Pre-start checks, vehicle inspection and defects
Vehicle Categories, Mass and Dimension Limits
The numbers that matter
Tare mass is the empty vehicle. GVM is the manufacturer's maximum loaded mass of the vehicle itself. GCM is the maximum loaded mass of the vehicle plus any trailer it tows. Payload is simply GVM minus tare. Registration and the compliance plate restate these limits but never raise them.
Axle and axle-group limits
Under general mass limits, common maximums are: a single steer axle 6.0 tonnes; a single axle on dual tyres 9.0 tonnes; a tandem axle group 16.5 tonnes; a tri-axle group 20.0 tonnes. Tyre size and ply rating, suspension type and axle spacing all reduce these figures, so a tri-axle group on small tyres cannot legally carry 20 tonnes.
The overall mass limit is the lowest of GVM, the sum of the axle-group limits and any registered or permit limit. Concessional and higher mass limits exist but only with accreditation and, usually, road-friendly suspension.
Dimensions
Standard limits are 2.5 m wide, 4.3 m high and 12.5 m long for a rigid vehicle. Anything wider, higher or longer needs a permit or pilot and escort arrangements.
Traps
Questions love to give you a load that is under GVM but badly placed, so an axle group is overloaded. Mass must be distributed, not just totalled. Another trap is confusing GCM with GVM when a trailer is attached.
Worked example: a three-axle tipper has a GVM of 24 t and tare of 11 t, giving a payload of 13 t. You load 12 t, so you are under GVM - but if 9 t of that sits over the rear tri-axle group and the group limit is 20 t with the body's own weight included, you may still be legal here while overloading the steer axle if the load sits too far forward. Always check the distribution.
Pre-Start Checks
A legal duty, not a ritual
The pre-start check is the driver's first defence against breakdown and crash, and failing to do one can leave you exposed if a defect causes an incident. Do it the same way every time, in the same order, so nothing gets skipped when you are rushed.
The walk-around
Start at the driver's door and work around the vehicle. Check for fresh fluid leaks underneath; tyres for pressure, cuts, bulges, exposed cord, tread depth, objects wedged between dual tyres and correct dual spacing; wheel nuts and alignment indicators; lights and reflectors, ideally using a reflective surface or a second person; mirrors, glass, wipers and the horn; suspension, springs, airbags, U-bolts and shock absorbers; mudflaps, number plates and the load.
For a combination, check the coupling last but thoroughly: fifth wheel jaws closed around the kingpin, the dog clip or safety latch in place, turntable secure, air lines and electrical lead connected and not rubbing, trailer parking brake operational and the landing legs wound up.
Air brake test
With the engine running, build pressure to governor cut-out. Switch off with the service brake applied and watch the gauge over one minute - the drop must stay within the manufacturer's leak limit. Confirm the low-pressure warning operates and the park brake holds.
In the cabin
Seat and belt adjusted, all warning lights extinguish after start-up, gauges reading normally, fire extinguisher, warning triangles and first aid kit present, and mirrors set for the load you are carrying.
Rule of thumb: if you would not be confident signing your name to it, do not drive it. A defect found in the yard costs minutes; one found at highway speed costs lives.