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Dirt bike suspension tuning

Dirt bike suspension tuning by Mike Hobbs and Rick Johnson

Ρυθμίστε την αναρτηση σας (το περίφημο SAG)


Here's PART I of Too Tech's Suspension Tuning Tips.

Dialing in your bike's suspension: 7 easy steps.

The settings in this article are for a '97 YZ 250, GP Desert. Yours may be different


STEP 1: Measure suspension "RACE SAG" (Most important adjustment)

All measurements are made between the rear fender and the rear axle. The first measurement is made with the bike on a center stand with the rear wheel in the air.

The second measurement is made standing on the foot pegs with full equipment. The difference between these two measurements must be 3-3/4" for Short track and Supercross, 3-7/8" Natural terrain moto-cross, 4" Gran Prix and desert.



STEP 2: TUNE RACE SAG (The other "most important adjustment")


Adjust the forks to the standard height in the triple clamps before starting any adjustments.

Increasing the preload on your rear spring will decrease the Race sag.

This will raise the rear of your bike putting more weight on the front wheel and reduce the front-end rake. This will always make the bike turn sharper. However, if you tighten the spring too far it will make the bike twitchy and promote headshake.

Decreasing the preload on the rear spring will increase the Race sag. This will lower the rear of your bike, putting less weight on the front wheel and causing it to ride like a "chopper". This will reduce head shake, making the bike go straighter and be more secure in high speed sections.
However, if you loosen the spring too far the bike will be harder to turn.

To fine tune the spring preload (Race Sag), try tightening the rear spring adjusting nut 1/2" turn at a time and mentally note how much easier the front end will dive into a turn and hold the inside line. Continue this spring tightening until the bike becomes twitchy and unstable, or it feels like you're always pulling up on the handlebars. Measure and record your Race Sag.

Then try loosening the rear preload 1/2 turn at a time and mentally note how the rear end "Squats" down and traction increases as you exit each turn. When you reach the point of excessive front-end lift (wheelies) and loss of steering, or you begin to have trouble holding a tight turn, the spring is too loose and you have too much Race Sag.
Measure and compare these two extremes, then reach a compromise between them that balances "stability" and "tight turning".

Tune the front-end ride height to match the rear end! If the Race Sag compromise you determined above is close to the typical measurements listed above, your fork height adjustment in the triple clamps is probably about right. Raising the forks in the triple clamps will lower the front end making the bike turn sharper but will reduce high-speed stability. (Similar to increasing the rear preload.)

Lowering the forks in the triple clamps will raise the front end making the bike harder to turn, but will reduce high-speed stability. (Similar to lowering the rear preload.)

NOTE: Once you have established the best overall ride height front and rear, record these settings as your baseline. For added stability on a Desert or Gran Prix track, I always push my forks down about 1/8" to 1/4". For Moto-Cross I pull them back up to improve turning. To further improve turning on a flat Supercross style track, tighten the rear spring about 1 turn.



STEP 3: Break in the new suspension valves and oil

Leave the settings as received for at least 1/2 hour. Put the bike on a center stand and release the accumulated air from the front forks. Re-measure the rear shock sag to insure this critical adjustment is still 4 inches. Ride once again concentrating on any gross problems like suspension bottoming front or rear, definite harshness.


STEP 4: Adjust compression damping for bottoming

Rear shock: Increasing your compression damping (the screw on the shock reservoir), will slow down the compression stroke and decrease rear end bottoming. Turn you compression adjuster "in" (clockwise) to reduce bottoming. If you never bottom, try turning your adjuster "out" (counter clockwise) to soften the compression damping and use more travel.

Slight occasional bottoming is OK, but don't allow the bike to crash down when bottoming.

Front Forks: Increase the compression damping (the screw at the bottom of the forks) to slow the compression stroke and decrease front end bottoming. Turn your compression adjuster "in" (clockwise) to reduce bottoming. If you never bottom, try turning the adjuster "out" to soften the compression damping and use more travel.

