Ever notice how full suspension mountain bikes have a curve in the downtube by the fork? This design is to ensure the fork never impacts the downtube, but it also negatively affects the downtube stiffness. A straight down tube, on the other hand, produces a stiffer frame with the best strength-to-weight ratio. This means you get a better riding bike without any weight penalty. Trek Engineers developed Knock Block to remove the design constraint caused by fork clearance, allowing a straight downtube. Knock Block is an integrated, redundant frame protection system so you never have to worry about self-inflicted scuffs, dents, or cracks from spinning handlebars. It’s a system consisting of a special stem, headset topcap, spacer, and chip in the frame. It starts with a “stop chip” in the frame near the headtube. The stop chip limits the turning range of the custom keyed headset cover. The top of the headset cover has notches that lock into corresponding notches on the headset spacers. These also correspond with notches in the stem, for the strongest connection to the steerer tube. Working together, these parts will prevent the fork crown and handlebar controls from hitting the frame. For additional, fail-safe protection, we’ve also added an impact-absorbing rubber down tube bumper. With Knock Block – you get integrated frame defense, allowing Trek to use a straight down tube for a lighter, stiffer frame. The result is a better riding bike that you can push harder with more peace of mind.