4WD Suspension Technology

If you own a coil-sprung 4WD, you probably understand the versatility of the radius arm suspension platform and just how well they can handle most off-road conditions. When you lift a radius arm vehicle, the arms are fixed to the diff and the rear pivots around the chassis bushes. This added lift causes the diff to rotate and effectively reduces the castor.

So what is castor? When a vehicle's front suspension is aligned, castor is adjusted to achieve the self-centring action of steering. Improper castor settings will often cause vague steering response and the lack of self-centring. This, combined with larger or greater offset tyres, will amplify any slack or loose suspension or steering joint play.

Positive castor is when the steering knuckle pivot points of the diff are angled such that a line drawn through them intersects the surface slightly ahead of the contact patch of the tyre. This makes is easier to drive and improves directional stability. An example of positive caster is the front forks on a bike that tilt forward from the body.

A 4WD with negative caster will tend to be easier to steer but will lack directional stability and handling, like a wheel on a shopping trolley. The vehicle will also be easily affected by any track surface variation such as small irregularities or bumps.

CASTOR BUSHES

Caster offset bushes for radius arms are a practical and cost-effective solution to correct wheel alignment after fitting a suspension lift to your 4WD. Offset bushes are pressed into the radius arms to adjust the angle back towards factory settings, restoring stability and steering feel.

PRO: They can be a cheaper alternative.
CON: They can lead to reduced bush life, and reduced suspension travel

CASTOR PLATES

Caster correction plates are a simple yet highly effective upgrade for lifted 4WDs, restoring proper wheel alignment after a suspension lift. When a vehicle’s suspension is raised, the caster angle often moves out of factory specification, leading to vague steering, poor tracking, and increased tyre wear. Caster plates are designed to correct this angle, bringing back stability and control both on-road and off-road. They’re an affordable alternative to full replacement Radius arms, making them a popular choice among 4WD enthusiasts who want sharper steering response and improved handling without compromising suspension performance.

PRO: They are affordable and DIY.
CON: They add strain to the pivot pin.

DROP BOXES

The 'Drop Box' is a fabricated alternate rear mount for the radius arm. This mount lowers the rear mount of the arms to counteract the same amount of lift, essentially returning the suspension to its original geometry.

PRO: They are affordable, DIY, and improve drive-ability.
CON: They can reduce overall ground clearance.

Radius Arms

When performance matters most, dropped radius arms accurately correct caster and also address the pin or bush mounting geometry to allow for maximum wheel travel and greater handling. As well as correcting caster, added design features such as Superior Engineering's Superflex mounting technology can also be incorporated to dramatically increase wheel travel in radius arm type vehicles.

PRO: They are DIY, strong, improve drive-ability, and maximise articulation.
CON: They can be a more costly option.

Hybrid Radius Arms

Superior Engineering has developed a combination Hybrid Long-arm Drop box style radius arms. The extended arc of the longer flatter arm allows the suspension to properly soak up the bumps, and the new drop box that changes the mount orientation to a radial rear bush. Combine this with Superflex mounting and wheel travel is massive while still retaining excellent manners.

PRO: They are DIY, strong, improve drive-ability, and maximise articulation.
CON: They can be a more costly option.