Does Rebound effect compression?

Live2DieTrying

Likes Bikes and Dirt
I am about to recieve a pair of forks, and i will be changing the oil before anything. Nowi've already been and purchased some 5wt oil, and i have approx. 8wt in my forks at the moment.
(my current fork is a 98 junior t, and i'm pretty sure it has rebound adjustment, but the caps have little C's on the top. anyways this isn't imprtant)
I read a suspension thread a while ago, and got a very rough idea that rebound can effect compression, but i didn't find myself a deffinate answer...

I'm not really sure how i like my reboud, but i'd say that i don't like it slow (this is why i got the 5wt)
So, by altering the weight of the oil, does it effect how the fork compresses, or just how it rebounds..?
 

S.

ex offender
For practical purposes, rebound ADJUSTERS do not affect the compression and vice versa (in actual fact there may be a very tiny effect due to backflow through each damper on its reverse stroke). Only the Mojo aftermarket kits have a common compression/rebound adjuster that I know of.

However - changing the oil, if that leg contains both rebound AND compression dampers, will affect BOTH dampers. If you have external adjustments for each this isn't a big deal, if you have only one adjuster (presumably rebound) then use oil weight to control your compression and just set the adjuster up as necessary to control the rebound. What forks are they, by the way?
 

Pixsoul

Regulating n00bs
Repression

Yeah if both compression and rebound are in the same leg than the oil weight will affect both.

Rockshox are working on a single rebound and compression unit all in one, its called "Repression". lol.
 

Binaural

Eats Squid
Changing the oil thickness will change the rebound and compression damping. However, this is not going to massively effect the performance of your forks since these two damping types tend to be adjusted in tandem anyway. If you run heavy rebound damping you would generally run heavier compression damping as well to prevent packing up. If you set your fork up with quick rebound for a lively feel, you would usually also run lighter compression to complement this.

As a side note, I have always found my forks feel best when the compression and rebound settings are not way out of sync with each other. I used to run my forks with max rebound and min compression damping on the basis that extra compression damping = extra force applied during hit and high rebound damping = easier recovery. However, my latest tune is now light compression with light rebound and the bike feels much livelier without being inclined to get out of hand on big hits.
 

ajay

^Once punched Jeff Kennett. Don't pick an e-fight
Binaural said:
If you run heavy rebound damping you would generally run heavier compression damping as well to prevent packing up. If you set your fork up with quick rebound for a lively feel, you would usually also run lighter compression to complement this.

As a side note, I have always found my forks feel best when the compression and rebound settings are not way out of sync with each other. I used to run my forks with max rebound and min compression damping on the basis that extra compression damping = extra force applied during hit and high rebound damping = easier recovery. However, my latest tune is now light compression with light rebound and the bike feels much livelier without being inclined to get out of hand on big hits.
This is how the mojo stuff is set up... :)

S. - thats how i like my forks, which is why i guess i like the mojo set up - ie. no placebo effect here mate;) [/off topic]
 

S.

ex offender
ajay said:
This is how the mojo stuff is set up... :)

S. - thats how i like my forks, which is why i guess i like the mojo set up - ie. no placebo effect here mate;) [/off topic]
Whatever works for you :)
 

S.

ex offender
Oh ok. In that case it's just a delusion that there's no placebo :)

Seriously though - the IDEA behind the Mojo kit is not way off the chart, and yes running heaps of rebound with little compression (and vice versa) is generally not the ideal setup, but it doesn't allow you to play with the fork's ride height in the rough or dial out dive or anything like that without affecting other things. If you don't mind that then cool, it'll be fine. If you're as anal as I am then chances are you won't be a huge fan :)
 

Binaural

Eats Squid
Can't the Mojo cartridges adjust rebound and compression separately? That doesn't sound so good. Generally you adjust them so they are in the same sort of range, but there are times you want to have them out of step. For example, on long, fast but rattling courses (Thredbo, for example) where bottoming or wallowing is not a problem but hand fatigue is, I tend to run low compression and high rebound to spare the hands a bit. The bike tends to settle in corners a bit as well, which suits the high, hard berms they have there.
 

