posted Apr 21, 2011, 2:53 PM by LRP Admin
[
updated Apr 21, 2011, 2:59 PM
]
Article Originally Published Joe's Racing Products Web Site
http://www.joesracing.com/kb/question.php?ID=4 |
Shocks are an important tuning tool that create feel
in your car. With the variety of shock brands, components and types
partnering up with a shock specialist can help you to navigate through
the vast array of component offerings.
To increase our shock knowledge, we have interviewed two successful
specialists in the shock field. Mike Naake of Naake Suspension
Specialists and Mike Leary of Leary’s Shock Shop offer their suggestions
and experience. Both “Mike’s” provide shock hardware, setups and
technology to prominent racers across the country and are authorized
service centers for many of the major shock brands.
With so many shock choices on the market how can you help racers choose the correct type?
Leary:
It is important to buy the most tunable shock within your track or
organization’s rules. If your rules allow for compression and rebound
adjustment the additional initial investment will translate into speed.
If your rules dictate twin tube designs then the more economical
hardware can be maximized through tuning. When rules allow we want our
teams to utilize the options that are made available in pressurized mono
tube shocks.
Naake:
Rules and budget are part of the equation. We tailor our shock
packages to meet the needs of each racer. After a complete interview of
each team we determine if pressurized mono tube shocks will work best or
if the economics of twin tube shocks meet their needs. Once the shock
type is selected we continue the interview to learn more about the goals
of each team and build packages based on their input. Understanding
driver tendencies and track characteristics allow us to tune shocks for
more speed.
What is the racer benefit for partnering up with a shock specialist?
Naake:
Drivers and Crew Chiefs can communicate what they want the car to do
and we can create an option based on the feedback. We can customize and
offer a linear/digressive piston, digressive linear piston, double
digressive piston, and another piston designed specifically for rough
race tracks. Our knowledge is based on feedback from many teams and the
information base gained over the entire group would be impossible to
gain within a single team.
Leary:
With shock manufactures offering ever expanding part options for their
shocks i.e.: pistons, shim stacks, shafts with different bleed options,
etc, it is almost impossible for the racer to stay on top of his shock
program. As shock specialists we are continuously being educated on
latest product offerings from the shock companies we support. Racers
also benefit from our experience – we are testing all the time and the
knowledge gained by working with several teams helps us to understand
the changes needed for each individual team. Our shock dyno runs full
time creating unique shock packages even for teams competing at the same
track.
What is a Mono tube shock?
Naake:
There are two types of late model/sprint car mono-tube shocks,
emulsion and De Carbon style. An emulsion shock is typically a mono tube
shock with gas and oil in the same chamber. The oil and gas mix
creating foam. This is not a desirable situation in any hydrologic
system, especially a racing shock absorber. Christian Bourcier de Carbon
invented the mono-tube pressurized gas shock absorber. A De Carbon
style shock absorber has a dividing piston that separates the nitrogen
and oil. De Carbon mono tube shocks with gas pressure and a dividing
piston perform better than twin tube shocks. Mono tube shocks cost more
to manufacture yet the added expense results in better and more
consistent performance.
Naake uses this photo to illustrate the base valve action on the
mono tube compression stroke. As the shaft displaces the shock oil the
base valve smoothly opens to allow for the shaft volume. Shim stacks can
be seen flexing to meter the precise amount of shock oil.
 The
Naake mono tube rebound stroke photo illustrates shock oil flow and you
can see the internal forces and valving action. The mono tube gas
separating piston is clearly shown at the top of the shock.
What is a Twin tube shock?
Naake:
Many
tracks and weekly racing series’ rules require a twin tube shock. They
do this to keep the racers’ costs down. A twin tube shock has an inner
tube that the piston runs in. At the bottom of the inner tube is a base
valve. The function of the base-valve is to make 30%-40% of the
compression force and replenish the oil in the inner tube on the rebound
stroke. If a base valve is not performing with enough force in a twin
tube shock that could result in cavitation or what we call in a twin
tube design “dumping”. Dumping is when too much oil moves out of the
inner tube too quickly and on the rebound stroke it is not replenished
fast enough resulting in a momentary dead spot on the rebound stroke.
