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Proper Setup for the 2013 KX450F KYB PSF Fork - More Motocross Videos
Setting the proper race sag is the most important adjustment you
can make. Without the sag properly set a proper balance cannot be obtained.
Race sag refers to the amount of rear wheel travel used by your bike at rest
with rider on board. As a general rule of thumb, the race sag should be about
one-third of the maximum travel. Ride height is changed by adjusting the rear
suspension spring pre-load.
Spring Preload &
Race Sag Adjustment
The following adjustment procedure establishes the correct
starting point for any suspension tuning - the proper rear spring preload
adjustment for your specific needs. Your bike should be at normal racing
weight, including fuel and engine oil. You should wear all your normal
protective gear. To calculate the proper adjustment, it's necessary to measure
between two fixed points - from the fender down to the axle, for three
rider): Bike on a stand with rear suspension fully extended
Loaded - with rider:
Bike on the ground
Loaded - without rider:
Bike on the ground
Calculating the Race Sag
Support your bike on a stand with the rear wheel off the ground.
Measure the distance from a fixed point on the rear fender to the center of the
axle. Write this measurement down. Remove the stand, with a couple of helpers’
available, sit in a neutral position (center of hip over the foot pegs) on the
seat. Ask one helper to steady your bike perfectly upright so you can put both
feet on the pegs. Bounce your weight on the seat a couple times to help the
suspension overcome any sticking action and settle to a good reference point.
Ask the other helper to measure the "loaded - with rider" distance.
To calculate the race sag dimension, subtract the "loaded -
with rider" dimension from the "unloaded" dimension.
Unloaded - 671mm (26.4")
Loaded w/rider - 568 mm (22.4")
Race Sag = 103 mm (4.0")
Adjust spring preload as necessary to obtain the desired handling
Decreasing the race sag
dimension (i.e. 98mm, 3.9") improves turning ability for tight terrain at
the cost of slightly reduced straight line stability.
Increasing the race sag
dimension (i.e. 108mm, 4.3") may improve stability on faster terrain with
less turns, but will reduce turning performance slightly
The ideal race sag (ride
height) will vary with bike model and rider preference (100mm-105mm is a good
starting point). Individual preference may produce race sag from 95mm-115mm. It
is important to know your ideal race sag measurement before changing spring
preload. Different abilities, riding styles, and measuring techniques will vary
the ideal race sag among individual riders.
Unloaded - 671mm (26.4")
Loaded w/o rider - 631mm (24.8")
Free Sag = 40mm (1.5")
Free sag indicates the distance the rear suspension should sag
from the weight of the sprung portion of your bike. To calculate the free sag,
subtract the "loaded - without rider" dimension from the
"unloaded" dimension. Do this with your bike set at the standard race
With the spring preload set to obtain the proper race sag, the rear
suspension should sag 25mm to 45 mm. If the rear of your bike sags less than 25mm
from its own weight, the spring is too soft for your weight. Too much pre load
is needed to obtain the proper race sag adjustment.
If the rear of your bike sags more than 45mm from its own weight,
the spring is too stiff for your weight.
If you are lighter or heavier than the average rider and cannot
set the proper ride height without altering the correct spring preload,
consider an aftermarket spring.
A spring that is too soft for your weight forces you to add
excessive spring preload to get the right race sag and, as a result, the rear
end 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-edged terrain.
Because of the great absorption quality of the shock bumper
rubber, it may be difficult for you to notice when your bike's suspension is
bottoming out. Some riders may think the damping or perhaps the leverage ratio
is too harsh and in reality, the problem is most likely insufficient spring
preload or a spring that is too soft. Either situation prevents utilizing the full
potential of the suspension.
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 it will pass more bumps on to you.
This is a basic guide line. Contact us a more detailed analysis and advisement.
Balance front end and rear end static ride height
- If the rear end squats under acceleration along with too much front-end lift, or the bike doesn't want to turn sharp enough, tighten your preload by adjusting your rear sag -5mm (example: 100mm adjust to 95mm). (Note: Raising the rear end helps turning)
- If the front end rides low, turns too sharp, and/or tends to Head Shake at high speed, try a combination of lowering the front forks in the triple clamps and loosen your rear sag to +5mm (example: 100mm adjust to 105mm). (Note: Raising the front and lowering the rear helps stability)
Adjust Rebound damping front/rear. (Adjust 1or 2 clicks at a time)
- If either front or rear tends to kick up (rebound) faster than the other does after landing from a large jump, the rebound is not balanced front to rear. You can slow down the end that kicks up or speed up the end that is hanging down.
- Adjusting the rebound screw "in" (clockwise) creates more damping, causing the suspension to return slower to its original ride height. If the front end bounces up after landing from a jump, turn the slotted screw at the bottom of the forks "in" 1 click at a time to slow their return. If the rear end kicks up after landings or kicks up on high-speed straights, turn the slotted screw at the bottom of the shock "in" one click at a time to slow the rear wheel return.
- Remember; too slow a rebound setting causes "packing" because the suspension does not have time to return to its original ride height before you hit the next bump. This causes the second bump to feel stiff and causes the rider to tire quickly. (Note: that being soft or stiff on compression will cause kicking as well.)
Adjust compression damping front & rear
- If "bottoming" is accurse at either end, the compression adjuster should be turned "in" (clockwise) to stiffen the compression stroke. The front fork compression adjuster is the Slotted Screw at the top of the fork. The rear shock compression adjuster is the Slotted Screw and the Hex Nut in the shock reservoir
- If either end is stiffer than the other, turn the adjuster “out" (counter clockwise) at the stiff end. This will soften the stiff end making it more compatible with the other “softer” end.
Note: On hard pack tracks, set your rebound at both ends "slightly faster” to follow the terrain.
On deep sand tracks, set your rebound “slower”, especially at the rear, to prevent bouncing out of the rollers.