I contacted our local automotive spring company. They can produce custom springs, access a wide range of aftermarket springs, access factory springs from the automotive mfg's. They also have the load specs for the factory springs.
Here is a bit of information on our 2009 R/T C190V: The Chevy factory leaf springs, as delivered to Roadtrek are part number 25756366
. This number has been superseded by 20905750
. Both of these springs are rated at 2485 pounds/each. The max axle load for a pair of these springs is then 4970 pounds.
The weight of the Roadtrek C190V, with water in the tanks is over 5000 pounds on the rear axle; and with a typical load of traveling gear, is 5400+ pounds on the rear axle (before towing anything). These leaf springs are overloaded
To some of us, this is made obvious, by seeing the main leaf springs resting on the thick, bottom rebound (overload) spring. Booster
and others have added air bags, and add pressure until the rebound/overload leaf has some clearance. They report that this also provides a ride that is less harsh at the rear axle.
In this view, you can only see the forward end of the rebound leaf (arrow).
Passenger side view of rear axle/brakes/leaf spring.
There is a small gap between the leaves, because there are thin spacers between the leaves, and a rubber pad at the tip of the rebound leaf (arrow).
During normal use, the upper leaves should not be resting on the rebound leaf (on the rubber pad at the end of the rebound leaf). This condition is for the occasional "extra" load, of a 1 ton work van.
When I spoke with the Chevrolet Parts department, they suggested the spring designed for their 10,000 GVW van, part number 22799639.
When I spoke with our local spring dealer, he suggested the aftermarket spring #22-1175. This is a "Full Taper" leaf spring, that is rated for 3710 pound per spring, or 7420 pounds per axle. With these springs, the 5400 pound weight of the van would be only 73% of the max load of the springs. This is an excellent "normal" load for this spring. Also, the "Full Taper" springs move easier and don't normally need a rebound/overload leaf. The #22-1175 has 3 leaves (3710 pound), and the 22-1175HD had 4 leaves (4960 pounds). I think the HD would be too much spring (twice the factory spring load), and would be too stiff.
With the 22-1175, I would not need the 4" lift blocks, currently installed, and could drop down to a 1" block, or less. This will also provide for a smoother ride, with less harshness at the rear axle.
Note: The "Full Taper" springs are shaped like the rebound/overload spring in the photographs above. They are thick in the middle, and get thinner as they get close to the tips. The main leaf and all the lower leaves are 60" long. They do not get shorter, as you move down the stack, like a typical leaf pack. Each leaf has a thick spacer at the tips, and makes no contact with the upper leaf, except in the middle and tips. This system has less friction, and is reported to act much like a coil spring.
We will see.