The difference between a parabolic spring set, and a normal spring set, is that the parabolic springs are spaced apart and can work individually. A normal spring set requires all springs to move, (more or less) in unison, whereas with a parabolic spring set, the springs are able to work individually, so to speak.
As a result of this the parabolic spring set is usually lighter as it has less leaf spring.
Attached are two pictures of our truck. one picture shows the rear ATW parabolic spring sets, the original rear dual wheels are still attached. The other picture is from the right rear looking forward and towards the left rear spring set. You can see the air gap between the leaf springs. The third picture is one of our 17" wheels.
Parabolic spring sets are lighter as there are fewer springs, we have three leaf springs on the front, two sets of three leaf springs on the rear.
You don't mention if you are going to super single wheels? There is a difference between super single wheel rim sizes, the difference between the 19½" and 17" rims and your choice of tyre does make more of a difference than I would have thought. We have the 17" wheel option.
I have hopped directly from our truck into another Isuzu NPS 300 fitted with 19.5" super singles running quite reduced air pressure on a corrugated dirt road. The 19.5" wheel/tyre combination, which were Toyo tyres on the other NPS was very noticeable in lower ride quality compared to our NPS. His NPS also had the ATW full suspension change, so it was a reasonably close apples to apples comparison.
I couldn't wait to get back into our truck, while the owner of the other truck had one question; how much are those 17" super singles?
I hope this helps.
