Right Driver

What’s a self-steer steering axle?

A self-steer or rear-steer axle is an axle which passively steers in response to the direction of the vehicle to assist with cornering. This has the advantage of:

  1. Reducing the cornering radius
  2. Improving fuel economy through less drag by up to 1%
  3. Reducing tyre wear by up to 1 tyre per 25,000km.

The wheel can be set with maximum angles approaching 30 degrees.

Self-steer axles are especially useful on long semitrailer where they can be found in tri- and quad-axle configurations.

The axle can be locked in the forward position by the driver switching the lock switch on the side of the vehicle.

Steering axle is locked

What vehicles use self-steer axles?

The types of vehicles that benefit are:

  • Longer vehicles that need to be more manoeuvrable
  • Vehicles with many axles where tyre wear becomes a problem
This tautliner is turning and you can see the rear steer axle facing more this way to help the trailer turn around. The front wheel in the quad set still scrubs significantly

The types of vehicles that over (or always) have self-steer axles are:

  • Semitrailers (tri- and quad-axle)
  • Buses and coaches with three axles
  • Rigid trucks with two or three rear axles, e.g. 6×2, 8×4, 10×4

Large mobile cranes (up to 9 axles) often have steering on all or most axles, but they are not self-steer, it is active, speed-dependent steering that can either tighten the turning circle, reduce rear swing, or crab sideways.

Hydraulic module trailers, which are used to transport very heavy and/or very large loads, have independent steering on each axle.

Some cars in the ’80s by Mazda and Honda had four-wheel steer (e.g. Prelude), but this was abandoned due to it being expensive and overly complex in relation to the results it delivered.

Darren has owned several companies in the automotive, advertising and education industries. He has run driving theory educational websites since 2010.

Posted in Advice