[jcook90]

i was reading marzocchi's website about the 888RC2X's and on the page for the fork it says it has low speed compression via the RC2, and highspeed compression with the X. however in the manual for the fork it says the X-cartirdge only controls the dampening towards the end of the travel which seems kinda similar to answer/manitou's SPV i think. anyone know which it is, either high/low or just harder at the travels end?

 

[davep]

It is 100% different than SPV!!!


It controls low speed by closing off bleed ports at the bottom of the damper and also provides an increase in end of stroke damping via the same mechanism.

 

[jcook90]

yeah but then is there also highspeed compression that makes it harder throughout the entire stroke of the fork?

 

[vitox]

no, the x is more of a hi speed compression feature but the freebleed ports in the cartridge make it work mostly in the lower third of the travel.
the bottom adjuster in the rc cartridge could fit the term low speed compression better as it works more or less in the complete speed and travel range.

 

[Biscuit]

SPV is a "platform valve" that prevented the fork from moving. It took a bump to break it loose. Basically adding "stiction".

RC2x:
R = rebound adjustment; how fast the fork returns to the starting position after a hit.

C1 - Low speed compression = general compression for most bumps and stutters; This is the compression most forks/shocks have and affects traction the most; Most people run this relatively open depending on your style/weight.

C2x - High speed compression = is basically when you hit something hard and big, like a big rock, curb or land a drop. The fork is compressing with a much greater velocity (i.e. high-speed); This compression mostly kicks in at the end of the stroke to keep the fork from bottoming out.

The advantage of RC2x is you can run open compression, which begets better traction, and adjust the high-speed compression to keep from bottoming out constantly.

 

[jcook90]

ahh thanks, so its basically what they say in the manual about highspeed being at the end of the travel. that sounds kinda like how on the foes mono u can run 2 different spring rates in the rear to make it soft off the top, then harder towards the travels end (dont yell at me if i'm wrong). i always thought highspeed worked from the start of the travel and just make the whole stroke harder but i guess not. thanks

 

[davep]

ahh thanks, so its basically what they say in the manual about highspeed being at the end of the travel. that sounds kinda like how on the foes mono u can run 2 different spring rates in the rear to make it soft off the top, then harder towards the travels end (dont yell at me if i'm wrong). i always thought highspeed worked from the start of the travel and just make the whole stroke harder but i guess not. thanks

Yes.....Kind of. The way that you are thinking of it is correct, it is just that damping and springs do completely different things.

 

[jcook90]

yeah i know, the dampening makes it harder towards the end of the travel, but does it depend on the speed or will it always ramp up the compression towards the end?

 

[Biscuit]

Yes.....Kind of. The way that you are thinking of it is correct, it is just that damping and springs do completely different things.

I was biting my tounge

You've got the idea JCook, just your terminology is a little off (technically). Springs=Springs, Damping=Damping.

Basically the spring is ONLY referred to as the coil or air chamber that provides the.. er.. spring.
The damping, valves, shock, whatever is all the valving and control mechanisms we discussed earlier that make a shock so much more than just a spring.

Spring provides resistance and pushes back. A 300lb spring takes 300lb's to compress the spring 1".

Your damping (high speed, low speed, etc) controll how quickly the spring can compress/decompress.

 

[jcook90]

yeah i had it in my head just didnt know the words for it. i was thinking with the whole foes spring part about how w/ the 2 springs u can have the shock become alot harder towards the end of the travel, and was thinking that its kindof similar (except for them being springs) to how the highspeed dampening in the 888 is supposed to work by making the compression harder towards the end of the travel but it doesnt use different springs it uses the dampening to do it (not springs). i think i got it now, and dont tell me i'm wrong cuz i just want to get my 888 and be happy lol. actually go ahead and correct that if u want to cuz i kinda wanna learn this. thanks for ur help though

 

[Biscuit]

Get the 888. Its the best for out ther IMO. Especially when you consider how cost effective it is compared to others of it's caliber.

And FYI, I stated earlier that a 300lb spring will require 300lb's of force to move it one inch. There is such a thing as a progressive spring (not the company, its a term) which requires more force to move the farther you compress it.

For example: the 300lb spring stated above would require 600lb's to compress it two inches. This is called a "linear" or "straight rate" spring.
If the spring is "progressive" or "rising-rate", it would require 300lb's for the first inch, then say 350lb's for the second inch.
A "regressive" or "falling-rate" spring is the exact opposite of a progressive spring.

$0.02

 

[jcook90]

yeah the bike i'm getting is coming w/ one on it.

thats pretty cool about the springs, i always wondered about that. can you get them for forks? and what purpose would a regressive spring serve? it'd seem like you'd just sit on it and if u could compress it an inch to begin with then you'd just use up all spring's stroke

 

[Lejk]

Do you guys have any thoughts about the airsprung 888 (SL ATA or what it's called)?

I was thinking about going for this fork instead of the RC2X, to save some weight, but do you think that I'll miss that high-speed compersion? Or is the advantage of the RC2X only that you are able to tune the high-speed comp by yourself?

 

[RMR]

It's my first post and I'm going to see if I can make a good impression by doing some grave digging. umm...sorry about that.

Regarding a 2006 888 RC2X:

I'm still trying to get clear on the function of the two compression adjustments, despite Biscuit's explanation above. The lingering confusion is because Biscuit's description of LS and HS compression damping is somewhat inconsistent with how most damping circuits operate.

Typically, HS and LS are just sets of shims in the stack; the LS set are easy to open or are always open and are the ones active when pedaling and when the bike is responding to the overall contours of the trail. When you hit something - rocks, roots, the ground after a landing, etc. - you blow open the damping and get into the HS circuit.

