Q: What is the science behind the variable rate ktm shock springs?

A: MANY PEOPLE WILL EXCHANGE THE PDS VARIABLE IN FAVOR OF A STRAIGHT RATE SPRING AND ARE ABLE TO MAKE IT WORK AND BE HAPPY WITH THE PERFORMANCE. THE VARIABLE STOCK PDS SPRINGS ARE TOO VARIABLE. THE FACTORY QUOTES RATE CHANGES OF 1.8 TO 2.2 kg/mm. BUT IN ACTUALTY ARE 2.5 TO 3.0 kg/mm. WE HAVE DEVELOPED A VARIABLE RATE SPRING THAT INCREASES BY 1.5 TO 2.0 kg/mm. EVERYONE THAT HAS USED THEM LOVES THEM. TWO OF OUR CUSTOMERS WERE ABLE TO ADVANCE UP ONE CLASS.

THE WAY THE FACTORY RATES THE SPRING IS; RATE AT 10mm AND THEN RATE AT 100mm. THIS IMPLIES THAT YOU HAVE TWO RATES, WHILE IN REALITY THE SPRING CHANGES RATE CONSTANTLY, ALWAYS GETTING STIFFER.

SOME SPRINGS WILL REACH A RATE PLATEAU AFTERWHICH THE SPRING WILL NOT CHANGE RATE, WHILE OTHERS WILL ALWAYS BE VARIABLE. MOST SPRINGS WILL STAY VARIABLE FROM START TO FINISH WITHIN THE USEFUL TRAVEL AND ADJUSTMENT OF THE SHOCK.

Q. How do I get the shock apart to install a new shock spring?

 A. THE PROCESS I HAVE USED FOR THE XR50 SHOCK SPRING:

  • PRESS OUT THE STEEL BUSHING IN THE ALUMINUM END
  • THEN PRESS OUT THE RUBBER BUSHING
  • PULL RUBBER DOWN OVER SHAFT EXPOSING NUT
  • BACK UP THE JAM NUT AGAINST THE SHAFT (END OF THREADS)
  • HOLD THE NUT WITH A VICE
  • APPLY LIGHT HEAT TO THE CENTER OF UPPER MOUNT (325o) (700o WILL MELT ALUMINUM)
  • THIS ALLOWS FOR THE RELEASE OF THE LOCK-TITE
  • USE A CRESENT WRENCH, WITH A MODERATE TWIST – TURN IT
  • WHICH ALLOWS FOR DISASSEMBLY

Q. What rate do I need?

A. If you are uncertain about the particular rate, call us at 405-524-7223  and tell us:

Bike Type
Rider’s weight
Style of riding

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PW 50 – REAR SHOCK SPRING REMOVAL AND INSTALLATION

  1. REMOVE THE TWO PHILLIPS HEAD SCREWS RETAINING SEAT. REMOVE SEAT.
  2. REMOVE UPPER SHOCK MOUNTING BOLT – 10MM THEN REMOVE LOWER SHOCK MOUNTING BOLT – 12MM.
  3. REMOVE SHOCK ASSEMBLY.
  4. INSTALL SHOCK ASSEMBLY (LOWER-BOTTOM) IN VISE.
  5. COMPRESS SPRING TO GAIN ACCESS TO UPPER 16MM LOCKING NUT.
  6. INSTALL SUITABLE TOOL – (LARGE PHILLIPS SCREW DRIVER) INTO UPPER SHOCK MOUNTING HOLE AND LOOSEN MOUNT AND REMOVE.
  7. REMOVE SPRING AND PLASTIC COLLAR.
  8. TO INSTALL, REVERSE PROCEDURE.
  9. ANY QUESTION PLEASE FEEL FREE TO CALL US- Cannon RaceCraft Inc. AT 405-524-7223 OR 405-524-0690.

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PW50 – CLUTCH SPRING REMOVAL AND INSTALLATION (PDF printer-friendly instructions)

