If you intend to use the car for track events with larger than std. tires and/or R compound type tires, the subframe mod is a must to assure alignment under high load cornering. It also acts somewhat to improve traction (like traction bars) because the links are noncompliant compared to the stock parts. I did not use the RennTech kit because I did not like the idea that you had to 1) remove the subframe from the car to do the installation and 2) that you have to drill out the mounting points. Making it a truely permanent change. I engineered a similar kit using higher quality components than that offered by RT. I have found it to be the single best improvement to track handling because it allows complete adjustment of the alignment and maintains the settings at all times. I also use a RT front bar (strongly recommended). My car is lowered with 255 fronts and 285 rears.