TECHNICAL TOPIC: CARLI SUSPENSION 6" RADIUS ARM EXPLAINED

DATE WRITTEN: OCTOBER 10, 2012

Carli Suspension is a company that has made a house-hold name for itself in the off-road world, bringing to market some of the most advanced, best performing suspension systems for Dodge Ram HD’s and Ford SuperDuty’s.Even with the tremendous growth of the company over the last few years, their philosophy hasn’t changed:build suspension systems that provide superb on and off-road performance, in various formats to suit nearly any driver.What really separates Carli from other suspension companies is that they refuse to sacrifice ride quality when lifting a truck.With a Carli kit, you can be assured that the truck will ride BETTER than factory, compared to most other companies that are merely concerned with getting the truck in the air to allow fitment of larger tires.

Recently, Carli suspension released a kit that has made some serious waves in the off-road industry, the 6” radius arm system for 2003 through current Dodge Ram 2500 and 3500’s.This was Carli’s first endeavor into a system that provides more than 3” of lift for Dodge Rams, and they needed to ensure that it would live up to the Carli name.After tireless efforts and countless models on how to build such a system, a decision was made, and success occurred on the shop floor of Carli Suspension in Orange, California. This decision was that, in order to hold true to the Carli name, this system would feature a long travel, radius arm design, and history was made.

Fortunately, we at Diesel Power Products, had the opportunity to get one of the FIRST production kits to leave Carli Suspension.And to say the least, this kit performs like none other.All of us here have owned various lifted trucks over the years, and all had the same woes of owning these trucks, they ride like a chuck wagon.This has been one of the great things about being a Carli dealer, is that we were finally running suspension worthy of calling it suspension, but we still missed the lift height of some of the “other” kits.So, to say we were anticipating the release of the 6” radius arm system would be an understatement. And when the kit finally arrived to our shop for us to pick over, every single kit component was a work of art.The installation was smooth and the end result is nothing short of perfection.It’s got gobs of clearance (we’re running 42’s with the help of fiberglass fenders) and it rides like a Cadillac…..LITERALLY!No more would we have to compromise ride for lift, we could now have the best of both worlds thanks to the gang at Carli Suspension.

We recently had the opportunity to sit down with Shaun Quisenberry, the Operations Manager of Carli Suspension, in order to ask some particular questions in regards to this kit, and he came back with some very insightful information.Here’s what he had to say:

1.)Why is a long arm style kit necessary at 6″ of lift?What separates a 6″ needing long arms, versus 3″?

Long arms and radius arm systems are necessary to overcome the drawbacks of a short arm system. Because the long arm/radius arms are flat in relation to the ground they will not push the axle forward “into” a bump as the axle compresses upward, instead they will move up and down in more of a linear fashion. The long length makes the axle swing in less severe arc when compared to the short arms, which also improves ride quality significantly. 3″ Kits have less of an angle on the control arms, which means you can get away with using short style arms. However, even a radius arm setup would be advantageous here as well for the same reasons.

2.)Why do so many “other” manufacturers offer a 6″ with short arm?Is it merely a cost, and what are they sacrificing by sticking with short arms at 6″ of lift?

Any 6″ system will require something to be done for the factory control arms in order to maintain proper axle centering in the wheel well. To keep it simple, some manufacturers will sell longer versions (still considered “short arms”)of the factory style control arms. This addresses the problem of axle centering front-to-rear in the wheel well, but the solution brings along inherent problems in ride quality. The short arms on a 6″ lift will be angled downward at ride height to begin with, and when paired up with the severe short arc that the arms will swing, the axle will get pushed into an obstacle which will create a harshness and bounce that is impossible to overcome or mitigate. It is similiar to why Jeep guys will “flip” their shackles to the rear of the front leaf springs.It will allow the axle to swing away from the bump, not directly into it.

3.)Why did you choose to opt for the radius arm setup, versus a traditional upper and lower control arm?

When we came down to determining which style of arms to use with our 6″ Systems, we had two main concerns:First is that we need the ability for the truck to be returned back to stock. The second is that we had to account for the natural bind that happens on all coil-sprung solid axle vehicles as they articulate. As we looked into our options, we came to the realization that the Radius Arm design will address all of our needs. The Radius Arm allows us to run low profile arms that can tuck up underneath the frame and will NOT make contact with the factorylower control arm mount while the axle is fully compressed. No other long arm or radius arm on the market can do this, they all require the cutting and removal of the factory control arm mount from the frame. The Long Arm setups also require clearance of the upper control arm at the body mount.The only way to get enough clearance between the body mount and the Long Arm is to employ drastic and strength-reducing bends into the upper arm, cut and trim the body mount, and put very large bump stop drops in the front to physically limit the amount of up-travel the axle can see. None of those scenarios were acceptable to Carli’s engineering department. During the design process, we incorporated as much internal bracing and reinforcing we could fit; the end result is a radius arm design that will outlast the truck.For unsurpassed strength, we incorporate a custom crossmember(s) that ties both the radius arm drops together to the factory crossmember. With the precise fitment of the radius arms nailed down, we turned to the issue of the bind.All Long Arm and Radius Arm setups will display some sort of axle bind as one side of the axle goes up and the other goes down:one side will push forward as it goes up, and the other will pull rearward as it droops down.This movement must be accounted for in some way; failure to do so will result in catastrophic destruction of the arms. Running simulations gave us an exact measurement of how much “deflection” we needed to allow forand immediately realized that a bushing would not only get destroyed quickly, but would still only allow a “small” amount of deflection. Our solution was to turn the radius arm into a “3-link setup”, where one arm holds both the upper and lower mounts of the axle to prevent rotation, while the other arm holds only the bottom of the axle to locate it.This design allows the axle to move unhindered with zero bind. We found out quickly why Dodge never intended to run these heavy trucks as a 3-Link; they exhibit a biased dive. Our solution became the “Baby Bilstein”, or Axle Control Shock.

4.)What’s up with that so-called “baby Bilstein”?

The Axle Control Shock is a special shock designed and tuned by Carli Suspension to fit in the radius arm, connecting to the axle in what would be the 4th Link position. This very special shock resists the momentary forces of the body diving, but when the axle gets put into bind it allows the axle to move however much it needs (sometimes up to 1″). It acts like a solid link when it needs to be, as much as it is flexible when the situation requires as well.

5.)How many man hours does it take to build one set of Carli radius arms, start to finish?

One set of radius arms alone require 8 hours of welding and another 2-3 hours for assembly and crating. Those times do not reflect the other parts that are required in the 6″ Systems, like the Radius Arm Drops, Crossmembers, Bump Stop Drops, Track Bar Drops, etc. One complete kit, when laid out in its raw laser cut form, will take up approximately 35 square feet of space, more real estate than a 4’x8′ sheet of plywood.

To check what kinds of kits and components Carli Suspension has for your truck, CLICK HERE.

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