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Radius Arm vs. 4-Link Suspension



For this topic, we’re zeroing in on the later model (2005+) Ford Super Duty, (2014+) RAM 2500 and (2013+) RAM 3500 trucks that all come with solid axles and a coil sprung front radius arm suspension configuration. Overall this factory setup provides relative comfort and capability for everyday use. The radius arms are used to position and control the front axle movement as the suspension cycles up and down. They use a single mount on either side of the frame as well as 2 mounting points at the axle. In addition, a track bar is used to control lateral movement of the front axle and position the axle centered under the truck, coil springs to set ride height and absorb movement, shocks to control that suspension movement, in addition to components like the sway bar, steering linkage, bump stops and brakes that for the most part are compatible regardless of the suspension configuration you choose.

When it comes to lifting these Ford and RAM trucks there are a few common methods to correct the suspension geometry. The most basic option retains the OE radius arms by using a drop bracket that mounts into the frame pocket for the radius arm to lower the mounting position. BDS doesn’t offer this option as it provides no strength or performance improvements. What you will find offered from BDS are your choice of heavy duty replacement radius arms or a 4-link conversion.

Radius Arms

The BDS radius arms provide improved performance over the factory thin-wall stamped steel. They improve on the OE design constructed from 1.75” heavy wall steel tubing, gusseted for strength and formed for additional clearance of oversized tires. Mounting into the OE location these arms maximize ground clearance, these arms build in additional caster to accommodate 2-7” lifts as well as use a lower cam slot designed for easily adjusting caster to set alignment at various lift heights. They use OE style rubber bushings for quiet, maintenance free operation and better isolation of NVHs (noise, vibration, & harshness). While these radius arms are a big improvement to the factory arms, due to the single mounting point there is still caster change as the front axle cycles up and down that can lead to less-than-ideal steering feedback in rough conditions especially at higher speeds. Due to fewer mounting points the radius arm is less restricted allowing for improved articulation offroad.

Pros: improved strength over stock, caster adjustment, tire clearance, ground clearance, articulation

4-Link Conversion

Upgrading from the radius arm to a 4-link provides several improvements, both for strength and handling. A 4-link uses 2 mounting points on each side at the frame and 2 mounting at the axle. This allows the suspension to cycle up and down with relatively zero change to the caster for more predictable handling characteristics on/off-road. In addition due to additional mounting points, heavy duty (1/4” steel) 4-link brackets and high duty upper and lower control arms provide superior strength so you can use it and abuse it out on the trail. All arms use greasable bushings for easy maintenance while providing superior isolation of NVHs (noise, vibration, & harshness). This 4-link conversion is designed to correct suspension geometry for use at 4-10” of lift.The main drawback is to create optimal gemoetry and vertical separation between upper and lower arms the 4-link doesn't have as much ground clearance the OE replacement radius arm kits provide.

Pros: improved strength, better handling, caster control and adjustment, tire clearance

Which one is right for your truck? BDS offers both HD radius arm and 4-link conversions, and ultimately you can’t go wrong with either. The radius arms will be more affordable and provide more ground clearance, whereas the 4-link will offer the best on/off-road handling performance and the most strength. If you’re going with a taller kit the 4-link is preferred whereas if you are going offroad often the 4-link offers the maximum clearance and articulation. The choice is yours…

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