The dumping can be verified on the rebound opening stroke of a constant
velocity test on your shock dyno.
 Naake
uses this photo to show the low pressure gas filled bags utilized in
twin tube shocks. The low pressure bags prevent foaming and deform to
account for shaft displacement. The Base Valve adds 30 to 40% of the
compression force.
 Naake
points out twin tube shocks have an inner tube that the piston runs in.
The twin tube rebound view shows the base valve metering oil from the
outer oil reservoir.
Why run a base valve?
Leary:
Base
valves are of most benefit on heavy cars and when low gas pressure is
used. For most late models we run without base valves in mono tube
shocks to save cost. As you run high compression it can make sense to
add a base valve to help prevent cavitation on the back side of the
piston. When running a base valve the shock valving needs to be tuned to
line up with the compression forces that are metered through the base
valve.
Naake:
A
base valve is an optional component on a mono tube shock and works
great with low pressure. Some series that allow mono tube shocks do not
allow base valve to be installed. A base valve shock will have a much
smoother feel to the driver than a non-base valve shock. Of course, a
base valve in a shock adds to the cost. We are big fans of base valves
when rules allow. The added control of the oil displaced by the shaft
gives us more choices with our rebound adjustments as cavitation is
eliminated through transition from compression to rebound.
Is shock oil important?
Leary & Naake:
Shock
oil is a part of the shock that most racers overlook. Many manufactures
use inexpensive hydraulic oil in their shocks. Inexpensive oil can vary
through out the temperature range. You may start the race with a shock
that has a 5 valving on compression and rebound. Inexpensive oil may
react dramatically with heat and effectively make the 5 shock you built
in the shop perform like a 3 shock on the track. Using thin synthetic
oil reduces the viscosity change allowing for more consistent shock
performance from ambient temperature to race temp.
Using
a drip cup for shock rebuilding keeps the oil contained and your
workplace clean. An organized shock building station is a must if you
are servicing shocks on your own.
Leary
tested several 5 shocks from different companies. This graph shows that
a 5 shock valving varies significantly from brand to brand.
Understanding the brand valving differences will help you to make the
proper adjustments when using competing brands.
What Shock tips can you give to our readers?
Naake:
We
hear a common myth that bag shocks blow out due to rough track
conditions or sudden high velocity compression. In my experience, I just
do not see this at all. The only bag failures I have seen are due to
errors in assembly or a bag had a small puncture prior to assembly.
You
can perform a simple hand test of your twin tube style shock. Fully
extend the shock. Position the shock so that the shaft end is up.
Compress the shock about a half an inch. If you feel any slack or a dead
spot, it is an indication of air in the system. This can be caused by
the shock being low on oil, either from the shock having an oil leak or
from not enough oil placed in the shock during assembly. It could also
indicate a leaking gas bag. We perform this test on all twin tube shock
prior to running a dyno test. If they don’t pass the hand test, they are
guaranteed to fail the dyno test.
Leary:
You
should have your shocks dyno’d when they are new to get a baseline, and
then should be re-dyno’d after a crash and halfway thru the season. A
shaft bent 3 or 4 thousandths or a tiny dent in a mono tube shock body,
will change the shock dramatically. In this day in age, it is almost
impossible to build your own shocks without testing them on a quality
dyno. Using the proper tools such as, shock wrench, shock vice and drip
cup will make the building process easier and protect your investment.
Keeping your shock work area clean and organized is pivotal to building
successful shocks.
If
you are going to work on your own shocks then using the proper tools
such as a shock vice will help you to build winning shocks.
What shock adjustment tips can you suggest?
Leary:
Most
of the handling of a pavement car is controlled in the first 2 inches
of shock movement. I like to use the rear shocks to control the entry of
the corner, left side shocks and RF for the middle of the corner and
the fronts for exit.
I
avoid using the compression side of the shock for handling adjustment. I
would rather use springs to control compression adjustments. The one
exception is possibly the compression on the left rear – by increasing
the compression at certain speeds, you can gain bite off the corner. It
can make the car think is has more LR spring on exit without changing
the corner entry like a spring can.
