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Compression, rebound, bump, stroke....what does it all mean?
In graph form, shock absorbers plot force (on the vertical axis) versus speed of shock-piston movement
in the shock body (on the horizontal scale). In this graph, rebound force is in the upper portion,
while bump is in the lower portion of the graph. The dotted line represents a stock shock, while the
solid line represents a firmer rebound and compression force. Adjustable shocks would offer several
lines of greater force based on the adjustment from full soft to full hard.
Better handling on your favorite twisty primary highway calls for a whole different set of shock
requirements. Generally, this can start with a shock absorber that is shorter in length because the
vehicle has been lowered, but also because the amount of suspension travel is greatly reduced. These
shocks are almost the opposite of the drag shocks, since rebound damping is greatly increased given
the increased spring rates that road-race-style cars generally employ. This is another area where
adjustable shocks are an excellent investment. The key is to first choose a front and rear spring rate
that works, and then begin tuning the ultimate handling and the relationship of the front to the rear
with the shocks.
Up to a certain point, a stiffer shock, especially in rebound, is advantageous. But there also comes a
point where a stiff shock will not allow the suspension to react to ruts or tall bumps. This stiff
rebound allows the tire to skip over the tops of a series of bumps such as a washboard asphalt exit
ramp. When this happens, the tires physically lose contact with the road, which means you've just lost
all traction. This is quickly followed by a possible spin. If you've ever driven a car with too-stiff
shocks, you know this is an extremely disconcerting and evil situation. This is yet another reason why
adjustable shocks are a good idea. Another situation that can affect this is when you change to
significantly lighter-weight wheels and tires on an otherwise optimized shock package. Suddenly, the
car is very skittish because of the reduced unsprung weight.
