So I scoured online forums. They're a great resource for discovering the ins and outs of part applications and their effects on performance. Sure enough, bits and pieces collected at my cubicle. A set of 18-by-9-inch Advan Racing GT forged aluminum wheels ($829 per wheel; +35mm offset) from Mackin Industries were first, followed by a KW Suspension Clubsport 2-Way Coilover kit ($4,000). The Advan GT's are newish to the American market, were engineered using motorsport knowhow (they're forged by Rays Engineering and have tech such as anti-slip knurling), and have a definitive racy attitude.

2015 Subaru WRX STI Launch Edition AutoFashion USA Elroy KW springs

They're a slight step up in size from the stock BBS wheels — a half-inch wider and flusher to the wheelwell's outer edge because of the lower offset — and required no body modifications to fit. The KW's are born and raised on the Nürburgring. Need I say more? They're sporty enough for the track yet compliant enough for street use. Beyond the ability to adjust height, both rebound and compression can be tuned to a user's liking.

2015 Subaru WRX STI Launch Edition Advan GT wheels

Instead of replacing the entire braking system, I opted to swap the stock rotors with more performance-astute high-carbon, cast-iron versions made by Brembo, Subaru's chosen brake supplier. The 326mm front ($481 per set) and 316mm rear ($480 per set) slotted rotors are said to dissipate heat better, given their intricate ventilated design. The front four-piston calipers bite on a more aggressive set of Project Mu B-Force pads ($188); the stock pads remain inside the rear two-piston calipers.

I next added a set of track-ready 245/40R18 Dunlop Direzza ZII Star Spec tires ($225 each) and Tire Sticker sidewall decals ($25 per set). The ZII Star Specs have been a top choice among the track-day crowds in Japan for their gummy compound. Other reasons for trying the Dunlops: their JDM (Japanese Domestic Market) roots and because a racing version is used in non-Subaru's 24H Challenge car. (Stay tuned. I'll be trying out Bridgestone's new RE-71R rubber, too.)

Autofashion USA in San Diego took care of all the parts' installation and tuning. So far, after about a thousand miles of street driving, everything has worn in nicely. No jittering and no odd noises. The ride is tauter (the dampers were set to their stiffest settings), and the brakes feel more resistant to fade. My sole gripe relates to the Dunlops' noisiness. Their grip is substantial, but so too is their droning. After an alignment, it'll be time for some serious driving and instrumented testing. Can't wait!