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Radius Arm Types and Benefits

by Superior Engineering

Michael Hayes brings us up to speed with the latest and greatest in radius arm technology from Superior Engineering!

If you own a coil sprung Patrol or LandCruiser, you probably understand the versatility of the radius arm suspension platform and just how well they can handle most off-road conditions making them one of the most popular OE link suspension systems used in large solid axle 4WDs.

This suspension uses two lower arms that attach from the frame down to the axle. At the axle, these arms attach both above and below the axle's centre line or in the case of a Patrol/Cruiser in front and back. These attachment points keep the axle from twisting under the vehicle. Wheel articulation is often limited due to link or bush binding, an inherent problem with this system. When articulating, one wheel pushes up and the other drops, which cause the links to twist the housing along its axis, much like a torsion bar. In addition to these two links a panhard rod is also used to keep the axle centred under the vehicle from lateral forces.

OE or factory radius arms are most commonly made from cast steel in the form of an 'I' section, fabricated or pressed sections have also been tried over the years. Although the weight of the arm is important, the strength and sectional modulas (area/size) are crucial design elements to ensure vehicle safety in emergency situations or when pushing the limits off-road. Thin plate arms or those made from tube do look cool but are marginal in terms of strength when you need it most. This is usually the case when your 3t+ loaded up family tourer drops a wheel down off a rock and all the weight is absorbed by the arm.

The types of radius arms and their configurations are generally based upon how they are mounted at both the chassis and diff ends. Chassis mounting styles include transverse bush (ie. Toyota 80 series) or longitudinal pin/top hat bush (ie. Patrol/LandRover). Diff mounting styles such as the twin transverse bush is the most common and is used in Toyota, Nissan, LandRover and Suzuki, other styles such as C-bushes (Ford) are also used.

Now days we are spoilt for choice when we need alternative radius arms for our solid axle 4WDs, with new designs not only correcting the castor issues associated with adding a higher lift, but adding other significant benefits to the vehicles overall performance both on and off-road. In the never ending search for added flex, the majority of available radius arms offer only very minimal benefits due to retaining OE mounting points and bush configurations, however there are some alternatives that definitely fit outside the box! When it comes to improving off-road ability there are a few key design objectives; Firstly, driveability (handling/comfort & control) followed by stability, ground pressure and power transfer.

The revolutionary Superior Engineering SuperFlex arms are a blend of two different styles of arm, each complimenting the angles of deflection required for controlled flex. The key is to change the planes of deflection to allow full movement and resist the terrible binding and tearing of bushes that occurs. Another feature is the transmission of complimentary torque back into the chassis to reduce the sway that link (3, 4 or 5) or pivoting/ wristed radius arm setups produce. The ability to maintain excellent driveability is the key to success in the SuperFlex radius arm system. The changes in bush type designation and orientation on the SuperFlex arm allows dramatically increased controlled deformation. The adapter plate allows a change in bush position which provides a larger range of allowable flex before binding, whilst still providing adequate 'feel' back into the chassis. Typically, as radius arms flex they subject the bushes to a converging load which tends to tear the bonding and cause premature failure, with the SuperFlex arm, the bushes are mounted in a different plane (vertical) which has a much greater range of motion and therefore allows the suspension bushes to pivot with reduced restriction and less side loading, increasing component life. The arms themselves are also designed with accurate caster correction built into the design, alleviating any loads on the bushes, further increasing suspension life and aiding in correct steering geometry.

Another breakthrough in design is the Superior Engineering Hybrid radius arms which are designed to combine the benefits of the SuperFlex arm technology and the improved high-speed handling of a drop box style mounting. This allows the arms, the ability to soak up the bumps and keep the wheels planted without sacrificing the maximum articulation that the SuperFlex arms can provide. With a keen eye on performance, Superior Engineering has developed a drop box mounting for GU and GQ Patrols that is nearly 20% lower profile than any other on the market. This specially designed mount allows the radius arms (standard or SuperFlex) to be substantially longer than a factory arm which further aids articulation and handling. The rear arm bushing has also been upgraded to a radial type bush rather than the failure prone pin type mount.

As with any suspension modification, contact your local suspension professional for help and ideas on what best suits your needs.

Toyota Landcruiser Standard Radius Arms made by Superior Engineering
Toyota Landcruiser Standard Radius Arms made by Superior Engineering
Nissan Patrol Superflex Radius Arms made by Superior Engineering
Nissan Patrol Superflex Radius Arms made by Superior Engineering
Nissan Patrol Hybrid Superflex Radius Arms with Drop Boxes made by Superior Engineering
Nissan Patrol Hybrid Superflex Radius Arms with Drop Boxes made by Superior Engineering
Toyota Landcruiser Superflex Radius Arms made by Superior Engineering
Toyota Landcruiser Superflex Radius Arms made by Superior Engineering

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Phone: (07) 5433 1411
1/116 Lipscombe Road
Deception Bay Queensland 4508
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© Copyright Superior Engineering

Date Published: 2015-11-06

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