Most people who own a heavy-duty pickup know what it's like to live a life of compromise. You purchased a three-quarter- or one-ton truck because you need the load-carrying capacity. But with the extreme GVWR comes a heavy-duty ride quality-or lack thereof-often accompanied by reduced vehicle control created by rear axle bounce. And did we mention axle wrap under acceleration and braking? That's just the way it is.

The engineering teams at Firestone Industrial Products and Sanluis Rassini felt they could find a solution with a new rear suspension system that tilted the compromise in favor of the end user. Firestone is known for its Ride-Rite air spring technology, which delivers additional load-carrying and load-leveling capability. Sanluis Rassini engineers and manufactures 96 percent of the leaf springs used in new vehicles in the U.S., bringing a slew of OEM-level design and testing tools to the joint program.

The two companies worked together to develop and patent the R4Tech hybrid air- and leaf-spring rear-suspension system. This new system gives customers improved ride quality and handling when the truck is loaded and unloaded. Additionally, it minimizes a counter-steering characteristic of a leaf-spring suspension that causes the rear axle to steer to the outside of a curve when there is a body line that compresses the suspension on one side and extends it on the other. The system also incorporates a kneeling feature that allows the rear of the truck to drop between 3 and 5 inches to facilitate loading the bed or connecting a trailer. Finally, the system keeps the rear of the truck at a ride height you can set, even as you add weight all the way up to the truck's factory-rated load-carrying capacity.

The R4Tech system replaces the massive factory spring pack with a leaf spring whose primary job is to locate the rear axle. A pair of Firestone air springs takes on the load-carrying responsibility. One significant advantage of loading the air springs is that the effective spring rate is variable, which means improved ride quality loaded and unloaded. As more weight is added, air pressure is increased and the spring rate goes up as needed, but it's still less than those of the original leaf springs. One of the key goals with the R4Tech system was to deliver a better ride quality than stock, regardless of the load in the truck.

A height-control adjust valve moderates the pressure in the air springs to keep the truck at the desired ride height. To control axle wrap, a J-link is added under the front section of the leaf spring. This maintains the distance between the axle and leading leaf spring mount, incorporating a rubber pad that contacts the main leaf under hard acceleration. The last component in the system is a pair of Ride-Rite LS tritube mono-flow shock absorbers. The valving in these shocks is automatically adjusted for greater control as weight is added to the truck.