The stock msport strut - and its Bilstein and Sachs OEM style aftermarket equivalents - is the recommended replacement for customers who simply want to refresh their suspension back to factory new. They also work great with a mild lowering spring, like Eibach or Dinan. In fact, Eibach and Dinan tests their springs with factory dampers, so you know that they match up is fine.
The Bilstein B8 is the go-to strut for most high-performance applications. Quality is extremely high and their technology - without going into details - sets them apart. We strongly recommend them for most applications where a customer wants to lower their vehicle. They are a firm shock - maybe even firmer than a stock M3. There is obviously some trade off between performance/handling and comfort, but that is always the case when you want superior handling. Most people will find them perfectly acceptable for daily driving unless perhaps you like comfort and live where the roads are horrible. We've used B8s on most of our personal cars and love them. Well, sometimes the wife doesn't :-)
Now look at the one in the middle. It is the BMW MPerformance strut. No, it is not the same as the msport. There are big differences. First, the MPerformance strut is significantly firmer than the msport. It is closer to the B8 in dampening, and has all of the same great performance/handling benefits of a firmer strut. But look closer... you can see that it is shorter than the msport strut and B8. It is exactly 1/2" shorter than both, which is because BMW made it to match their MPerformance springs, which are also 1/2" shorter than stock. Talk about attention to detail! Because of this precision, we used the MPerformance strut and springs on our shop car and LOVE them! This set up fits perfectly in between the msport and B8 for comfort, performance, and handling.
This is why we are announcing that we now have a new option for our RWD F3x customers: Our SM70X series kits will use BMW MPerformance struts and shocks with any lowering spring that you choose - Eibach, H&R, Dinan, or MPerformance!
Like all of our kits, our SM700X kits will come fully-assembled and 100% complete. No spring compressors or special BMW tools needed. Just open box and install.
Give us a shout!