Racing downhill at high speeds over rough and twisting terrain requires a special bike. Having the technique to ride like this is essential, but only a bike that can absorb large impacts at speed and stay in contact with the ground will allows a rider’s skill to be used to maximum effect.
Heavy-duty, reactive, and supple full suspension is what marks out the downhill bike. This means suspension with plenty of travel, but also plenty of control. It is pointless if the suspension absorbs a major jolt but then springs back just as severely. Sophisticated damping controls this springing, as do other features that keep the suspension in contact with the ground and reacting to it.
The downhill bike is similar to a track bike in that it can only be used in the application which it was designed. Because of the safety margin built into each component, downhill bikes are so specialised and heavy that riders have to push them or take a ski lift, to get back to the top of a run.