Making your car handle better isn't easy. Camber, caster,
toe, roll centers, motion ratios-suddenly building a show car sounds like a
pretty good idea. Aside from tires, your coilover shocks are the single most
critical component to your car not handling like a turd. But if selecting the
right coilovers were easy, show cars would be in short supply. Besides the more
conventional type of coilover shocks that are standard equipment on most cars,
there are also high performance versions, slip-fit coilovers and full-bodied
coilovers. The choices don't end there, either: preload, material options,
damping adjustability and the whole mono tube versus twin tube enigma is enough
to make anyone care more about stuffed animals dangling from purple tow hooks
than going fast.
Making your car
handle better isn't easy. Camber, caster, toe, roll centers, motion
ratios-suddenly building a show car sounds like a pretty good idea.
More than one coilover exists!
Not all coilovers are created equal. In fact, there are
three kinds: OEM style spring over shock assemblies, slip-fit coilovers and
full bodied coilovers. OEM-style spring-over-shock assemblies are based off of
a conventional shock, or strut assembly, that's surrounded by its own coil
spring. Such all-in-one coilovers are typically non-adjustable, feature
fixed-length bodies and are precisely what you have no interest in reading
about. Slip-fit coilovers are marginally more exciting and only slightly more
complex. These consist of a hollow, threaded (usually aluminum) tube that slips
over and sits on an existing shock's perch and, with the help of a series of
jam nuts, compresses or decompresses its spring to alter ride height. There's
virtually no performance gain to slip-fit coilovers, but they can be a quick
and inexpensive way of dumping your car.
Full-bodied coilovers are what you've been thinking of since
paragraph one. Full-bodied coilovers replace the entire factory spring and
shock assembly and feature a threaded shock body for easy ride-height
adjustments and, often times, adjustable damping. Similar to slip fit
coilovers, ride height adjustments are made through a series of jam nuts and by
compressing or decompressing their springs. Higher-end coilovers also feature
threaded lower bodies and lower mounts that can be screwed in and out for
further ride height adjustments, essentially shortening the shock without
altering spring compression. Another characteristic of higher-end, full-bodied coilovers
is a shortened shock body, which allow for an even lower ride height without
the risk of bottoming out.
Full-bodied
coilovers are what you've been thinking of since paragraph one.
Aside from the shock body, spring, jam nuts, and lower
mount, the full-bodied coilover assembly may also include bump stops, dust
boots and an upper mount assembly. Upper mount configurations vary depending on
whether or not the suspension is based upon a double wishbone or MacPherson
strut layout. Double wishbone layouts typically feature fixed upper mounts with
rubber or polyurethane bushings while upper mounts designed for MacPherson
setups typically include pillow-ball assemblies with camber and caster
adjustability.
The shock body
At the heart of the full-bodied coilover is the shock. Like
any shock, the coilover's upper mount connects directly to the chassis while
its lower mount connects to its lower A-arm in double wishbone layouts or the
knuckle itself in MacPherson strut configurations.
Shocks control unwanted spring oscillations and reduce
vibrations caused by the wheels and chassis. When you hit a bump, the
suspension's springs compress and decompress, absorb vibrations and transfer
energy to the shocks through their upper mounts, into their pistons. As a result,
the shocks dampen the vibrations, making that bump virtually unnoticeable. The
degree to which all of this happens depends on the shock's internals: stiffer
shocks slow spring movement while softer shocks do the opposite.
Shocks do more than just reduce vibrations and control
spring movement, though; they also eliminate rocking, pitching, dipping, wheel
spinning and all sorts of other things that aren't supposed to happen when
turning or stepping on the gas or brake.
Inside the shock lies a hydraulic fluid-filled tube and
piston. The piston pushes high- pressure fluid through the shock's valves,
controlling how it responds against the spring. Kinetic energy harnessed
through suspension movement turns into heat energy that ultimately dissipates
within the shock's fluid. Valving is based upon small orifices perforated into
the shock's piston that allow hydraulic fluid to bleed through as the piston
travels up and down.
Mono tube vs twin tube
Modern coilover shocks are offered in two configurations:
mono-tube and twin-tube. Mono-tube shocks feature a piston and rod assembly
housed within the damping case where both compression and rebound duties occur.
Twin-tube shocks feature two cylinders the inner cylinder where the piston and
shaft move up and down, and the outer cylinder, which serves as the hydraulic
fluid reservoir.
Twin-tube shocks allow for increased piston stroke, which
can benefit ride quality and handling, but seldom overshadow the mono-tube
design. Compared to twin-tube shocks, larger-diameter mono-tube shocks have the
ability to displace more fluid, resulting in increased sensitivity to small
suspension movements at low shaft speeds. The increased flow also allows for
more consistent damping forces when compared to less expensive, twin-tube shocks.
Most mono-tube shocks also run cooler than twin-tube designs because of their
missing outer tubes.
It seems the mono
tube design is better because of its higher piston rigidity, longevity,
serviceability and improved lateral load performance and heat dissipation.
Shock travel
When selecting coilovers, making sure you've got enough
shock travel is key and will help prevent bottoming out. In case you didn't
know: bottoming out is bad and defeats just about every single suspension
modification. You've made. The more travel, the better a shock can do its job.
Spring choice also determines how much travel you'll need. Stiffer springs
require less travel since the shock won't be able to compress as much.
