As far as the BC Racing ER series vs the KWv3 coilovers....
I agree with Mikey. Now after driving both sets of coilovers both on a 370Z..... I am once again as impressed if not more so with the BC ER series coilovers.
I too, am a distributor of both BC and KW and also make more money selling the KW's. So what I am saying is unbiased from a $ standpoint.
Also the great attention to detail and top level of customer service from BC Racing North America helps out a bunch too (compared to KW)
With Relentless Autosports being a top tier authorized distributor, I am able to tailor design the spring rate and shock valving to each individual. We at RA also have a custom spec'd BC line of coilovers available that come with custom compression and rebound valving as well as the ultra light swift springs Similor to what Robert does with his RobiSPEC stuff
.
I personally do, and have done a lot of R&D for several different suspension, tire, and chassis companies.
I am also the guy that BC hires to drive their winning and record setting Time Attack cars.
So just to summarize. I feel that both KW and BC Racing are both viable options, it just depends on your individule needs, and budgets. Just don't always believe the forum hype on a more expensive product.