Ram Truck unveiled new chassis cab heavy-duty work truck models at the Chicago Auto Show in February. With towing maxing at over 35,000 pounds, it's clear that something is happening with these trucks. Now we've had a chance to get up close and learn that the secret is in chassis engineering.
The similarities between the consumer-grade half-ton Ram 1500 pickups and their heavy duty siblings are clear. Even the work truck versions unveiled in Chicago have a lot of similarities. Yet those are mainly on the surface. Removing the bodywork and interiors shows that the Ram 1500 and the heavier 3500/4500/5500 trucks are very different.
Traditionally, the numbers denoting a work truck's vehicle class (aka "capability") are divided into four groups in the United States. A Class 2 vehicle is anything with a gross vehicle weight rating (GVWR) at or under 10,000 pounds, often referred to as a "2500" or "three-quarter ton" truck or van. A Class 3 (3500) is at or under 14,000 pounds, a Class 4 at or under 16,000 pounds, and a Class 5 at or under 19,500 pounds. The Ram chassis we'll be discussing here are inside the Class 3 to 5 categories.
Most of the secret to the maximum 35,220-pound (15,975 kilogram) towing capacity and 12,510-pound (5,674 kg) maximum cargo capacity in the new Ram heavy duty chassis trucks is in the framing. The new chassis is based on a frame made up almost entirely (97 percent) of high-strength steels. The C-channel rear frame rails use 50,000 psi steel and have eight separate roll-formed cross members. This means a highly rigid yet light weight frame.
Ram's new design for the heavy duty chassis cab framing includes a hydroformed front rail section with a wide frame rail width to accommodate outboard positioning of the suspension springs to improve roll stiffness. Ram says this improves both the ride quality and weight carrying capacity of the truck's front track, aiding stability in the process. On the 3500-class truck, a long-weld cross member adds stiffness without requiring more reinforcement. The other trucks have a more traditional multi-point front section.
Ram heavy duty commercial trucks also have other design elements made to allow aftermarket and specialty add-ons for equipment easier. All items in the truck's components behind the cab are kept below the top of the frame rails, which are themselves pre-drilled with mounting holes and set with the upper portion of the "C" flat and level. Dual fuel tanks are available on all models, also positioned below the railing, and fuel fillers and channels are kept inside the framing for that same purpose. The dual tanks are self-leveling, requiring no operator switch to swap tanks as one empties.
The suspension on the 2019 Ram chassis cab models works in concert with the framing. A three-link coil sprung front suspension on the 3500 is designed for heavy loads, positioned with two frame-to-axle radius arms and a 35mm stabilizer bar. A five-link coil is attached to a beam axle for increased capability commensurate with the 4500 and 5500 models. Front shock absorption on the trucks consists of gas-charged pistons with built-in rebound travel stops, tuned to the chassis cab truck's wheelbase, powertrain, and capability. The 4500 and 5500 models can be outfitted with higher-capacity springs for forward-biased weights in upfit applications, like aerial booms or snow plows.
The suspension at the rear of the heavy-duty chassis on these Ram trucks consists of traditional leaf springs designed for the various weights the trucks are capable of. The heavier the truck's capabilities, the larger these springs become, accommodating up to the maximum tow/haul of 35,220 pounds and 43,000 pounds of gross vehicle combined weight.
Steering on the Ram HD chassis is based on a recirculating-ball steering gear and robust linkages. Large-diameter drag and cross-vehicle links (29 mm and 51 mm respectively) hold steering characteristics no matter the load on the front end. This limits the amount of effort required while maintaining load capability. Wheel alignment is dimensionally-controlled through steering knuckle caster and camber settings.
Finally, to stop all the expected weight, the brakes were reconsidered for better capability. Disc brakes with hydro boosting are standard on all 3500-class and higher Ram trucks. This system offers better stopping distances and over-matches the highest capability of the given truck. Front rotors are 14.17 inches (360 mm) on the 3500 and use dual-piston calipers. The rear rotors are 14.09 inches (358 mm) with similar calipers. The 4500 and 5500 models have 15.35-inch (390 mm) front and rear rotors with similar dual-piston calipers.
Outside of the chassis, the new ram HD trucks have some powertrain upgrades. The base engine is a 6.4-liter Hemi V8 gasoline engine with an eight-speed automatic transmission as standard. This engine is not new to the Ram lineup and delivers 410 horsepower (306 kW) and 429 pound-feet (582 Nm) of torque in the 3500 model. The same engine is tuned to output 370 hp (276 kW) and the same 429 pound-feet on the 4500 and 5500 models.
A newly-updated Cummins 6.7-liter turbodiesel engine is optional in the Ram HD chassis trucks. This engine runs to an Aisin six-speed automatic transmission with optional PTO, tuned to handle the Cummins engine's 360 horsepower (268 kW) and massive 800 pound-feet (1,085 Nm) of maximum torque. The new engine has a cylinder block made of compacted graphite iron for better strength and vibration dampening, reducing the engine's weight by about 60 pounds. A cast-iron cylinder head has revised exhaust valves and springs and new rocker arms driven by a hollow camshaft. New oil and water pumps finish the upgrades for better efficiency and further weight savings.
Also new on Ram HD chassis work truck models are advanced safety and driver aid technologies such as adaptive cruise control, forward crash mitigation (with automatic braking, including automatic trailer braking), and others.
There's a lot going on with a work truck's chassis design and the new Ram heavy duty chassis trucks are a good reminder that numbers can matter.
Product Page: 2019 Ram Heavy Duty Chassis Cab
Ed's note: The original text of this article erroneously referred to a "hollow crankshaft". The text has been corrected and now reads "hollow camshaft". Our apologies for this error.
