Actually not so, 'good shocks' can have diff valving for compression (hits) vs rebound but ALL shocks 'dampen' the action of the springing in BOTH directions.
Some 'good' shocks have both preload and some can have pre-load adjusted as well as how hard or easy the 'valves' will open to allow more oil/fluid inside to flow.
** a 'closed' valve does not allow oil/fluid to flow and causes 'harshness' or restricted movement of suspension - thus valving is the most important aspect of the typ simple mh shock, open valve obviously allows fluid flow but also can have multiple orifices for fluid to flow and valving can open them in a progressive manner - so valving can be fairly complex just in itself.
They can also have rebound tuning as well, but a PURPOSE designed shock will be 'tuned' in both compression and rebound for the 'loads & speed' of compression and rebound of the mechanical parts of suspension.
So a 'good' tuned shock both 'smooths' compression AND rebound and 'should' make for a better and smoother ride - but essentially they are to absorb the harshness of an uncompensated mechanical spring which has ZERO dampening generally.
Check out either racing shocks or just off shelf off road motorcycles for the sophistication that shocks can have, it is a science all in itself !
PLUS, you CAN buy shocks with aux springs so they can have an even greater effect on suspension tuning, but simple Bilstein and Kona shocks, it is up to the 'engineering' (if any) of the engineers/tuners, but do not expect too much and NO tuning at all.
Just to give info, shocks from OTHER uses (from a catalog) can be used on mh, but you must know the total max and min lengths of travel, as well as springing amounts & weight of vehicle involved - just so to NOT destroy or hurt things if trying for some tunable shocks - non trivial stuff - but could be very rewarding - and we have just been talking about simple UP&DOWN suspension movements, no dynamics of side-to-side, etc !!
Originally Posted by edgray
I think Sumo “springs” are likely to provide more relief from jarring. Technically, shock absorbers is a misnomer because their primary job is to reduce the frequency of rebounds, and not absorbing “shocks” from road defects. Worn out shocks allow the bouncing up and down to continue longer than do new ones.