yeah, chris I keep adding weight to my cars too for outdoor racing. I sometimes think I need an outdoor packs and a shorty for indoors. The car always felt a little sluggish indoor with a full pack. But I spend 95% of my time outdoors. you can add weight in the tray to get the right feel, but the shorty will put less "power", so I am of thought, that if you need more than just a few grams of weight, the full pack might be best, even in 17.5