Tips
Most Common Mistake...
All but a few riders can really feel their bike bottoming. Most riders think the damping or the linkage is too harsh. But what really is happening is they are running too little preload on the spring or to soft of a spring and using the last half of the stroke only... Setting correct spring rates with correct preload and race sag is very important to your bikes setup...
Setting Shock Spring Preload and Race Sag
The adjustment procedure that follows establishes the correct starting point for any suspension tuning. This will guide you to the proper spring preload adjustment and spring selection for your weight. Damping adjustments comes later. The first step toward determining proper suspension adjustment is to set the rear spring preload so the proper race sag is achieved.
Pro-Motion INSIDE TIP: The machine should be to normal racing weight. This includes the correct amount of fuel for racing, transmission oil and coolant levels.
Setting Race Sag
1.) Measure the distance from the center of the rear fender to the center of the chain adjuster block... This is your unloaded measurement. We will call this measurement A.
A= Unloaded measurement (machine on the stand with both wheels off ground)
2.) Now measure the same 2 spots with the rider on the motorcycle with both feet on the pegs. (This requires 2 people) This is your loaded measurement B.
Example: A= Unloaded Measurement = 610mm
Example: B = Rider on machine = 510mm
Your Race Sag is = 100mm
The Race sag is the difference between the Unloaded (A) and Rider on Machine (B) measurement.
Pro-Motion TESTING TIP: Adjust spring preload as necessary to obtain the correct handling results. Remember more preload improves turning character of machine but makes the machine a little less stable...
Pro-Motion Recommended Race Sag measurements...
65cc MOTORCYCLES 70-75mm
85cc MOTORCYCLES 85-90mm
125-650cc MOTORCYCLES 98-115mm (Pro-Motion recommends a starting point of 100mm.)
CHECKING FREE SAG MEASUREMENT.
Now you have to compare the rear suspension sag under the weight of the sprung portion of the machine itself. (without rider) Motorcycle with both wheels on ground. (no stand) Take this measurement. We will call this Measurement C
Now take the Unloaded measurement A and minus measurement C (Example 610mmA-580mmB=30mm free Sag)
(STD FREE SAG is from 20-35mm) If after setting the spring preload to your race sag and the bikes sag more than 35mm in the rear under its own weight, the spring is to stiff for your weight. A spring thats to stiff does not allow the Rear Tire to Catch Traction and passes more stiff feeling to the rider. A spring thats to soft for your weight requires to much preload to obtain proper race sag. This will lead to the rear end topping out when the rider gets off the machine.. This also leads to incorrect weight transfer and balance..
20MM OR LESS FREE SAG REQUIRES STIFFER SPG RATE.
35MM OR MORE FREE SAG REQUIRES SOFTER SPG RATE.
Pro-Motion Spring Preload Tip: 1 turn of preload either direction is about 3mm change
Spring Rates Info:
If you are lighter or heavier than the average rider and cannot set the proper ride height without altering the correct spring pre-load, consider a differenr rate spring.
A spring that is too soft for your weight forces you to add excessive spring pre-load to get the right race sag and, as a result, the rear end of the machine is raised. This can cause the rear wheel to unload too much in the air and top out as travel rebounds. The rear end may top out from light braking, or kick sideways over lips and square-enge terrain. It may even top-out when you get off your machine.
Keep in mind that a properly adjusted suspension system may bottom slightly every few minutes at full speed. Adjusting the suspension to avoid this occasional bottoming may cost more in overall suspension performance than it is worth.
A spring that is too firm for your weight will not allow the rear tire to hook up under acceleration and will pass more bumps on to you!
Pro-Motion Hot Tip:
For ease of releasing air pressure after the forks are installed, loosen the lower pinch bolts and position the outer tubes so that the pressure release screws are in front of the rebound damping adjusters.
note: Over tightening the pinch bolts can deform the outer tubes. Deformed outer tubes must then be replaced. I cannot stress how important it is to torque your pinch bolts to the manufactures specs!