from this thread
http://mazdamp3.com/vbb230/showthread.php?s=&threadid=22716&highlight=spring+rates
The Numbers
When compared to the Racing Beat Springs that originally come on the MP3, the S-Tech's are very soft. Unfortunately, I haven't been able to find out the exact spring rates of the MP3, but through searching on the boards and making a few phone calls to Racing Beat I found the numbers I've listed below. We all know that the MP3 springs are 27% stiffer than the regular Protege Spring Rates. The regular protege rates are listed at 169ft lb. front and 119ft lb. rear. That translates into 215ft lb. front for the 152lb ft. rear for the MP3. The S-Tech's are 179lb ft. in front and 145lb ft. rear. So....if the MP3 came with the factory protege springs, then everything would be perfect. You'd have a nice rate increase when upgrading to the Teins, but using the S-Tech's for the MP3 is actually a step down in stiffness. This may be nice for some, but it is not what I was looking for.