On a full size bypass shock, it is essentially multi stage damping based on the position of the piston, eg a triple bypass has 3 damping zones.
Your first zone generally is very lightly valved so its nice and supple over small bumps and imperfections. Another way to put it...slow speed damping.
The second zone is moderately valved. Vehicle speed has increased and that piston will float in this second zone most of the time. When its in this zone, it bypasses the first zone (where the name comes from)
Third zone is heavily valved. Large whoops, jumps and G outs will get a vehicle traveling at speed into this zone. Idea being that the damping slows down the shock piston velocity enough to minimize the chance of shock bottom out, supplemented with hydraulic bump stops. First two zones are bypassed.
To date, I have not seen an RC shock that performs the same functions as a true bypass and its not really the same as a "dual rate" piston that has been done in RC before. Any time you see people running a second shocks its usually for looks or performs some additional damping to the primary coilover.
*Sorry for slight thread jack:roll:
*Spring rate determines ride height, not damping
**Except if your shocks are hydrolocked...pogo stick!
