Suzuki RG500 GAMMA

From Moskito1@aol.com Fri Mar 27 16:11 MET 1998
From: Moskito1 
Subject: Fwd: Shock Tech Article - LONG, I'm tired of typing...
Subject: Shock Tech Article - LONG, I'm tired of typing...

Here's a tech article concerning spring rates and some aspects of suspension
tuning.  It's from a company called:

Custom Axis
2499 South Stockton Street, Suite 1
Lodi, CA 95240
(209) 368-5046
(209) 368-5119 Fax

Mike Hallock (not sure about last name) was a Fox Factory tech, worked for
Penske, I think worked for WP for a time also, and then started his own
business - Custom Axis.  Penske just bought his business, keeping him as "Main
Man" in the shock dept.  The guy knows his stuff!  He does custom jobs, using
all custom in house machined parts.  No welding in any of his products.  Lots
of attention to detail, such as hard anodizing of all aluminum (7075-T6) parts
and either 17-4 stainless or 4130 chromoly for shock shafts.  All other steel
parts are 303 or 17-3 stainless.  I have full intentions of looking into a
Custom Axis shock for the RG - replacing the Fox - and intend on doing the
same on my Pilot...ever see a 36" long shock w/13" of travel?

Here's the article.  Please remember, most of his shocks go on ATVs so some of
the stuff doesn't quite cross over to motorcylces, but it's good info anyhow.

1.0 Suspension Design
Having the right spring(s) and motion ratio is a very critical part of any
suspension system.  The spring(s) resist the forces of input from the ground
to the chassis, the suspension's motion ratio determines how the spring(s)
will operate, and the shock absorber controls the spring's reaction to those
inputs.  Obtaining a desired leverage curve, and spring combination is the
starting point of building a suspension system in relationship to how a
suspension system works, you need to know a little bit about motion ration,
spring rates and shock absorber dampening.

1.1 Motion Ratios
The motion ration or ‘leverage ratio' is the path the shock absorber goes
through its travel in relation ship to wheel travel.  This is determined by
the type of suspension hardware arrangement and geometry that the chassis
manufacturer decides to use.  The most commonly used suspension hardware is
either a linkage type or a direct shock type, more commonly referred to as a
‘no-link'.  The main difference between linkage and no-link type systems is
packaging.  Linkage systems in general utilize less space to operate, while
no-links by nature of design usually require more space.  Both types, however,
have their assets and drawbacks.  It is not the purpose of this manual to
argue which is better.  There are too many variables to consider.  However, it
is important to note that all linkage systems are not the same, all direct
shock systems are not the same, and all shock absorbers are not the same.

1.2 Springs
Most of the springs you will see are straight rate or linear compression
springs.  Linear means that there is a constant progression of force in
relationship to compression movement.  For example: a linear spring with a
rate of 200lbs. means it takes 200lbs. of force to compress that spring one
inch. (One inch + 200lbs., 2 inches = 400lbs., etc.)

With a dual rate spring combination, you have two springs stacked on top of
each other and they are compressed simultaneously.  Because both are moving at
the same time, it takes less force or poundage to compress both springs one
inch.  Fore example: When you compress two linear 200lb. springs stacked on
top of each other for one inch, both springs are going to yield a linear rate
of 100lbs..  Both of the 200lb. springs will have compressed ˝" 05 .050".  By
multiplying the spring movement .50" by the spring rate 200lbs., it will give
you the working spring rate (200 x .5 = 100).

The main purpose for using a dual rate spring combination is to enhance the
progression of the chassis' motion ratio.  A dual rate spring stack consists
of two springs, a short tender spring on top and a long main spring on bottom.
This progressive rate system is used to produce a lighter initial spring rate
for a desirable lower ride height as well as providing a smooth, supple ride
over small surface irregularities.  Then, at a determined point in the shaft
travel, via the tender cross over height, the tender spring stops working and
the initial rage then crosses over to the stiffer rate of the main spring.
This progression to the stiffer rate is used to prevent harsh bottoming during
high speed input, such as jumps or whoops, and also to prevent excessive
chassis roll in corners.

The important thing to remember is that springs are resistance poundage.  It
takes a given amount of preload poundage to establish a desired ride height, a
given amount of spring poundage to prevent chassis roll and a given amount of
final poundage to prevent extreme bottoming.  Having the right spring
combination and the correct cross over height is crucial to suspension
performance.

1.3 Dampening
The function of the shock absorber dampening is to control the springs's
reaction to input. This is done using a special piston called a dampening
piston.  It is attached to the end of the shock shaft inside the shock body.
The dampening piston has special through passages or ‘ports' that allow fluid
to pass from one side of the piston to the other.  On either side of the
piston there is a series of tuning washers or ‘valve shims' which seals off
fluid flow in one direction and restricts or ‘dampens' fluid flow in the other
direction.  When the shocks compressed or retracted, the dampening piston
moves through the shock fluid, forcing the fluid through these passages.
Dampening is thus regulated by the assembly of the valve shims on either side
of the dampening piston.  Compression dampening regulates how fast the spring
will compress, and rebound dampening regulates how fast the spring returns
after being compressed.

