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I
have a KDX 200 and my rear shock spring
is way too soft. My dealer wants almost
100 bucks for a heavier spring. Is there
anything I can do to stiffen the rear end
without popping for the hundred? Thank you.
Joe
Average
I
have a 1987 Ford F-150 set up for fun off-roading,
but the front end is way too soft on the
bumps. I checked on heavier (stronger) springs,
but can't afford them. Is there anything
I can do?
John
Average (Joe's brother)
These
mythical letters are actually representative
of many we've received. The problem is not
isolated to the KDX enduro bike, or the
popular Ford trucks. Nope. Just about any
rider or driver who rides/drives aggressively
will find out that the standard spring(s)
that came on the bike/truck are just not
beefy enough.
To
get our new spring rate, we cut the
coil of the spring off at this point. |
For
maximum safety, hang the spring over
a bucket filled with water before torching
off the unwanted coil(s). |
The
newly cut top coil should now be heated
to a dull red and gently bent down before
grinding it flat. |
That
new top coil should now be ground flat
to sit in the mounting just like the
original spring shape. |
Here
you go: one completed spring that's
stronger than stock, ready to be mounted. |
The
dead (or inactive) coils are those that
touch at both ends when mounted. |
Here's
the basic info needed to determine spring
rate. |
A
number of factors determine the actual
rate of the spring, including the diameter
of the coils. |
You
should also measure the thickness of
the coil wire itself. |
The
information you see here is based on a single-shock
dirt bike, but applies to most any coil
spring, whether it's used on a truck, SUV,
or buggy.
The
owner of a new bike will often not notice
that his spring is too soft at first, because
of the sensation of a fresh, tight new bike
and the attendant careful riding. However,
once he gets the unit broken in and scratched
up a few times he may find himself resorting
to the preload adjustment rings.
And,
no matter what his owner's manual states,
increasing the preload will not keep the
shock from bottoming out under hard riding
conditions. The answer, of course, is a
heavier spring. Naturally, the correct amount
of sag in the rear end and reasonable amounts
of preload will have substantial effects
on the action of the rear end, but it's
possible to have the right amount of sag
for the rear suspension and still have a
too soft spring.
MODIFY
YOUR OWN SPRING
Let's say you've exhausted all the normal
preload and have, in fact, determined that
your spring is too soft. You can avoid spending
anywhere from 75 dollars to well over a
hundred for a shock spring and equivalent
bucks for fork springs. Yes, this low-bucks
approach to customizing your springs works
on the fork springs, as well.
You're
going to need access to a set of torches
and a decent bench grinder to get the job
done right. First, here's how the procedure
is done, then we'll show you how to calculate
just how much you want to cut off your spring
to increase the stiffness.
WAIT
A MINUTE! HOW CAN CUTTING A SPRING MAKE
IT STRONGER?
Gotcha, didn't we. You see, a number of
things determine the rate of a spring, among
them the thickness of the wire, the diameter
of the coils (to their centerline) and the
number of active coils. As a rule of thumb,
the fewer active coils, the higher the spring
rate-all other things being equal.
Since
we can't change the thickness of the wire,
or the diameter, this leaves the number
of active coils as the only variable we
have control over.
Dead
coils are those at each end of the spring
that make contact with something.
If
you have a spring with, say, ten coils,
then two of them are dead (inactive) and
eight of them are live (active) coils. But
enough theory for now. Let's get back to
the actual operation of making our springs
stronger.
STEP-BY-STEP
SPRING MODIFICATION
Once you've determined just how much you
need to cut off your spring to make it stiffer,
here's the procedure. Put some water in
a bucket and lay the spring over the edge.
Not only will this make a solid holder for
the spring, but it will give the hot coils
and sparks a very safe place in which to
drown themselves out.
A
mark should be scribed on the coil where
the cut is to be made. Heat up the coil
with a normal welding tip until it's cherry
red and just starting to turn yellow. When
the metal starts to puddle or melt, turn
off the acetylene. The oxygen will feed
the hot spot and the wire will literally
burn.
