle mass just right. On a conventional, a set forward axle can often struggle to end up getting to the 6.5 tonne limit, whereas the set back one can get there with if the fuel tanks are placed carefully. At the same time cabover prime movers often struggle to get under 6.5 tonnes, with all of the equipment placed over the front axle.


conventional contenders


Operators are always looking to maximise productivity, so a 34 pallet B-double is the minimum requirement and a 36 pallet set-up desirable, if often almost impossible to achieve satisfactorily. The space between the front of the trailer and the rear of the cabin can often get pretty short. This is good for fuel economy but problematic for air lines and cables on an articulated vehicle.

Next, there’s the big engine. Australian truckies reckon they need a 15 litre engine at least to pull up to 68 tonnes in a B-double. The common belief is the power must be up into the mid 500s and up past 600 hp to get the job done. 1850 ft lb, thats over 2500 Nm, of torque are also minimums in many people’s minds.

The fact is, many B-double run with prime movers below these ideal levels, but there is a clear perception durability is compromised if the power is below the magic 550 mark. Well performing trucks with horsepower in the 400s, in the past, managed B-doubles over hundreds of thousands of kilometres, but are now considered a liability as trends have changed.

These very specific rules a B-double prime mover must meet also affect the buying decisions for other prime movers. An important part of those buying decisions are about improving utilisation. Therefore, if an operation is looking at a prime mover to pull a single trailer, or even an A-double it also wants the truck to be capable of handling B-double work, if needed.


conventional contenders


Going Conventional

When the B-double first appeared the cabover was considered the only way to go and, in fact, the 25 metre overall length limit meant the choice was between a cabover or a short bonneted day-cab conventional. Going to 26 metres in length back in the early noughties meant the opportunity to have a conventional with a small sleeper pulling a B-double set.

Those early conventionals were designed by squeezing down existing designs to get the BBC dimension down low enough to get the truck over the line. The following 15 or so years have seen B-double requirements being built into the design of conventionals for the Australian market.

The most obvious example of this is the Kenworth T610, but there is also the Freightliner Coronado 114. These designs moved the cabin forward over the engine compartment to make enough room to build a useable sleeper in the remaining real estate left with the BBC constraints. Judging by the number of T610s this driver saw on the highway while testing the ProStar and 5800, the reconfiguration is paying dividends.

The factors which have led to the International and Western Star offering in the conventional B-double prime mover are not all about the B-double constraints. In fact, it is more about the obsession of US truck operators with fuel economy. They will good money to shave a couple of cents off their cents/kilometre. 


conventional contenders


This led to clean aerodynamic lines and shortening the bonnet actually helps in this regard. The standard semi prime mover in big fleets in the US has a shorter bonnet and a much more slippery overall look. This became evident in the ProStar when it came out in the US and has carried over into the LT Series which has superseded it. The 4800 in the US also developed cleaner lines, going to internally mounted air cleaner and a downwards exhaust.

From these base models developed for North America it was a relatively short step to a specification which meets B-double needs. All of the basic requirements were available, they just needed to be put together in a different order.

The result is two recent models which are claiming to be contenders in a crowded market place, the B-double prime mover. One comes from a brand which has only recently relaunched in the Australian market, but has a long history in Aussie trucking, the other comes from a brand which made massive gains in market share at the beginning of the century, but which has seen that slip as truck buying trends have moved on. The Western Star 5800FE marks a departure for the brand with little bling and hidden air cleaners. 

Do these trucks have what it takes to be real contenders? Is the competition too fierce from the major players to allow a new brand in? These two models do not have pretensions to be anything other than good solid performers, which can work on Australian roads.


conventional contenders


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