# Bicycle Mechanics - SAG??? Damping?? Rebound? LONG

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View Full Version : SAG??? Damping?? Rebound? LONG

Carbon Blue
09-21-05, 03:38 PM
Hey whats up guys i finally bought my first fork and its a 2005 Marzocchi MX Pro w/ETA to replace the current fork on my Specialized. Ive been biking for about 3 years (mainly on a huffy, i know i know) and I finally upgraded to a 2005 hardrock specialized pro disc and do mainly cross country/trail riding with really small drops (1-2ft at the most which is really rare) and Iam pretty new to all these bicycle terms. (my huffy was basically a bike beat to death and never adjusted it whatsoever except for the brakes). Well with that said heres the situation that Iam in. Ive been reading the marzocchi instruction manual throughly and have noticed that they have included how to calculate SAG.

First it says "measure the the forks leg portion between the lower crown and the dust seal and take note of the value". Easy

Second it says to "sit on the bike and repeat the measurement and take note of the value." Easy again

So if I understand correctly its SAG=A-B

(fork is not installed on bike yet)

then the manual says "How to find the best SAG "

"the best sag corresponds to 15-20% for cross country forks and to 25-30% for freeride forks. In order to calculate the best SAG for your own fork, you will only need to do the following calculation."

"SAG=T x S (T= total travel; S=suggested sinking percentage)"

now heres where I get confused, when they say "total travel", do they mean total travel of the fork (105mm?) or the total SAG it attained after A-B?? and with the sinking percentage the smaller the percentage the less sag there is correct?

So say I get the desired sag which is X# after T x S. What am I supposed to do now? Is that the final number that the fork should sag in inches? I noticed there is also a diagram that shows the riders weight and how much positive air pressure i should use. I weigh in at exactly 167lbs in regular clothes,wallet etc.(with a full 3L camelback im probably at 170-174) and the manual states that I should be using 35-45lbs of "positive air pressure" and below that chart, it says "Preload Air pressure" 0-15psi. I thought positive pressure was the air preload? So am i pumping in 15psi into the air preload? or the 35-45lbs into the air preload?

So with the SAG question out of the way Ive just got a few other questions on Damping and Rebound. The manual keeps saying "Damping" I thought it was called "dampening" or is this a whole new different term?

Since i have a rebound adjuster on this fork (external and on the right leg) The manual states "When turning the adjuster clockwise you increase the rebound hydraulic braking, making the fork slower during the rebound phase."

So by turning the knob clockwise the fork becomes stiffer??

then it says "When turning the adjuster counterclockwise you decrease the rebound hydraulic braking, making the fork more responsive during the rebound phase."

The manual also states " If the adjustment is too reactive, the forecarriage becomes unstable and the mountain bike may swing."- so basically the knob is turned too far counterclockwise correct?

and again it says "On the contrary, a too slow adjustment makes the overcoming of multiple obstacles diffucult, where the suspension cannot go back to a complete extended position between an obstacle and the following one."- this is where i get confused again, if the adjustment was too slow wouldn't that mean the rebound is too reactive/soft/ since it cannot get back to the extended position?? I thought if you turned the knob clockwise you increase rebound which means that it gets to its fully extended position faster which means its stiffer??

As you can tell im greatly confused and that any help would be good. Ive searched but really havent gotten any straight forward answers for this rebound and damping or is it dampening subject.

Carbon Blue
09-21-05, 03:58 PM
oh and one more, do i just get a desired rebound by feel/preferance or is there another equation i have to use?

Waldo
09-21-05, 05:23 PM
Your sag (A-B) should be the 15-20% of 105 millis (so around 20 mm or so, about .8 inches). There's only one air chamber so I'm not sure where that question is arising. Perhaps you're seeing a section in the manual for one of the other forks in that series?
Rebound is personal-start out somewhere in the middle of the range, ride, adjust. Rinse and repeat. Stop when you've achieved sexy results. Same goes for your air pressure. Get your sag in the ballpark, ride, and tune.
It is actually damping, contrary to what many people believe.

hypersnazz
09-21-05, 05:36 PM
now heres where I get confused, when they say "total travel", do they mean total travel of the fork (105mm?)

