Like just about everything else once dismissed as silly kid stuff, go-karts have raced into the mainstream of grown-up extreme sports. The F1 Race Factory, bordering the Tempe gateway just south of 48th Street and Washington, requires a valid driver's license to race its modified European karts -- each outfitted with a speedy Honda GX 270cc motor and Yokohama racing slicks -- and serves beer and wine in its Trackside Grill (although tipsy karters are subject to Breathalyzer tests). Plugged in to the Valley's import racing subculture, F1 has hosted Saturday night "Show Your Sh*t!" car shows in its parking lot and has lately become a favorite training ground for the drifting crowd. Regulars consider driving the low-down karts as the purest form of racing -- as close as you can get to feeling every twist and turn on the track without having to peel yourself off it.