Prime Mover Buying Guide

A prime mover is the truck at the front of every semi-trailer, B-double and road train in Australia, and it is usually the single most expensive piece of equipment an operator owns. Choosing the right one starts with the trailers it will pull and the roads it will run.

Start with the combination and the weights

The key rating for a prime mover is its GCM (gross combination mass): the maximum the prime mover and its trailers may weigh together. Match it to your work, with margin:

• Single semi-trailer: general freight, often in the 40 to 50 tonne gross range.
• B-double: two trailers linked by a fifth wheel on the lead trailer, common on approved routes at higher masses.
• Road trains: double and triple road trains on approved routes in regional and remote Australia, needing a high-GCM prime mover rated for the job.
• Heavy haulage: oversize and overmass loads under permit, needing purpose-built specifications.

Access depends on the route network and the vehicle's configuration, including Performance Based Standards (PBS) approvals for some combinations. Check the National Heavy Vehicle Regulator (nhvr.gov.au) or your state road authority for the networks you need. Drivers need a heavy combination (HC) licence for a semi-trailer and a multi-combination (MC) licence for B-doubles and road trains.

Cab-over or conventional?

• Cab-over (flat-nose): shorter overall, so more trailer length within legal limits, better manoeuvrability and visibility. Common for linehaul, B-doubles and metropolitan work.
• Conventional (bonneted): easier engine access, often a smoother ride and a quieter cab, and traditionally preferred for road trains and heavy haulage in rural and remote areas.

Engine and power

Power is chosen for the weight and terrain: a prime mover on flat interstate highways at B-double weights needs less than one pulling triple road trains or heavy haulage through hills. Look at peak torque and where in the rev range it is delivered, not only horsepower. Too little power means slow climbs and driver frustration; too much means extra cost and fuel you rarely use.

Transmission and driveline

• Automated manual transmissions (AMTs) are now standard on most new prime movers, easier for drivers and often more fuel efficient.
• Manual gearboxes (such as 18-speed Roadrangers) remain popular in heavy haulage and road train work for their durability and control.
• Diff ratios should suit your weights and speeds: numerically lower ratios for highway cruising, higher for heavy loads and hills.
• Retarder or engine brake: essential for heavy loads and hilly routes, and it saves brake wear.

Sleeper cab or day cab

Linehaul and long-distance work need a sleeper, sized for how long drivers will be on the road and compliant with fatigue management rules. A day cab is lighter and cheaper, and suits local, port and metropolitan work where drivers go home each night.

Popular prime mover brands

Kenworth, Volvo, Mack, Scania, Mercedes-Benz, Western Star, Freightliner, DAF and Iveco all build prime movers sold in Australia. See our truck brands comparison for how they differ.

Buying a used prime mover

• Engine hours and kilometres, and the type of work it has done (linehaul kilometres are kinder than heavy haulage or road train work at the same reading).
• Engine, gearbox and diff rebuild history, and when the next major overhaul is due.
• Fifth wheel condition and rating, turntable wear, and chassis cracking around the fifth wheel mounts.
• Air and electrical connections for trailers, and brake condition.
• Emissions system condition on newer trucks.
• A PPSR check, current registration and inspection status.

Our guide on how to inspect a used truck covers the inspection in detail.

Ready to look? Browse prime movers for sale or search prime movers in Queensland, New South Wales, Victoria and Western Australia.