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.
Note:
Make sure the motorcycle is at its race weight. This includes all fluids
(transmission, radiator, fuel, etc.)
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 = 600mm
Example: B=
Rider on Machine =
500mm
Your Race Sag is =100mm
The Race sag is the difference between the Unloaded (A) and Rider
on Machine (B) measurement.
** Note:
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.
Recommended Race Sag measurements. **Note** Race Sag
Measurements are approximate and not exact for every rider.
125-650cc MOTORCYCLES 98-115mm
85cc MOTORCYCLES 85-90mm
65cc MOTORCYCLES 70-75mm
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. This is this measurement C.
Take
the unloaded measurement A and minus measurement C (Example
610mmA-580mmB=30mm free Sag)
**
Note: Standard 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 that's to stiff does not
allow the rear tire to catch traction and passes a more stiff feeling to the
rider. A spring that's to soft for your weight requires to much preload to
obtain proper race sag. This also leads to incorrect weight transfer and
balance. This will also lead to the rear end topping
out when the rider gets off the machine.
Spring Preload
Tip: 1 turn of preload either direction is about 3mm of change.
**
Note: 20mm or less free sag requires a stiffer spring rate.
**
Note: 35mm or more free sag requires a softer spring rate.
Spring
Rate 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 different 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 edge 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.
Fork and rear
shock springs for your dirt-bike are available for your weight and riding style.
Starting at $98.00
