2009-201x Dodge Ram pickup trucks - suspension, steering, and wheels
Ram trucks built starting in 2009 used a multi-link coil-spring rear suspension for better ride and handling. The coil-spring setup centralized and absorbed bumps and impacts, while reducing friction; it also weighed 40 pounds less than a leaf-spring configuration. For the 4x4, the Ram had a larger articulation range than its leaf-spring competitors, with less freeway hop. (Coil-spring setups are commonly used in heavy-duty applications such as semi trailers and railroad cars.)
Shock absorbers were forward-facing and positioned on the outside of the frame for optimum damping. Shocks were tuned for optimum balance in order to reduce ride harshness and provided more of an absorbent feel. Power-assisted rack-and-pinion steering was standard; wheels ran from a 17-inch stamped steel (ST) to 20 inch aluminum (optional on SLT, Sport, and Laramie), while a full sized spare was standard across the board.
Steve Williams, Senior Manager of the body-on-frame product team, on the 2009 Dodge Ram suspension
What is the design purpose for the rear sway bar to be mounted facing rearward?
S.Williams: Primarily, it was a packaging concern.
What about frame rigidity? Would it be stronger with the attachment point ahead of the rear axle?
Williams: That was addressed early in the design phase. The only room for the bar was behind the axle, so the frame was a clean sheet design to accompany this. The frame is a box section, hydroformed to provide the strength required.
The old GM coil sprung pickup of the 1970s was known for poor handling loaded, and excessive wheelhop on acceleration when unloaded. How were these problems addressed?
Williams: The GM system was a three point suspension. The Ram's suspension is multi link that controls the motion of the rear axle. The spring placement helps to control wheelhop under accelaration.
Allpar: There was mention of a diesel for the light truck, Any hints as to size and configuration?
Williams: All I can say is that it will be a "V" design....you can speculate further if you wish. [Allpar note: this appears to have been pushed back at least two years.]
Allpar: How much consumer input was involved in the redesign?
Williams: We visit Allpar and other sites, read opinions of our products, and take that into consideration when designing the entire vehicle.
Allpar: There is a hybrid system in Rams' future. Is it the same system as the Aspen's?
Williams: Essentially, yes, but reprogrammed for the unique needs of the Ram truck.
Bob Sheaves, independent suspension engineer, on the new Ram suspension
Overall, I am impressed with the efforts of the
suspension design engineers and development engineers on the new rear suspension of the Ram pickup. Building on the success of the original ZJ Jeep (Grand Cherokee) rear link-coil suspension design, it appears that many of the shortcomings of the original ZJ design have been corrected.
The new spring layout shows the attention to details and vehicle dynamics that the people at "JTE" [Jeep-Truck Engineering] are famous for. While odd looking with its offset springs to the layman, this design shows attention to the fundamentals of vehicle dynamics.
In 1967, GM used a 3 link (as opposed to the new Ram's 5 link) coil sprung suspension. The result was that the vehicle had a very comfortable ride when empty (industry leading, in fact), but when any load was placed in the pickup bed, the vehicle became unstable and sloppy handling. This result almost sank the new trucks before they were even out of the gate (it was deleted in favor of a conventional Hotchkiss shortly thereafter). The new Ram is the first U.S. volume built pickup truck since that time to attempt to use coil springs as its primary suspension system.
The pitch of the springs shown in the accompanying graphic show how the springs are canted and "bent" at the BPL position (BPL=Body Part Loaded- this means a loading of 2 each 150 lb passengers, full fluids, and 1/2 payload all combined to be the base point of design for the vehicle) to allow the reactions to motion of the ground contact patch ("where the rubber meets the road", to use an old marketing phrase of another company) to be efficiently controlled and isolated from disturbing the ride quality and stability of the vehicle.
The UCA (Upper Control Arm) links appear to be splayed outward at the frame attachment points, providing a lateral stability to the system that, in conjunction with the track bar (or "panhard rod") keeps the lateral shift of the axle, between jounce and rebound (maximum travel up and maximum travel down- NOT "bounce" and "droop"), to the minimum arc possible. Due to the over-constrained system (more about this in a moment) the axle will travel laterally in the vehicle, through an arc of approximately 2" total, left to right. The positioning of the track bar ensures that the travel will also be split evenly from jounce to rebound, minimizing the dreaded "head toss" so prevalent in the Jeep XJ (Cherokee SUV), MJ (Comanche pickup), and early ZJs.
The side view angularity between the UCA and LCA (Lower Control Arm) indicates a long instant center, a theoretical point in space ahead of the axle, that controls the fore and aft arc the axle travels through as it goes from jounce to rebound. By having a long instant center, you ensure the axle does not change the wheelbase a great deal, affecting braking distances and geometry and upsetting the transient dynamics of handling in an emergency lane change.
The rear stabilizer bar is the only complaint I have about this design. As was shown on the original Dodge Dakota 4x4, the most effective position of a stabilizer bar is to place the end links as close to a rigid body (meaning the center of the frame where the bend and torsion is minimized) as possible. I do not know all the compromises the engineering staff were forced to make, but I am concerned this location has forced several poor tradeoffs, primarily excess weight needed from larger than desired components to control the loading the vehicle sees.