Originally Posted by HP Autowerks
TC has been doing this for 20+ years, both in suspension development and racing. He offers suspension kits for M cars dating back to the E30 all the way to the late E9x. The spring design you are referring to might be the E36/E46 barrel style springs for increase stroke/travel, his E9x springs are constant ID linear rate.
I like what TC Kline does because he doesn't just re-hash the same system over and over if it doesn't apply. The rear spring is an example. Which is the exact reason why I am not a fan of KWs.
I really like my TCKline D/A and really don't see the need to step up to something more expensive for my purposes. If I wanted to get every possible second I could because I wanted to be DE king or win a race, then maybe I would get something more.