9.4 Vehicle Weight, Payload & Axle Loading

9.4 Vehicle Weight, Payload and Axle Loading

Driver CPC objective 1.6 for category D drivers requires the ability to load the vehicle with due regard for safety rules and proper vehicle use, covering forces affecting vehicles in motion, gearbox ratios according to load and road profile, automatic transmission systems, calculation of payload, load distribution, the consequences of overloading an axle, and vehicle stability and centre of gravity. Drivers often assume this objective belongs to lorry drivers. It does not. A coach on a continental tour with 49 passengers, 49 suitcases, skis, and a full fuel tank is a loading problem, and overloaded coaches are a recurring cause of DVSA prohibitions.

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The Plate: Where Your Legal Limits Come From

Every PCV carries a manufacturer's plate (and, for most vehicles, a Ministry or DVSA plate) that states the legal maxima. These numbers, not the driver's judgement, define overloading.

You can be legal on GVW and still be illegally overloaded on an axle. This is the single most important loading fact for a coach driver, because passengers and luggage are rarely distributed evenly.

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Calculating Available Payload

Payload is what is left once the vehicle itself is accounted for:

  PLATED GROSS VEHICLE WEIGHT
     minus  Unladen (kerb) weight of the vehicle
     minus  Fuel, AdBlue, water and driver
   ========================================
     =      AVAILABLE PAYLOAD for passengers, crew and luggage

A Worked Coach Example

A 53-seat touring coach has a plated GVW of 19,500 kg and a kerb weight (including a full fuel tank and the driver) of 14,200 kg.

• Available payload = 19,500 - 14,200 = 5,300 kg
• Using the conventional allowance of 68 kg per passenger used for PSV capacity purposes, 49 booked passengers weigh 49 x 68 = 3,332 kg
• Remaining allowance for luggage = 5,300 - 3,332 = 1,968 kg
• Divided across 49 passengers that is just over 40 kg each — before any tour courier, ski bags, or bulk equipment.

The exam point is the one the arithmetic makes for you: a full coach with heavy luggage can be close to its plated limit, and a driver who accepts "just a few more bags" at the last pickup may push it over. If in doubt, a weighbridge check is the only defensible way to prove compliance.

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Load Distribution and Axle Overloading

Luggage lockers run the length of a coach, so where bags are stowed changes the axle loads even when the total weight is unchanged.

Consequences of Overloading an Axle

• Braking: brakes are designed around the plated axle weight. An overloaded axle takes longer to stop and generates more heat, which brings on fade sooner on a descent.
• Tyres: each tyre carries a load index. Exceeding it causes heat build-up, carcass failure, and a blowout that, on a coach front axle, is very frequently catastrophic.
• Steering and suspension: an overloaded front axle makes steering heavy and wears king pins and bearings; an unloaded front axle makes it vague and reduces steering grip.
• Enforcement: DVSA operates weighbridges and portable axle weighers at check sites. An overloaded PCV attracts a prohibition, a fixed penalty or prosecution, and a report to the Traffic Commissioner against the operator's licence.

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Gear Selection According to Load and Road Profile

The syllabus links loading directly back to transmission use, and the reason is physical. A vehicle at plated weight needs:

• a lower ratio for the same gradient than the same vehicle running empty;
• an earlier downshift before a climb, because momentum is lost faster once the engine falls below the torque band;
• more descent planning, because the same brakes must now absorb far more kinetic energy — kinetic energy rises in direct proportion to mass, so a coach at 19.5 tonnes carries roughly 37 per cent more energy at the same speed than the same coach at 14.2 tonnes.

A driver who drives a full coach exactly as they drive it empty will arrive at the bottom of a long descent with hot brakes.

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The Driver's Practical Loading Duties

1. Know the plated weights of the vehicle you are driving today, not the one you drove last week.
2. Supervise stowage rather than leaving it entirely to passengers or a courier: distribute heavy items across lockers and keep them low.
3. Refuse what you cannot carry legally. A polite refusal at the kerb is infinitely better than a prohibition at a check site with 49 passengers watching.
4. Secure the load so nothing moves under braking, and warn anyone opening a locker that contents may have shifted.
5. Reconcile luggage to passengers at every stop. This is a loading duty and a security duty at the same time (see section 12.2).
6. Re-check after a mid-route pickup, which is when an already full coach is most likely to tip over its limit.