THESE PROCEDURES SHOULD ONLY BE ATTEMPTED BY A QUALIFIED TECHNICIAN OR YOUR LOCAL YAMAHA SERVICE PERSON

  1. DRAIN ENGINE OIL, OUT OF 12mm BOLT, ON RIGHT SIDE OF ENGINE CASE, INTO SUITABLE CONTAINER
  2. REMOVE REAR RESONATOR, BAFFLE OFF REAR OF EXHAUST PIPE
  3. REMOVE SEAT
  4. REMOVE EXHAUST FROM CYLINDER HEAD
  5. REMOVE REAR BRAKE CABLE ADJ. NUT, PULL CABLE OUT OF SPRING AND PIVOT.
  6. REMOVE REAR AXLE NUT, RIGHT SIDE
  7. REMOVE REAR LOWER SHOCK MOUNTING BOLT
  8. REMOVE RIGHT SIDE UPPER AND LOWER SWING ARM NUTS AND REMOVE SWING ARM
  9. REMOVE PHILLIPS SCREW IN TOP OF CARB AND REMOVE THROTTLE AND CHOKE CABLE – SLIDE ASSEMBLY FROM CARB.
  10. TURN FUEL PITCOCK OFF AND DISCONNECT FUEL LINE FROM CARB, DRAIN INTO SUITABLE CONTAINER. REMOVE FUEL TANK STRAP AND FRONT BOLT – REMOVE FUEL TANK
  11. DISCONNECT SPARK PLUG WIRE FROM SPARK PLUG
  12. DISCONNECT WIRING HARNESS CONNECTORS AT ENGINE (ALL)
  13. REMOVE UPPER MOTOR MOUNT TO FRAME BOLT
  14. REMOVE OIL INJECTOR COVER AND SCREW, REMOVE INJECTOR CABLE, REMOVING OIL LINE AND DRAIN INTO SUITABLE CONTAINER. (PLUG HOSE)
  15. REMOVE REAR WHEEL – CAREFULLY, ENGINE WILL BE LOOSE IN FRAME
  16. REMOVE ENGINE ASSEMBLY FROM FRAME AND SET ASIDE. (USE KICKSTAND TO SET ENGINE ON WORK AREA)
  17. REMOVE PHILLIPS SCREWS AND 12mm BOLT FROM RIGHT SIDE ENGINE COVER. (CAREFULLY REMOVE COVER NOT TO DAMAGE GASKET) MARK PHILLIPS SCREWS UPON DIS-ASSEMBLY. (SOME ARE LONGER THAN OTHERS)
  18. REMOVE SNAP RING FROM CLUTCH SHAFT AND REMOVE CLUTCH HUB
  19. REMOVE CLUTCH ASSEMBLY AND REPLACE WITH NEW SPRINGS, BE SURE TO INSPECT CLUTCH HUB AND SHOES FOR WEAR OR HEAT DAMAGE. INSTALL NEW GASKET IF DAMAGED IN DIS-ASSEMBLY
  20. **INSTALLATION IS REVERSE OF THESE PROCEDURES**
  21. REFILL ENGINE OIL AND OIL INJECTOR RESERVOIR BEFORE START UP.

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UNDERSTANDING COIL SPRINGS

DO SPRINGS GET SOFTER WITH AGE?

Springs do not normally lose rate and get softer unless a coil is fatiguing or beginning to break. A spring can take a set though and become shorter requiring a preload adjustment on the spring collars. High quality springs use the finest quality chrome silicone wire, plus they are heat-treated, stress relieved, shot peened and the ends are carefully ground flat to insure the spring does not take a set.

What if a spring “sets”?

When a spring takes a set it will normally stabilize at its new height. The rate effectively remains the same since no appreciable changes have been made to any of the three factors (wire diameter, spring diameter, and active coils) that determine the spring’s rate. Other than creating a need to readjust the set-up and ride heights of the chassis, the spring should provide satisfactory performance. It is not uncommon for even well designed and properly manufactured springs to settle up to 1% of their free height. However, in some cases where a poorly designed spring is subject to extreme over-stressing, the spring’s height may not stabilize. slots download The spring may continue to change height (shortening and lengthening) as the spring is worked.

CAN TOO SOFT OR TOO STIFF A SUSPENSION BE ADJUSTED WITH SPRING PRELOAD OR A DAMPING ADJUSTMENT RATHER THAN A SPRING CHANGE?

There is a relatively narrow range that each spring rate covers for a rider. If the spring rate is too soft for the rider and he compensates with too much preload, the quality of the ride will deteriorate over small bumps, the steering and stability of the machine will be affected and the suspension may still be too soft. Adding excessive compression damping to increase stiffness will result in a harsh ride. The same is true if the suspension is too stiff. Too little spring preload will deteriorate handling and slow down the machines steering.

WHAT IS COIL BIND?

Coil bind takes place whenever a spring is compressed and one or more of the spring’s active coils contact another coil. The rate of the spring increases whenever a coil binds since the bound coil or coils are no longer active (this changes one of the three rate-determining factors). Handling is affected whenever a spring coil binds. If the spring is compressed to solid height (all coils touching) during suspension movement, the suspension will cease to work. You should check for evidence of coil bind by examining the finish between the active coils. If any coils have bound the finish between them will show contact marks that appear as though they were drawn with a lead pencil. Normally any spring that is binding should be replaced with a spring with proper travel. Springs made from wire that is heavier than what is needed will coil bind before others that are made with the proper size wire.

Under extreme conditions, coil binding can cause a spring to unwind slightly. This can cause the mean diameter of the spring to increase and reduce the rate of the spring. You should realize that the potential for coil bind is increased whenever short springs are used. Always match the spring to the job.

WHY DO SPRINGS BOW?

