Hi there, string tension is 47-62 pounds (G-to-E), whereas Spiro Weichs are 62-67 pounds, so they are even lower tension - link here [url="http://baen.tamu.edu/users/rel/personal/BassStrings.html"]http://baen.tamu.edu...assStrings.html[/url]
Feel wise they are chalk and cheese as Spiro Weichs are relatively slim steels, whereas these are fat chunky gut-alikes.
Bottom line: If you want to emulate an old school gut sound these are a stress-free (stable tuning) and maintenance-free (no clipping hairs or oiling)alternative. If you want precision and growl, I would stick with Spiros. Hope that helps!