NOTE: Softer, screw "out", settings provide a plush mushy feel which works well for cross country racers trying to go straight and conserve energy.
Stiffer, clicker "in", settings hold the suspension up and out of holes and provide more lift on jump take-offs. Additionally, body English and throttle changes transfer directly into the dirt instead of getting lost in a mush suspension.




STEP 5: Adjust compression damping front & rear

NOTE: Bring a small screwdriver with you and make adjustments at your test track.

It is important to make all damping decisions with the suspension hot and to immediately test the change.

Making damping decisions in the garage can lead to nasty surprises.

Letting your friends adjust your suspension is also a no - no.

If "bottoming" is noted at either end, the compression damping should be adjusted "in" (clockwise) to reduce the compression stroke. The front fork compression adjuster is the slotted screw at the bottom of the fork. The rear compression adjuster is the screw in the shock reservoir.


STEP 6: Adjust rebound damping front/rear. (Critical adjustment, change slowly)

If either front or rear tends to kick up, (rebound), more than the other after landing from a large jump, then more rebound damping is needed at that end. Adjusting the rebound damper screw "in" or "clockwise" causes more damping, which causes the suspension to return more slowly to its original ride height.

If the front end bounces up after landing from a jump, turn the slotted screw at the top of the forks "in" 1 click at a time to slow their return. If the rear end kicks up after landings, or kicks up side to side down high-speed straights, turn the slotted screw at the bottom of the shock "in" 1 click at a time, to slow the rear wheel return.

But remember, too slow a rebound setting causes "packing" because the suspension does not have time to rebound to its original ride height before you hit the next bump.

Rule Of Thumb: Run your rebound at both ends "faster" rather than "slower". When the bike in on the verge of, but not quite, kicking up after lands, the rebound is just about right.




STEP 7:
Balance front end and rear end static rideheight.

If the rear end squats under acceleration along with too much front-end lift and/or the bike doesn't want to turn sharp or easily enough adjust your rear sage to 3 - 3/4 inches. If the front end rides low, turns too sharp, and/or tends to Head Shake, try a combination of lowering the front forks in the triple clamps and adjust your rear sag to 4 - 1/4 inches.





PART II of Too Tech's Suspension Tuning Tips.

More 4 easy steps.

Let's pick up where we left in PART I: if "bottoming" is noted at either end, the compression damping should be adjusted "in" (clockwise) to reduce the compression stroke. Generally, the front fork compression adjuster is the slotted screw at the bottom of the fork. The rear compression adjuster is the screw in the shock reservoir.

Remember this! Making damping decisions in the garage can lead to nasty surprises.

Letting your friends adjust your suspension is also a no - no. Don't forget this!


From PART I, the bike spring rates were dialed in and the rebound and compression damping was adjusted.

Let's go further and fine tune the bike's suspension rebound and compression settings.


STEP 1: Adjust rebound damping front/rear. (Critical adjustment, change slowly)

If either front or rear tends to kick up, (rebound), more than the other after landing from a large jump, then more rebound damping is needed at that end. Adjusting the rebound damper screw "in" or "clockwise" causes more damping. This causes the suspension to return more slowly to its original ride height. If the front end bounces up after landing from a jump, turn the slotted screw at the top of the forks "in" 1 click at a time to slow their return. If the rear end kicks up after landings, or kicks up side to side while riding down high-speed straights, turn the slotted screw at the bottom of the shock "in" 1 click at a time. This slows the rear wheel return.

But remember, too slow a rebound setting causes "packing" because the suspension does not have time to rebound to its original ride height before you hit the next bump. Rule Of Thumb: Run your rebound at both ends "faster" rather than "slower". When the bike in on the verge of, but not quite, kicking up after lands, the rebound is set just about right.


STEP 2: Adjust rebound damping and stability for jumping.