The compression dampening should be taut, firm, but not harsh.  Too much
compression dampening and the ride will be stiff and choppy.  Too much
compression dampening could also cause the shock to become solid or
‘hydraulic'.  This causes a number of undesirable effects, tow of which is
blown seals and bent shafts.  Too little compression dampening and the ride
will be spongy and vague.  Not having enough compression dampening will also
cause you to blow through the travel too fast.

The rebound dampening should be on the slow side, but not too slow or the
shock will ‘pack up'.  Pack up means that after the shock has been compressed,
the speed at which it returns is too slow to reach proper extension before the
next compression stroke.  With a gradual loss of shaft travel at each
compression stroke, the shock could eventually run out of shock travel and
bottom out.  Not enough rebound dampening, the ride becomes springy with a
buoyant feeling. In either case, not having the correct rebound dampening
prevents the tires from not staying planted on the ground, causing them to
skip, wander and bounce, which results in loss of traction and control.

2.0 External Shock Adjustments
A fully adjustable racing shock has four means of external adjustment:
Preload, Tender Spring Crossover Height, Compression and Rebound Dampening.

2.1 Static Preload
Static preload is the amount of spring poundage your shock has in an unladen,
fully extend condition.  Basically, it's how much the spring or springs are
compressed when installed on the shock.  Example, you put a 300lb. spring on
your rear shock and the spring has a free length of 10.00 inches before
installation.  After installation, you measure the spring again with the shock
fully extended, and the compressed length is now 9 3/4 inches, or .25" of
preload.  Then multiply the spring preload by the spring rate and that will
give you static preload (300lbs. x .25 = 75 lbs. of static preload).

The main purpose of preload is to raise or lower the vehicle's ride height by
means of adding or subtracting spring preload poundage.  NEVER add preload to
prevent excessive chassis roll and bottoming.  By raising or lowering the ride
height, you are also moving the vehicle's center of gravity, or ‘CG', up and
down as well as changing the vehicle's weight bias, either the front of tho
the back.  Optimum ride height is a balance between a center of gravity low
enough to maintain good cornering stability and a chassis clearance high
enough to prevent the frame from hitting the ground.  It's ok to graze or
scrape the bottom of your frame now and then, but you don't want it slamming
the ground, knocking your hands and feet off.

2.2 Tender Spring Crossover Height
Tender spring crossover height is directly related to chassis roll and bottom
out forces.  Changing the tender spring crossover height is the most
significant handling change you can make, using the shocks' external
adjustments.  The crossover height movers the dural spring's point of
progression in relationship to the shaft travel and motion ratio.  Increasing
the crossover height decreases tender spring travel, making the main spring
crossover sooner in the wheel travel, providing stiffer spring poundage for
more spring resistance during chassis roll and bottoming.  Decreasing the
crossover height increases tender spring travel., making the main spring
crossover later in the wheel travel, resulting in less spring poundage for
softer spring resistance during chassis roll and bottoming.

Therefore, increasing the tender spring crossover height makes the suspension
stiffer.  Decreasing the tender crossover height makes the suspension softer.
Your suspension should bottom out at least once somewhere on the track not so
hard to where you feel the footpegs through your boots but enough to know that
your using all the available travel.

SPRING FORMULAS

Spring rates are determined by how many pounds of force it takes to compress a
spring one full inch.
To rate an unknown spring:
11,500,00 x wire diameter to the 4th power
---------------------------------------------------
8x(spring ID + wire diameter) cubed x active coils

example:
wire diam .362; Spring ID 2.575; active coils 9.2

   11,500,00 x (.362)^4
-----------------------------
8 x (2.575+.362)^3 x 9.2

Your rate is 105.9

To figure active coils:
hold spring upright and start from the bottom.
When the flat end coil comes in contact with the first coil, that's zero.  Up
from there count the number of turns until it touches the other flat end coil.
In most cases it won't end up on an even number.  Divide the full turn of the
spring into 10 units, take this and use it for the fractional determination of
the spring coil where the flat coil touches again.  You will end up with an
active coil number such as 9.6 or 7.8 or 8.5 .... 

To convert to metric Kg:
Divide pounds by 55.88
Divide inches by .03937

To figure out the combined rate using multiple springs:
The formula for two springs is 1/K+1/K2 =1/K3
For three springs it's 1/K+1/K2+1/K3=1/K4
(K=spring rate)

Example: You have an #80 Tender and a #370 spring combination.
1/80+1/370=1/K3    K3=#65.8

If you need to cut a spring to obtain a desired rate use this formula:
K1+AC=K2+AC    (K=Spring rate, AC=Active Coils)
Example: a #60 spring with 8.5 active coils = #78.5 x 6.5 active coils

Richard

Oh one other thing...I ran a spell checker on it...so if you find anything
wrong, complain to Word Perfect 6.1.....

Rob Koopman ( Rob.Koopman@inter.NL.net ) ^{RG500 Index}