At
this point, you are merely feeding oxygen
to an existing point of combustion. The
wire is actually burning! Of course, you
can simply take a cutting torch and blaze
it off, but this technique is much cleaner
and very easy to master. You might experiment
with a scrap piece of metal first to get
the feel.
Next,
place the shortened spring firmly on a flat
surface or in a sturdy vise. Then start
heating the top coil about an inch from
the freshly cut end, very slowly. Do not
overheat it. Once it turns cherry red, you
can squeeze it gently together with a sturdy
set of pliers.
The
key here is gentle pressure. If you force
it too much, there's a chance that you'll
crack the spring and render it useless.
Remember, easy pressure and fairly low heat-just
enough to let the coil start to sag under
a light squeeze.
After
the first part of the coil has been bent
down a bit, back up another inch and heat
some more, then gently put additional pressure
on the coil. After a few minutes of coaxing
and sensible use of the torch, the top (freshly
cut) coil will be flattened out to the approximate
desired shape.
Now
you have to flatten it so it'll fit flush
against the top (or bottom) of the shock.
A
grinder is essential. You probably won't
have access to one as strong as the one
we used here at Works Performance, but the
job can be done with a bench grinder. Plan
on taking about a half hour of work with
the average home bench grinder. You can
also take the shock spring to almost any
machine shop and talk the guy into surfacing
it for you for a few bucks.
One
word of caution: After you heat and bend
the top coil, do not quench it in water
to cool it down too quickly or you might
make the spring take a set. Wait a few minutes
until all the color has disappeared from
the spring. Your spring is now ready to
be sanded clean and repainted. And, if your
calculations were correct, you would now
have the new heavier spring rate you were
after, at no cost to you.
HOW
TO FIGURE OUT HOW MUCH TO CUT OFF
First off, you should know what the rate
of the spring you're using is. That's easy
enough. All springs are coded in some fashion
and the owner's manual tells you what the
different springs are. Some use a grind
mark, while others use paint to identify
the rate.
Let's
say you're starting out with a 600-pound
shock spring. If your shock is too soft,
a ten-percent increase in poundage would
be a logical place to start.
You
have to take the rate of the spring (600
pounds) times the number of active coils
(in this case, 8.875 coils) and divide this
by the desired rate. Sounds like tough math,
but it isn't. Here's how it looks on paper:
600
pounds times 8.875 active coils = 5325.000
Now,
take this number and divide it by the rate
you want, which in our case is a ten-percent
increase, or a rate of 660 pounds. On paper,
again, here's the story:
5325
divided by 660 = 8.0682
This
leaves you with the magic number of 8.0682,
which is the number of active coils that
will give you a 660-pound spring. Pretty
neat, eh? In our spring, that means that
we would have to cut off 7/8 of one full
coil to get what we were after.
Once
again: It's only the active coils that count.
So, out with the torch, zap on the grinder,
and 7/8 of a coil later, you have your 660-pound
spring.
WORDS
OF WARNING
Don't get in over your head. And don't try
to ask a spring to do too much. One of the
things you must watch out for is coil bind.
A spring should never be forced to bottom
out against itself.
If,
for example, you have five inches of available
spring movement and the shock travels 4-1/2
inches, it's clear that you should cut no
more than half an inch off that particular
spring.
It's
not too difficult to calculate just how
much available spring travel you have in
any spring. Merely measure the thickness
of the wire, count the number of coils and
then measure the space between the coils
and count the number of spaces. Basic math.
SPRING
RATES EVEN YOU CAN UNDERSTAND
A typical straight-rate spring is a very
easy animal to understand. Let's say you
have a 100-pound spring. This means that
when the spring is compressed one full inch,
it'll have 100 pounds of force.
