Sway bars are the 3rd major mod that I have put on my 2009 STi hatch. The first being an AP, the second, an Invidia divorced catted DP, and now sways. (The car came with a Type One Racing sparrow cutback (thank you previous owner!)). If I had to rank the changes I have made so far, they would go 1) AP, 2) Sways, and 3) DP. These cars are touted as high performance cars, which they definitely are, but as we come to find out, they lack a certain "edge" out of the factory. One of these edges is the understeer so many people talk about. After reading thread upon thread on different sites it sounded like sways were more than worth the expense as a "bang for you buck" mod. This mod has been on my wish list for quite some time and a deal came up that I couldn't pass up. So, three weeks ago I bought them and two weeks ago, I installed them. Here are some pictures of the difference in size. RCE's website has their size listed as 25mm hollow bars.http://www.racecompengineering.com/...rs/racecomp-engineering-gh-sway-bars-265.html Front: Rear: Wow, what a difference these make!! These particular bars come with two settings, basically soft and hard. I installed both the front and rear at the hard setting. Thinking back to the comment of "performance car", these took a big step in that direction and make me wonder why Subaru would not make this adjustment in the first place. The way the car "attacks" corners now is very exhilarating. The car now feels like it wants to be there in the corners. It also adds to Subaru's mantra of "confidence in motion". The car is much flatter and and the steering actually feels more responsive to me. Even, though I got these bars at a discounted rate, I would highly recommend this upgrade to anyone, as they were a noticeable enough difference from stock for me. I plan on tracking the car a couple of times this year (first one in May at AMP if anyone is interested , so I hope to see and feel the difference out there too. I was at that track twice last year, so it should be a pretty good comparison. Coming from a 4Runner before this car, everything is more fun for me, but hopefully this helps anyone considering this mod.