Understanding Truck Drive Axles: A Comprehensive Guide

What is a Drive Axle?

The drive axle provides motive power by transmitting the engine’s power to the road via the tyres. It connects to the engine through the gearbox, driveshaft, and axle, allowing the truck to move forward or backwards. Trucks can have multiple drive axles depending on their intended use and requirements.

Truck Types and Their Axle Configurations

Rigid Trucks

• Typically feature one or two steering axles at the front
• Have one or two drive axles at the rear
• May include a tag or lift axle (non-driving)

Combination Trucks

• Consist of a tractor unit or rigid truck pulling a trailer
• Can pull either a semitrailer or full trailer
• In New Zealand, tractor units usually have:
  • One or two steering axles
  • One or two drive axles

Understanding Axle Configuration Notation

Axle configurations are expressed in the format: axle ends × driven axle ends. Each axle has two ends where the wheels are located. For example:

• In a 4×2 configuration:
• 4 represents total axle ends (2 axles)
• 2 represents driven axle ends (1 drive axle)

Common Axle Configurations

Light to Medium Duty

• 4×2
  • Two axles total
  • One drive axle
  • Common for light freight
  • Typical configuration for small box trucks
  • Light-duty tractor units (e.g. pulling empty containers on skeletal trailers)
• 4×4
  • Two axles total
  • Both axles driven
  • Used for power line service trucks
  • Suitable for light off-road work

You’ll see some off-road vehicles, like Land Rovers, called 4x4s, and this is for the same reason.

Medium to Heavy Duty

• 6×2
  • Three axles total
  • One drive axle
  • Popular for medium road freight in tractor unit form, or popular for larger rigid metro trucks and curtainsiders
• 6×4
  • Three axles total
  • Two drive axles
  • Standard for heavy road freight in tractor unit form and many tipper trucks in rigid truck form
• 6×6
  • Three axles total
  • All axles driven
  • Specialised use: military, fire trucks, off-road

Heavy Duty and Specialised

• 8×2
  • Four axles total
  • One drive axle
  • May include lift axles (8×2-6 variant)
• 8×4
  • Four axles total
  • Two drive axles
  • Common for heavy road freight and logging in tractor unit format
  • Popular for tipper trucks in rigid format
• 8×6
  • Four axles total
  • Three drive axles
  • Used for road trains and heavy haulage overseas when in tractor unit form
  • Specialist tow trucks
  • Better traction in challenging conditions

Specialised and Heavy Equipment

• 8×8
  • Four axles total
  • All axles driven
  • Military and specialised applications
• 10×4
  • Five axles total
  • Two drive axles
  • Used for truck-mounted cranes, mobile cranes and specialised flatbed applications
• 10×6
  • Five axles total
  • Three drive axles
  • Mining, mobile crane and off-road applications

Choosing the Right Configuration

The selection of drive axles depends on:

1. Operating environment (urban vs. off-road)
2. Load requirements (overall weight and weight distribution)
3. Surface conditions
4. Type of freight.

General Guidelines:

• Single drive axles: Suitable for urban and highway operations
• Multiple drive axles: Better for:
  • Soft surfaces
  • Forestry work
  • Mining operations
  • Heavy-duty hauling
  • Oversized loads

Note: It’s not always possible to visually determine the number of drive axles on a truck without knowing its specifications or configuration code. A good way to check is by looking for axles and differentials (but this is difficult to see on 8×4 tractor units).

In general, the fewer axles you have and the fewer driven axles, the cheaper the truck will be to run. However, you must be sure not to overload the truck or its axles.

To calculate what you can carry with your axle configuration, this axle weights course shows you everything you need to know.