Springs that have lengths greater than 4 times their diameter will have a natural tendency to bow when loaded. Therefore, tall springs tend to bow more than short springs, and small diameter springs tend to bow more than large diameter springs. Generally, the more a spring is compressed the more it will tend to bow

Use the correct hardware for installation to keep the mounting surfaces as parallel as possible during the suspension travel. Use springs that the ends are ground and squared. If a coil-over spring is rubbing on the shock, try reversing the spring so the bowed part of the spring is around the shaft where there is more clearance.

IS THE QUALITY OF THE SPRING IMPORTANT?

A similar rate spring can be wound using thick wire or thin wire. If both springs were wound with the same number of coils, the spring with the thicker wire would provide a higher rate. But if the spring with the thicker wire has more coils than the thin wire spring, they could be similar in rate. The highest quality racing springs use the smallest possible wire diameter and wider spaced coils. This makes the spring much lighter in overall weight, though the spring rate can be the same as a spring with thicker wire. The problem is that the spring with thinner wire is much more prone to set after use. (See next question about spring stress) To keep this from happening, a more expensive, higher quality wire is required. Quality springs use the best possible wire to reduce the overall weight of the spring.

WHAT IS SPRING STRESS?

The rate of a spring is determined by diameter, active coil count and wire size. Most springs are built to a fixed diameter; a spring designer must decide on the best wire size and coil count to produce the desired rate. If smaller diameter wire is chosen (which can soften the rate), than less active coils (which can stiffen the rate) will be needed to achieve the desired rate. Sometimes the ideal diameter wire may not be available, so a spring designer will use smaller or larger diameter and adjust the coil count accordingly.

Many racers mistakenly believe that wide spaced coils of a spring indicate a preferable spring. While a spring must have sufficient stroke capacity, it also must have sufficient material to absorb the load put onto it. If the spring’s material is not sufficient for the load put onto the spring, the material will become overstressed and the spring will take a set. Handling is affected, the reason is not always apparent.

Sometimes, because of the long stroke requirements for rates of springs, material strength must be sacrificed to achieve significant stroke. “Setting” or the pre-set of springs is a wise manufacturing policy; it can eliminate the potential for additional setting of a spring. Shot peening can enhance a spring’s durability.

CAN YOU DEPEND ON THE SPRING RATE STATED BY THE MANUFACTURER?

As a coil spring compresses, the inactive end coils gradually contact adjacent, active coils. The contact causes the active coils to deaden which increases the rate of the spring. The rate creep that results usually stops after the first inch of spring travel and does not appear again until spring travel approaches coil bind. It is important to realize that springs will pick up rate during compression.

Spring rates can vary by 5% from what is stated by the manufacturer. On a spring that is marked as a 200 lb. spring, the actual rate could be as low as 185 lbs. or as high as 215 lbs. Good spring manufacturers maintain accuracy within 2%, quality spring manufacturers maintain 1% accuracy.

SPRING TERMINOLOGY

SPRING RATE is normally measured in 1” increments of compression of the spring. For example a 200lb spring would take 200lbs of force to compress it 1”, 400lbs of force to compress it 2” and 600lbs of force to compress it 3”.

Its evenly spaced coils can normally identify a STRAIGHT RATE SPRING. It maintains the same spring rate progression for its full travel.

A PROGRESSIVE RATE SPRING can be identified by its tightly spaced coils on one end and wider spaced coils on the other end of the spring. As the spring compresses, the tightly spaced coils contact each other and are no longer active; leaving less coils available to compress. A 200-300lb progressive spring may rate 200 lbs at 1” of travel, 450 lbs at 2” of travel, and 750 lbs at 3” of travel. The beginning rate was 200 lbs and the ending rate was 300 lbs.

The FREE LENGTH of the spring (length of spring before installation) must be the correct dimension for the shock or fork that it is to be installed on. A spring that is too long or too short would not have sufficient range to allow for proper preload adjustment. The spring must also have enough travel capacity so that the spring does not coil bind before the shock or fork reaches full bottom. A spring with insufficient stroke capacity can damage the suspension components.

SPRING PRELOAD is the amount of tension that is applied to the spring from its full extended (before installation) length. This adjustment is very important for proper suspension action. Too little preload and the suspension will sag too much; steering control and handling will deteriorate. Too much preload will have a negative effect on the steering and handling of the bike and will make the ride harsh.

RIDE HEIGHT is the amount the vehicle settles with the rider on the bike in a normal seated position. Rear suspension is approximately 30% – 33%, the front is around 25% – 30% of the total suspension travel. This is why a 300 lb rider would require a stiffer rate spring and more preload to maintain the same ride height as a 150 lb rider.

FREE SAG or BIKE SAG refers to the amount the vehicle settles with no rider. This settling is about 6% – 10% of the total suspension travel. Too little bike sag can make the bike handle poorly and the ride harsh. Too much sag and you have less control over the bike, and you will lose travel of the suspension.