On
a conventional spring setup, the shock settings will work differently
than with a soft spring set-up. The more front spring rate, the less
compression you need because the spring is doing the work. With a soft
front spring set up, you need to use compression to control the speed of
the front end movement because you have a 200 lb spring trying to hold
up an 800 lb corner.
If
you tie down the left rear shock on a conventional set-up, I’ve found
you will tighten up the entry of the corner. I believe it keeps the left
rear weight from transferring to the RR as fast, which gives you that
loose entry feeling and keeps the weight on the LR tire.
With
a soft spring set-up, if you tied down the LR, it usually will loosen
the corner entry. Because of the rapid weight transfer to the RF of the
car, we can overload the RF tire, which can cause a soft push on entry.
By delaying that transfer the RF tire has a chance to “grip” the track,
so the driver feels the car is looser on entry.
With
either conventional or the soft spring set up, the rebound on the RF
can help that “tight in the middle” feeling. By stiffening the rebound
on the RF it holds weight on that tire and helps it maintain grip – it
also keeps the RF from transferring weight to the LR as fast, which will
cause the car to pick up a push. The downside of holding down the RF is
you can lose some grip off the corner, because you are delaying that
weight transfer to the LR.
When
we have soft front springs, we need the rebound on the LF shock to help
the sway bar to keep all that weight transfer to the RF. That is why we
see the extreme tie-down LF shocks. It is important to balance your
front springs/sway bar and tie-down in the LR shock. We build LF shocks
at 1 inch of travel anywhere from 600 lbs of force to 1000 lbs,
depending on the set up.
 Changing
the sweeps on externally adjustable shocks makes a big change. Leary
uses this dyno graph to illustrate the dramatic effect of using sweep
adjustments.
Naake:
To help free up the car from the center off a quick
adjustment is to add gas pressure to the RR shock. By adding up to
200lbs (if you have the right hardware) the car can take on a better
attitude and become more stable on exit. This fix is quick and can be
removed quickly if the driver is still looking for a better exit.
With today’s set ups we like to maintain rebound in the front shocks.
If the car is tight, and if the team has the right hardware, we try to
go with high frequency pistons to relieve the tight feeling. In short,
there is an o-ring behind the shaft band that delays the metering of oil
through the bleed holes for a brief moment and then shuts the bleeds
off just as quickly. Our teams can work with us to discuss these options
to find more speed – our goal here is to let your readers know that
there is high tech hardware out there that goes beyond generic answers.
We have proven results in gaining front grip off the corner with the
high frequency hardware available. Remote canisters provide another
layer of adjustability when allowed.
While high tech is cool sometimes a basic answer works well. If your
car is tight then more compression in the RR will help the car turn in
the center. You can try a bit more rebound in the LR to free it up. You
can take a little compression out of the LF or tie down the RF to help
the car turn. Extreme rebound in the front shocks is good in many cases
but too much low speed control can reduce front grip. With extreme front
rebound you need some bleed to allow the tire to follow the track
surface.
 When
rules allow a remote shock canister gives you more compression
adjustability options. Base valves can be built into remote reservoirs
and the housing needs to be protected from damage. Using a canister
mount allows for quick adjustments when practice time runs short.
Summary:
Butcher:
Shock science and hardware is constantly changing and the application
of the set up tips is very dependant on the track, driver and location
in the turn. Many times a standard shock tip will change 180 degrees
based on moving the car a few feet in the corner and the tips above need
to be applied with full understanding of shock mechanics – both Mike’s
will change their adjustments based on real world data. When it comes to
shocks it is all about timing and transitions. Shocks might hold or
delay movements but in the end the springs carry the load. Bumps,
braking, throttle and rolling through the middle all provide information
that will be analyzed independently by your shock guru. Be aware that
you may have soft front springs but you also must consider the overall
front spring rate based on the giant sway bar that could be in your car.
Go Forward – Move Ahead
Jeff Butcher
Courtesy of JOES Racing Products
www.joesracing.com |
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