The Rocky Mountain Vertex RSL 70 2009 Mountain Bike. When Rocky Mountain first started building bikes it quickly became apparent that traditional frame geometry wasn't going to cut it on the steep descents and tight turning singletrack of southern British Columbia. To help tame this rugged landscape they developed ST3 Geometry - or Sloping Top Tube Technology. A sloping top tube means increased frame stiffness and strength, and when things aren't going so well, more stand over height for crucial dismounting ease.The frame layout creates a compact front end, giving increased agility in tight turning singletrack while providing increased stiffness for greater control in all conditions. It's also bomber construction: with a greater separation between the top tube/seat tube and seat tube/seat stay welds, frame stress is distributed over a larger area of the seat tube. Originated by Rocky Mountain and copied by others, ST3 delivers a better handling, stronger frame - the ride of a lifetime.