Like many of you, I purchased my '15 FiST while shopping for a FoST. To me, the car was just more fun to drive and cheaper at that. After owning the car for about a month I started experiencing lower back pain and I had no idea what was causing it. It wasn't until about month 2 that I realized that it was the rough suspension mixed with the lovely Southern California roads. I started looking into fixes and came across forums saying that the over dampened rear shocks were the main culprit to the rough ride. To counter this I ordered and installed Koni STR (orange) rear shocks and I noticed an immediate softening during my daily commute. However, there was a tremendous amount of squat in the rear when accelerating; something had to be done. To counter this effect, I installed a set of Vogtland lowering springs and that got rid of the rear squat, but the search was not over yet. The car still had a lot of roll when making turns, so I did some more research. I was looking into purchasing aftermarket sway bars and I was almost ready to pull the trigger. Then, I noticed folks talking about rear torsion bars and how much they reduced body roll. I settled on the TB Performance torsion bar and installed it in about 10 minutes (the rear suspension is ridiculously easy to work on) and I have to say that this car handles amazing now. Body roll was reduced by around 75% and every turn induces uncontrolled smiling. Yes, the TB Performance torsion bar was the icing on the cake and now I am completely satisfied with my daily commute, for now. If your FiST is killing your back or you would like to use your touchscreen on the freeway, I highly recommend these mods. However, the TB Performance torsion bar is a must for any driver.