https://www.youtube.com/watch?v=j-uM...nel=TheCarizon
Do you have divorced coilovers?
I'm sure some suspension guru will come and give a perfect answer but.
Afaik. You can't do anything to the spring to change stiffness. You can adjust ride height and preload. Neither of which will change the stiffness of your spring.
You can buy stiffer springs tho.
In the video he shows raising ride height on divorced spring setup for bc coilover.
good video to explain how right height/preload don't affect stiffness
https://www.youtube.com/watch?v=eRJ9...=Flyin%27Miata