Advanced Suspension Systems
At a bicycle trade show in the early 1990s, an engineer for Schwinn predicted all bicycles sold by the year 2000 would have suspension built into them. Most people who heard him were skeptical, at best. Time has proven him far more right than wrong. It is now 2004, and virtually all adult mountain, hybrid and comfort bikes, as well as some road bikes, contain active suspension components.
Active suspension parts (pieces that have pivoting or sliding components to provide flex) continue to evolve at a rapid pace. The "Holy Grail" for the active suspension bike is a design which absorbs all bumps and vibrations without absorbing the rider's pedaling energy. The industry is getting very close, if it isn't already there, to this elusive goal.
The most advanced design so far comes from a collaboration between Specialized bikes and Fox Racing Shox. In 2003, Specialized introduced their "Epic" full suspension mountain bike to rave review and great racing success. In fact, the 2003 men's ATB world champion rode an Epic; it was the first time that the championship was won on a full suspension bicycle. What makes the Epic design unique is its "Brain" suspension which uses an inertia valve to lock out the shock against pedaling forces while responding to bumps when needed. The rear shock uses an air spring in combination with an oil dampening system controlled by an inertia valve.
Translation? The oil in shocks is used to "dampen" the air or coil spring. Dampening keeps the shock from behaving like a pogo stick, bouncing all over the place. When the spring is compressed by a bump, it wants to spring back quickly. The oil in the shock is there to retard that quick reaction. This slowing of the spring is achieved by having the oil flow in a restricted manner, back and forth inside the shock. A valve controls how fast the oil can flow and thus controls how fast, or slow, the shock returns to its unsprung position.
On the Specialized Epic, the rear Brain shock uses an inertia valve. That valve is opened and closed by a brass cylinder that blocks the oil flow, unless a sharp bump moves the cylinder out of the way of the valve opening. When the oil is blocked by the cylinder, the shock will not give and the rear suspension will not move, giving the bike an efficient, "hardtail firm" ride. This is because the relative slowness of pedaling forces will not affect the shock quickly enough to move the cylinder in order for oil flow within the shock.
If the rear wheel hits a bump, however, the quickness of that motion will move the cylinder, opening the oil valve and allowing the shock to give and the rear wheel to float over the bump. This all happens in a fraction of a second. The resulting system is responsive to terrain input (bumps) but not to rider input (you, pedaling the bike) until the going gets bumpy. You have to ride it to believe it. Come in for a test ride soon.