S.

ex offender
Binaural said:
Can't the Mojo cartridges adjust rebound and compression separately? That doesn't sound so good. Generally you adjust them so they are in the same sort of range, but there are times you want to have them out of step. For example, on long, fast but rattling courses (Thredbo, for example) where bottoming or wallowing is not a problem but hand fatigue is, I tend to run low compression and high rebound to spare the hands a bit. The bike tends to settle in corners a bit as well, which suits the high, hard berms they have there.
Yeah they have a common bleed adjuster; both rebound and compression are adjusted simultaneously. If you're capable of pulling forks apart and revalving them (ie actually know what you're doing with the shims which 99.9% of people won't) and you have the gas adaptor thing then you can revalve them yourself, but if not you're stuck with the preset rebound:compression settings.
 

scblack

Leucocholic
Binaural said:
Can't the Mojo cartridges adjust rebound and compression separately? That doesn't sound so good. Generally you adjust them so they are in the same sort of range, but there are times you want to have them out of step. For example, on long, fast but rattling courses (Thredbo, for example) where bottoming or wallowing is not a problem but hand fatigue is, I tend to run low compression and high rebound to spare the hands a bit. The bike tends to settle in corners a bit as well, which suits the high, hard berms they have there.
Just the one adjuster, and it does work very well.
 

Live2DieTrying

Likes Bikes and Dirt
S. , they are white brothers UD150's (i know they are old, but my lack of money never gets me much for my bike)
I pulled them apart as soon as i got them (today) and they seemed to have no oil in them at all...
The right leg is pretty much empty apart from the rbound adjuster (external knob...) and it looked a lot different from my old old marzocchi's.
The left leg has a big srping in it, and a (cartridge?) inside or below the spring... i couldn't get them fully apart, and i didn't want to put too much force on anything, so i left it at that.
would there be oil inside the cartridge..? i can here an oily noise when i push down on them.
 

Cave Dweller

Eats Squid
Binaural said:
Changing the oil thickness will change the rebound and compression damping. However, this is not going to massively effect the performance of your forks since these two damping types tend to be adjusted in tandem anyway.
Hmmm...... im thinking it would effect the performance alot actually.

Putting heavier oil in will slow down the rebound and compression circuits as you note, but backing the compression and rebound circuits out to compensate for more viscous oil won't achieve the same performance level as you are pushing more oil through the bypass circuit and less pass the shim and valve, in effect, turning the fork into a ported damper (think ssvf, fluid flow etc), relying on the viscosity and velocity of the oil through the bypass to provide damping. Dodgy way to do it IMO.

Better performance will come from running lighter oil and actually using the compression and rebound circuits, thats what you paid all that money for.

If you find the compression and rebound is off, in my opinion (and if its possible, can't do this with marzocchi dampers), you should put in some shims which do not deflect so easily and keep the oil weight light.
 

S.

ex offender
Cave Dweller said:
Hmmm...... im thinking it would effect the performance alot actually.

Putting heavier oil in will slow down the rebound and compression circuits as you note, but backing the compression and rebound circuits out to compensate for more viscous oil won't achieve the same performance level as you are pushing more oil through the bypass circuit and less pass the shim and valve, in effect, turning the fork into a ported damper (think ssvf, fluid flow etc), relying on the viscosity and velocity of the oil through the bypass to provide damping. Dodgy way to do it IMO.
I think you'll find it's actually the other way around - the needle valve/ported valve is the LSC component, and oil will flow through that UNTIL enough pressure is generated to push the shims/HS valve open. In other words, the LS is the primary circuit and the HS is the secondary, parallel circuit. The ported damper is a fixed (hydraulic) diameter at any given adjustment point, regardless of any other factors, and running a thicker oil will simply force the shims open at a lower speed as the pressure generated due to the resistance through the LS port becomes higher faster, and the shims will also open further at any given speed where they are open. In this respect it would lower the (relative) HS "blow-off" point.

Cave Dweller said:
Better performance will come from running lighter oil and actually using the compression and rebound circuits, thats what you paid all that money for.

If you find the compression and rebound is off, in my opinion (and if its possible, can't do this with marzocchi dampers), you should put in some shims which do not deflect so easily and keep the oil weight light.
I have found that lighter oils do seem to run smoother, but I think that's more to do with flow pressure consistency due to turbulence (lower viscosity = higher Reynolds number = more turbulent flow = less separation around port/valve edges and shims) rather than more oil being forced through the LS circuit.
 
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