Does anyone know if the STR springs are linear or progressive?

 

I would have to say progressive or at least the eibach and H&R are.

You can tell because the coil spacing on the springs.

 

thanks!

 

progressive-small coil spacing on the ends, larger spacing in the middle. the more weight on them the stiffer they become. As weight goes up so does the spring rate.
The higher the spring rate the stiffer the coil.

Linear-equal spacing through out the coil. retention of the spring rate through the weight range. as weight goes up springe rate remains relatively the same.