I might be on to something here… the rear springs in my plug-in definetly has less flex than the springs on a non plug-in.
Update: "Plug-in springs are slightly stiffer and will result in approximately .25” more ride height when used on a non plug-in Prius as well as slightly more carrying capacity with reduced sag from the weight. Springs are interchangeable without any other modifications. If carrying capacity is your goal you would still be much better off going with an air bag in the rear, and for less money than the plug in springs would cost." -PriusOffRoad
After installing spring spacers on two different Toyota Prius’s, my arm muscles can testify that there is a significant difference in the rear springs and how must flex… or traveling area because my plug-in springs took longer to install the spring spacers than a non plug-in because the non plug-in springs were tremendously more flexible than the springs in a plug-in.
In fact, they have separate part numbers and associated pricing points.
I’m working with a dealership local to me, goal is to compare the springs side by side for any noticeable visible differences. From there, I’ll find out what makes the springs different from each other.
I even tried to find them on Amazon since they have good return and the Plug-in Springs are out of stock!