Ford has been using radius arms on their Superduty trucks (F250-F550) since 2005. As amazing as it sounds, they have been the exact same arm for these 17 years of production!
Though they are a great design that functions great on any stock truck. They do have a few down sides when it comes to even a slightly modified truck. Mainly that they are not adjustable in any way! Why Ford chose this we do not know. It is very strange to have a suspension component, like a radius arm that affects factors like your castor, and not make it adjustable!
The reason this is an issue is when you lift, or even level your truck, as you lift the truck the castor will change through that suspension travel. For example, a leveled truck will decrease its castor by 1 or 1.5 degrees from stock depending on the year of your truck. This change can drastically affect handling, steering wheel return and could contribute to death wobble.
The other issue comes when you install larger tires like 37s or even 35s. You can have issues with the tires rubbing the arms. Now it really has no effect on any of the components but its just annoying to have happen. You also lose a small amount of your turning radius.
You can see where the 37" tire on this truck has been rubbing pretty hard on these stock arms.
Our Radius Arms help to fix all of this! We build our arms to bolt right into the stock locations but we add the ability to adjust them to your desired castor. This can all be done without having to install ball joint shims and can be done on the ground in your driveway once installed!
We also have addressed the tire clearance issue by designing notches in the lower arms for the tire to sit. These will allow you to clear a 37" tire with stock wheel offset!
It is good to make sure you have an adjustable track bar to insure that the axle is re-centered after a lift so you do not have one side rub and one side not rub.
The arms are a fully welded unit with an internal 1/4" skeleton inside of the 3/16s outer shell and a clevis made from 1/4" plate. The arms utilize a tab and slot construction that adds significant strength to the arms.
For the pivot joint at the frame we use Ballistic Fab's 3.0 Forged Joint. This Joint is a beast! It is made to the factory width of the Ford radius arm mount and the correct 18mm bore size for the factory Ford Bolt. They are greasable and full rebuildable for many years of service! Because they use a spherical bearing captured by polyurethane, they help to isolate the truck from road vibration much like the stock bushings.
The upper arms are made with 1/4" plate for the clevis and 1.75x0.250 DOM tube with a 7/8x3/4 rod ends. This is where you get your adjustment!
You are able to use the stock bolts along with a 3/4" grade 8 bolt for the upper arms.
These arms are a great option for any Superduty with a lift or leveling kit! They provide the adjust-ability and strength that is lacking in the stock arms. Also they just look so much better than the clunky stock ones!