rebound bleed

Joined
Jan 2, 2001
Messages
416
Likes
0
#1
Lately i read some more about rebound bleed. Jeremy said something about it, and today Marcus mentioned it.
Can somebody explain some about this? the way it is set-up?
and the why offcourse?
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#2
I feel that all the suspension fiddlers have read this topic, but nobody has reacted.
Is it because nobody has experience with it, so you can't react or..
For stutter bumps is it not of the biggest importance that your fork is coming back quikest to react for the next (little) impact.
Or is everybody dealing with this by using two-stage stacks. Light low-speed and stiffer high-speed stacks.
pls try one more time
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#3
georgieboy i was hoping someone else would reply as you must get bored with my opinion on things.

here goes, on suspension we have 3 main speeds we can alter-bleed , low speed and high, lets not consider mid as according to some dyno graphs is almost impossible to alter.

Bleed is normally on very slow movements-like riding in the pits etc, once you get any pace then you are into the low speed stuff(remember we are talking shaft/fork speeds not bike)then as you hit sharp bumps at decent speed you are into high speed movements.

Bleed is normally a hole in the piston that bypasses the shims.More bleed needed-bigger hole.
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#4
I am sincerly happy with yr input, and with everybody elses for that matter.
I can offcourse just alter my shim stack and see what happens, but beforehand, i appreciate everyones input. So thx for the replie, Marcus.
Regarding that free-bleed as being a hole in the piston. I have seen that on one of my pistons. But not on all of them. You refering to the stutter bumps, as being high speed related(if i read yr reply correctly), I agree with you. But that is the comp side of it. To get them back quickest, rebound must react quick as well, by letting oil bypass the shims. I suggest by creating free-bleed, more that that tiny hole in the piston, but you suggest otherwise?
 
Joined
Nov 8, 2003
Messages
200
Likes
0
#5
Bleeds are used for a variety of reasons. Some times to assist with the bleeding of the cartridge and sometimes to avoid cavitation by allowing the area behind the rebound piston to quickly refill with oil on the compression stroke. If the bleed is being employed specifically for the purpose of tuning rebound damping then it is usually to correct an imbalance between high and low speed damping that can not effectively be tuned out via the shimstack. Remember your rebound adusting circuit is nothing more than a variable bleed.
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#6
Thx Terry for sharing yr thoughts on this aswell.
I must clarify something first.
Mentioning rebound bleed, i mend to say, free lift. like on mv comp stacks.
The reason that i am thinking of using a free lift(rebound bleed) is to enable the suspension to quickly return to their full length. So it is not so much to fix an imbalance, although you cld mention it that way. I just like to know if this is the way to go, or that it is better to go the dual-stage path without any free lifts. Or maybe a bit of both.
Offcourse with full impacts returning i still need enough rebound overall.
So i hope that didn't confuse you guys to much.
I have read that Jeremy mentioned it a few times, especially for the stutter bumps.
 
Joined
Nov 8, 2003
Messages
200
Likes
0
#7
Wether you create a bleed by drilling a hole or placing a clearance shim on your stack you will still end up with a similar situation. A free flow of oil will result until pressure overcomes the resistance of the shimstack and it begins to bend. The advantage of the clearance shim is that it is very tunable by adjusting diameter and thickness and it will usually only work in one direction(similar to a one way valve). Unless of course your shim is close to the diameter of the piston orifice arrangement. You guys are placing a lot of thought to your various situations and seem to be getting deeper into things than perhaps you need to be. Remember the basics of hydraulics. When pressure is applied to a fluid, it is equal and undiminished in all directions. Midspeed, highspeed, lowspeed, midstroke, initial, endstroke. All areas are constantly subject to the same amount of force. As one valve bends, pressure is equalised in all areas. The same pressure is applied to an orifice as a shimstack. Naturally the oil (or pressure) will take the path of least resistance. The capacity for an orifice to flow oil is finite. As soon as that capacity creates sufficient resistance to equalise the resistance of the shimstack, the shims will bend. Balance is the key.
 
Joined
Jan 2, 2001
Messages
416
Likes
0
#8
you may say that i am creating a path of least resistance for the oil by creating a freelift at the rebound stack. By doing so, with small, high speed hits(stutter bumps) small quantities of oil can flow freely so creating no resistance, rebound is returning quickly to full length. If speed increases with bigger hits, oil forces are equally high, bending the shimstack, so damping increases likewise.
I strongly have the feeling that rebound is the culprit with small highspeed impacts, creating packing.
But perhaps i will create a pogo effect, i just have to see, i guess.
Terry, by the way, thnks simplifying things a bit! thnks for joining.
Hee Marcus an other one that replied. wink
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#9
Im glad terry has entered the conversation as he has made some good points i never thought of.We are all learning:)
 
Joined
Apr 19, 2000
Messages
456
Likes
1
#10
One other thing to keep in mind is that bleed works in both directions. You drill a hole in your piston and it will affect both compression and rebound.