This adjustment is extremely important and must be fine tuned by the rider very carefully. This adjustment determines how much time it takes the rear wheel to return to its original position after hitting a bump. In steps 1 & 2, (from PART I) you determined how much compression travel will be used as you hit each bump. The rebound damping must now be "tuned" to return the suspension to its original ride height before contacting the next bump.

If the rebound is too fast, the bike will bounce up after landing from a large jump, or kick sideways through rough sections. If the rebound is too slow, the wheel will not have enough time to return between bumps. This causes it to "pack down" becoming harsh and bouncy. "Packing" can occur as soon as the second bump. Experimentation is required to fine tune this adjustment. Stick a small screwdriver in your boot so you can make track side adjustments. Then ride and concentrate on the highest speed and most aggressive portions of your test track.


Front Forks: Start by speeding up the front rebound by turning the screw at the top of your forks "out" (counterclockwise) 2 clicks then ride your test track.

Continue turning the adjuster out until the bike kicks up after landings or bounces up for no reason. Record this setting for reference.

Then try turning the rebound "in" (clockwise) 2 clicks at a time until the front end begins to get stiff or your arms seem to be working harder.
These are signs of packing. Record setting. These settings define your rebound working range.

Personally, I prefer to run my rebound on the fast side. "Fast fork rebound will reduce headshake and arm pump."

Rear Shock: Start by speeding up the rear rebound by turning the screw at the bottom of your shock "out" counterclockwise) 2 clicks then ride your test track.

Continue turning the adjuster out until the bike kicks up after landings or kicks side to side. Record this setting for reference.

Then, try turning the rebound "in" (clockwise) 2 clicks at a time until the rear end begins to pound and get stiff.

If may feel like you have a flat tire, the rear is riding low, or like the rear is "dead". You will probably get tired faster.
These are signs of packing. Record the setting.
These settings define your rebound working range. I prefer to run my rebound as fast as possible without it kicking up or sideways.

NOTE: "Faster rebound settings will help you clear double jumps and ride aggressively." "Slower rebound settings conserve energy in deep sand and desert whoops."



STEP 3: Balance front end and rear end static ride height.

If the rear end squats under acceleration along with too much front-end lift, and/or the bike doesn't want to turn sharp or easily enough: Adjust your rear sag to 3 - 3/4 inches. If the front end rides low, turns too sharp, and/or tends to Head Shake, try a combination of lowering the front forks in the triple clamps and adjusting rear sag to 4 - 1/4 inches.


STEP 4: Balancing front and rear.

Regardless of personal preference on compression stiffness and rebound speed, both ends must be balanced and work together.

Compression Balance: The front spring and compression setting must coordinate with the rear spring and compression setting. If the front forks are too soft and plow through a whoop, but the rear end rides up over it, the bike will go into the "endo" position. To cure this, you would try to stiffen the front to make it ride up and over this bump to match the rear end. First, try a combination of turning the fork compression adjuster screw in, adding 1/4" fork oil, adding preload to the front fork springs, and pulling the fork tubes down in the triple clamps. Also, try speeding up the front rebound clicker "out" 1 or 2 clicks. This makes the front end kick up after this bump. When you reach the limit on making the front stiffer, you should try making the rear end softer. Try a combination of turning the shock compression setting "out", and reducing rear spring preload. Also try slowing the shock rebound, clicker "in" 1 click, to make the rear stay down after the bump. Reverse this logic if the fork is stiffer than the rear.

Rebound Balance: The front and rear rebound settings must coordinate to throw the bike up level on jump take-offs. (First the compression balance adjustments above must be made.)
If the front end continuously jumps higher than the rear, try a combination of slowing the fork rebound, clicker "in" 1 click, and speeding the rear rebound, clicker "out" 1 click.


GENERAL NOTE: Heavier riders, very aggressive riders, and desert riders will usually prefer heavier spring rates.


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