4Strokes.com Tech: Fork Oil Adjustment - By Michael Hetrick
First of all, I drain the forks and then accurately set the initial oil level. DON'T BE AFRAID OF THIS STUFF!!! IT IS REALLY QUITE SIMPLE!! Just follow the directions in your service manual. If you don't have a manual - BUY ONE. While I have the fork open initially, I use a 50 cc syringe from a farm supply store and add oil with the syringe until I measure a 5mm level change (with the spring *IN*). I then log this value, in cc's, down in my manual. This will allow me to accurately set my forks over and over in the future.
Then, AND THIS IS IMPORTANT!!, I pick a day to play with the suspension. I play with suspension and NOTHING ELSE!!! No play ride after or anything else to detract from concentrating on the task at hand. If you have a buddy that is interested, this is a GREAT way for both of you to learn about your suspension together. Misery loves company! This is REALLY important and way too many trail riders simply don't do this and are wasting the capabilities of their suspension because of it. It is not voodoo or even hard. You just need to go out and play with the settings.
I go out and find a test area that has some whoops, rocks, and what have you. Whatever is typical for your riding area, but an area that AT LEAST has something from everything you are likely to come across on your daily rides. YOU have to be the judge of what is important to you. For example, I do fine at speed, but falter at real slow technical stuff. Therefore, my trail bike is set up to give me the best results where I am the weakest. My race bike is set up to take advantage of what I am fastest at.
I then set all the suspension to the factory defaults other than spring rates, which have to be changed if you are considerably larger or smaller than average. I have found that I like it pretty plush on the trail and therefore set my sag at about 115 mm's. I then make a few test runs to set a baseline, i.e.- get a feel for the bike.
Then, writing down all my impressions and observations in a logbook (IMPORTANT), I start with the fork rebound and dial it ALL THE WAY OUT. I ride the bike, and note the effects. I then dial the rebound ALL THE WAY IN. Ride and log. Then I set the rebound to the factory default. Then I run the compression ALL THE WAY OUT. Ride and log. Then set the compression ALL THE WAY IN. Ride and log.
Repeat this for the shock. You may also want to ride with rebound AND compression maxed to each direction. And also with the rebound maxed one way and the compression maxed the other. Do this for both the forks and shock.
I then do the same as above, but only varying the clickers 3 clicks in each direction. IMPORTANT NOTE: You need to do the max adjustment cycle BEFORE the three clicks at a time adjustment cycle. The max adjustment cycle teaches you what gross effect the change will make. If you do the 3 clicks cycle first you will not have felt the gross change of the max cycle and will not be able to tell the difference of only 3 clicks. After the gross adjustment phase you will be more savvy and be able to identify what adjustment is doing what.
One of the finer adjustments is the oil height adjustment of the fork. This adjustment changes the volume of air that is in the leg. This air works as a spring when the fork collapses, so by changing the oil height, you change the amount stiffness of this 'air spring'. Obviously this spring is most pronounced that the end of the fork travel and nearly non-existent at the beginning of fork travel.
To adjust the fork oil, I found it easy to use a 50 cc syringe from the farm supply store with as big a needle as will fit to fill or draw oil from the bleed holes in the fork caps. As before, you need to add a set quantity to each leg, then ride and log. With some manipulating you can lay the bike on it's side and draw oil out if you want to return to factory settings or a lower level than you currently have.
Now that you REALLY know what the adjustments do on YOUR bike, Go back to the stock settings and ride the test course again. Think about what you did not like and see if you can adjust it out. The first couple of times you will probably get the bike all out of whack. Don't stress out, just set everything back to stock and try again. In no time you will be the envy of your buddies and the local suspension guru.
IMPORTANT- Note how adjusting the fork can affect how the back end performs and how adjusting the shock OFTEN throws the front end out of whack. You will always have to adjust for BALANCE. Seldom with dialing in a few clicks on one suspension component suffice. Often you will have to adjust one to solve a problem, and then the other end to balance it out.
One final note. Standard type forks are not what is considered 'stiff'. Due to this, they are more susceptible to imbalances in the oil levels and settings for each leg. If your bike tends to exhibit some head shake in stutter bumps or especially sand, check to make sure your rebound and compression settings are the same for each leg. Most of the time the settings are the same and the problem ends up being an imbalance in oil levels between the legs.
This method has served me well over the years. I hope it can be of some use to your readers.
Credits: Article written and submitted by Michael Hetrick and edited by 4Strokes.com.