Technically, you are allowed to wear a skirt on TRON Lightcycle / Run at Magic Kingdom, but it is not recommended for practical reasons. The ride vehicle is designed like a motorcycle; you must "mount" the bike by swinging your leg over the seat and leaning forward into a "tucked" position. This posture can make wearing a short or tight skirt extremely difficult and potentially revealing for those in the loading area or the row behind you. If you are committed to the look, many Disney "pro-travelers" suggest wearing biker shorts underneath or requesting the "accessible" car at the back of some trains, which features a standard upright seat and lap bar rather than the bicycle-style straddle. For the best experience without a "wardrobe malfunction," opting for leggings or shorts is the generally accepted standard for the Grid.