Right.

So say I get the desired sag which is X# after T x S. What am I supposed to do now? Is that the final number that the fork should sag in inches?

Millimeters, probably.

I noticed there is also a diagram that shows the riders weight and how much positive air pressure i should use. I weigh in at exactly 167lbs in regular clothes,wallet etc.(with a full 3L camelback im probably at 170-174) and the manual states that I should be using 35-45lbs of "positive air pressure" and below that chart, it says "Preload Air pressure" 0-15psi. I thought positive pressure was the air preload? So am i pumping in 15psi into the air preload? or the 35-45lbs into the air preload?

There should only be one port, on top of the right leg. Fill this one to 35-45lbs.

So with the SAG question out of the way Ive just got a few other questions on Damping and Rebound. The manual keeps saying "Damping" I thought it was called "dampening" or is this a whole new different term?

Same.

Since i have a rebound adjuster on this fork (external and on the right leg) The manual states "When turning the adjuster clockwise you increase the rebound hydraulic braking, making the fork slower during the rebound phase."

So by turning the knob clockwise the fork becomes stiffer??

'Compression' typically refers to the downward stroke of the fork or shock. 'Rebound' refers to the return stroke. Slowing the return stroke means the fork will feel spongier on the upstroke, less like a pogo stick, but may not return fast enough on small, stuttery bumps.

then it says "When turning the adjuster counterclockwise you decrease the rebound hydraulic braking, making the fork more responsive during the rebound phase."

The manual also states " If the adjustment is too reactive, the forecarriage becomes unstable and the mountain bike may swing."- so basically the knob is turned too far counterclockwise correct?

So, more like a pogo stick.

and again it says "On the contrary, a too slow adjustment makes the overcoming of multiple obstacles diffucult, where the suspension cannot go back to a complete extended position between an obstacle and the following one."- this is where i get confused again, if the adjustment was too slow wouldn't that mean the rebound is too reactive/soft/ since it cannot get back to the extended position?? I thought if you turned the knob clockwise you increase rebound which means that it gets to its fully extended position faster which means its stiffer??

'Slower' does not mean the same thing as 'stiffer'. When they say 'slower', that's what is meant. Compress your forks. Let off the forks. The speed at which they *return* is what you're adjusting here.

As you can tell im greatly confused and that any help would be good. Ive searched but really havent gotten any straight forward answers for this rebound and damping or is it dampening subject.

You can't really hurt anything by turning knobs, so go out there and try 'em to see what they do. ;)

Carbon Blue
09-21-05, 07:29 PM
thanks alot for the help, you answered all of my questions. :D I just have to bring the bike in for its next tune up which is sunday and I should get the bike back monday afternoon with the new fork installed. Thanks again!

Carbon Blue
09-21-05, 07:47 PM
Your sag (A-B) should be the 15-20% of 105 millis (so around 20 mm or so, about .8 inches). There's only one air chamber so I'm not sure where that question is arising. Perhaps you're seeing a section in the manual for one of the other forks in that series?
Rebound is personal-start out somewhere in the middle of the range, ride, adjust. Rinse and repeat. Stop when you've achieved sexy results. Same goes for your air pressure. Get your sag in the ballpark, ride, and tune.
It is actually damping, contrary to what many people believe.

thanks, just want to run this over to make sure.

105mm (total travel) X 15% (suggested sinking percentage)= 15.75mm

so now when Iam on the bike, the bike should be sagging 15.75mm correct? and the way to achieve this SAG is either by adding air or releasing air through the air port in which I pump 35-45lbs of air correct? thanks again

Waldo
09-21-05, 09:22 PM
Yeah, that should be a good starting point. Experimentation is key when dialing in a new fork. They're just like women...everybody likes 'em a bit different.