4x4 suspension technology

SUSPENSION TECH WITH SUPERIOR ENGINEERING

Michael Hayes reveals and explains all about 4WD suspension technology.

www.superiorengineering.com.au

Big Lifts and Caster Correction

If you own a coil-sprung 4WD, you probably under-

stand the versatility of the radius arm suspension plat-

form 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 caster.

SO WHAT IS CASTOR?

When a vehicle’s front suspension is aligned, caster is

adjusted to achieve the self-centring action of steering.

Improper caster settings will often cause vague steer-

ing response and the lack of self-centring. This, com-

bined with larger or greater offset tyres, will amplify

any slack or loose suspension or steering joint play.

POSITIVE Caster

Positive caster 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 for-

ward from the body.

NEGATIVE Caster

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.

HOW DO I FIX THE Caster?

Caster BushesCaster correction bushes replace the original front ra-

dius arm bushings and have off-centre pins that put

the caster angle back within vehicle specifications.

PROS: Cheap

CONS: Reduced bush life, reduction in suspension

travel


Caster PlatesCaster correction plates are a bolt-on adapter plate

that provides an alternate mounting hole position for

the front of the radius arm. Lower angle plates can re-

quire welding, larger plate correction angles of 6in plus

lift are generally fully bolt on.

PROS: Cheap, DIY

CONS: Added strain to the pivot pin


Drop BoxesThe ‘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, essen-

tially returning the suspension to its original geometry.

PROS: Cheap, DIY, drive-ability

CONS: Reduction in ground clearance


Dropped Radius ArmsWhen 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.

PROS: DIY, driveability, strength, clearance, articula-

tion

CONS: Cost


Hybrid Drop Box / Long ArmsThe 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.

PROS: DIY, driveability, ride, strength, clearance, artic-

ulation

CONS: Cost

CONTACT SUPERIOR ENGINEERING

Phone: (07) 5433 1411

499 Uhlmann Road

Burpengary Queensland 4505

Australia

ASK THE EXPERTS:

4X4 Suspension Tech Talk With Superior Engineering



4x4 suspension technology

Automotive