If
you did this one inch of compression on
a bathroom scale, the scale would read 100
pounds. When the spring is compressed two
inches, it'll read 200 pounds, at three
inches, 300 pounds-and so forth. Of course,
there are progressive springs, but the math
on them is complex.
PRELOAD,
CONFUSING THE ISSUE
Preload is close to black magic to many.
Let's go back to that 100-pound spring we
were talking about. If you added 1/4-inch
of preload to that spring, the first inch
of travel would yield 125 pounds of force.
One-half inch of preload would bring it
up to 150 pounds, and so on.
However,
preload affects only the first inch of travel.
After the first inch of travel, the spring
will still gain only 100 pounds with each
additional inch of travel, no matter how
much the preload. This is where a lot of
people blow it. Ideally, a light preload
will let the wheel react to small bumps
properly. Way too much preload will make
the finest shock (or forks) feel miserable
on the small bumps, then the suspension
will still wallow through the mid- stroke.
CAN
I DO THE SAME BASIC STUFF TO FORK SPRINGS?
Of course you can. You just have a much
longer spring and may have to count a lot
more when you add up the active coils. Let's
assume you have an 18-pound fork spring
and you feel that it's too soft. Your calculations
show that if you cut off three coils, you'll
end up with a 20-pound fork spring, which
is what you want.
Fine.
Go for it. But make sure that you make up
the space you take away. If you cut off
two inches of fork spring, you must replace
those two inches with some sort of a spacer.
If not, the forks will tend to sag and dive
too much from lack of proper preload.
The
same, naturally, is true of the rear. If
you don't have enough threaded area in your
shock body to make up for the removed coil
area, you will have to fabricate a simple
spacer to take up the room.
MYTH
DESTRUCTION FOR YOUR AMUSEMENT
Some years ago, several companies offered
"booster" springs for forks. These
were said to stiffen up the stock fork springs
and make the forks work better. Hundreds
were sold, most often to owners of Japanese
dirt bikes.
Think
about this for a moment If you had
a set of 20-pound fork springs and
then added a 100-pound "booster" spring
on top of them, in effect you would
be softening the actual spring rate.
Preposterous, you say? Impossible?
Not really
The
formula for figuring out rates with
double springs is as follows: Take
the individual rates multiplied and
divide them by the individual rates
added. Therefore, we have 100 x 20 ÷ 120,
or an actual spring rate of 16.6 pounds.
Obviously,
the initial feel of the forks would be stiffer,
but only because of greatly increased preload.
The mid-stroke rate would actually be less
than with the stock spring. There would
be a slight gain in resistance to bottoming
out with this setup, as the oil level would
be raised a bit.
HELPFUL
HINTS AND COMMON SENSE
You might run into kg readings instead of
pounds when you check your owner s manual.
Do not be intimidated. Should you want to
change them into something real 'Mericans
understand, merely take the number and multiply
it by 56 pounds. For example, you have a
7.9 kg spring: 7.9 x 56pounds = 442.4 pounds.
Ideally,
your spring should be matched to your damper.
And the correct word is damper, not dampener.
If you run a horribly heavy spring that
the shock is not capable of controlling,
then you'll have a rear suspension that'll
bounce around like a basketball every time
it recoils from a bump
When
you do increase your spring rate, you should
also (normally) increase your rebound damping.
Most modern shocks have some sort of adjustment
that will let you change the rebound settings
To
increase the rebound on forks it may be
necessary to go to a heavier fork oil, as
not all forks have adjustable rebound.
Here's
a great formula to have handy if you want
to calculate the rate of a spring when you
don't know the rate:
RATE
11.5 x Wire Diameter to the fourth
power (D4) ÷ by 8 x Number of
Active Coils x Mean Diameter cubed.
You
won't be doing this between rounds of the
TV boxing match Better you should look it
up in your manual.
Special
thanks to Works Performance Products, (818)
701-1010, for tech advice and guidance.
These guys make great bike shocks for any
machine.
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