Stutter bumps are too sharp for LS compression and most bumps, which Biscuit says are handled by LS, are usually handled by HS. Generally speaking, LS is attitude control and keeps the bike level, while HS controls impact management.

So, does this mean the "normal" (bottom-mounted) compression damping adjustment actually works on the HS system and the X adjuster is just position sensitivity, analogous to a DHX 5's bottom-out adjustment cap (the one you rotate with a 4 mm hex)? Alternatively, is it true that the "normal" compression adjuster really is a LS adjuster (analogous to ProPedal) and the X is a HS adjuster (an adjustment the DHX 5 doesn't have) with built-in position sensitivity?

 

[Udi]

RMR - you have the right idea, biscuit's definitions are pretty well incorrect (or misleading at best).

LSC controls bike attitude at low shaft speeds (cornering, g-outs, jump takeoffs/landings, pushing up and down on the bike, etc etc)

HSC is that damping trailing off as shaft speeds get higher (hitting impacts, rocks, bumps, square edged hits etc)... so essentially a blowoff curve. Not to nothing, and not all at once - just a curve of the damping regressing.

As vitox pointed out, the marzocchi adjusters don't really stay true to these conventions. The claimed LSC adjuster is pretty well an overall compression adjuster that controls damping over the entire stroke and any speed range, while the claimed HSC adjuster just adds end stroke compression damping (I wouldn't say it's HS specific really).

My advice would be to back the HSC (top) adjuster all the way, and use some light oil in there if needed to make sure it's doing nothing.

Then use the LSC (bottom) adjuster to control your fork's attitude, while not going far enough to affect traction when the shaft speeds get higher. Also make sure you are getting plenty of sag for your weight, and feel free to drop the oil heights until you are regularly using all or most of your travel, a lot of marzocchi owners wind up using only 80% of the travel because they set them up too progressively. You can go down to 190ml per leg safely if I remember correctly, at least down to 195 anyway.

Hope some of that quick messy info helps!

 

[RMR]

Udi,

Thanks, that's perfect.

I've never tried to set up a fork that didn't have distinct separation of LSC and HSC - well, I've been running the fork all season, I just haven't approached it very scientifically! This system of one main damping adjustment plus a bottom-out progression adjuster will require some rethinking. I'd also been wondering about oil height limits, so that's good to know, too.

I'm 160 lbs (plus gear) and I'm light on the bike, so I switched to Soft springs and it's been a world of difference. The feel of the front now matches that of the rear (Sunday, 300 lb/in spring) and I'm controlling the ride with spring and damping, rather than just spring, as was the case with the Regular springs.

There's another issue that's been on my mind, if anyone wants to tackle this, too (hopefully I'm not going over things that have been covered before).

I'm trying to improve the high-speed compression damping, since it's not as smooth as I'd like on braking bumps. For example, Whistler was rougher than usual when I was there and I developed bruising on the tops of my forearms from the shaking. Ouch.

Now, I could get similar damping characteristics by using thin oil and cranking up the damping adjustments or thick oil and backing off the adjustments. It may affect the degree of separation between HSC and LSC, but my main concern is how it affects HSC, since I suspect braking bump performance depends strongly on how wide open the HSC can get. I've determined the problem isn't due to excessively slow rebound.

Does anyone have any thoughts on the differences between thin oil with increased damping adjustment vs. thick oil and backed off adjustment?

Thanks!

 

[Udi]

Unfortunately I don't think you're going to get a heap of difference between thick oil + less turns on adjuster or thin oil + more turns on adjuster for a given amount of damping. By all means try it, but I'd try other things first.

Number one is rebound - you mentioned it wasn't excessively slow, but if you are running a setup with a light springrate and more compression damping, the third piece of the puzzle is getting the rebound as fast as possible.

IMO, with the fork setup as you have it (soft springs), the correct amount of rebound should definitely be zero clicks on the rebound adjuster (ie. backed all the way off) with a relatively light oil used as well. Sound a little extreme? It's not really, the adjuster doesn't give you total control over rebound range so there is still some damping with the adjuster backed all the way off.

But basically - with soft springs, it's very easy for the fork to compress deep into its travel. Ample amounts of compression damping will control the fork and stop it from getting lively enough to buck you. So with the attitude control out of the way, you really want to set the rebound as fast as you can handle (don't change all at once - try backing off a click every run, or maybe a click or two each weekend to slowly accustom yourself to it) - so that the soft fork can recover as quickly as possible and not pack down over consecutive impacts (which will most definitely hurt hands).

As you might have gathered from that, you're kind of stuck with using light oil in the LSC/Rebound leg anyway - so I'd learn to tune it that way.

 

[big-ted]

If the spring is "progressive" or "rising-rate", it would require 300lb's for the first inch, then say 350lb's for the second inch.
A "regressive" or "falling-rate" spring is the exact opposite of a progressive spring.

Except there's no way you could possibly wind a coil spring to be regressive. This must be achieved by varying the leverage of the compressing mechanism on the spring itself.

 

[Whoops]

Except there's no way you could possibly wind a coil spring to be regressive. This must be achieved by varying the leverage of the compressing mechanism on the spring itself.

You could put the spring in upside-down!

Sorry.


Here's a question (for a 66rc2x, sorry about that) - in the Right leg there's a black preload spacer. Can this be removed to reduce the preload?

I"m asking because I've tried fiddling with the oil heights, and run no air preload but still can't bottom the forks even on the hardest of hits with all compression backed off.


edit - i guess what I'm asking is - is the free length of the spring long enough to take up the length of the spacer if I remove it.

 

[RMR]

Whoops,

Sounds similar to the problem I was having with my 888. I don't know if they springs can be run without spacers, but I can tell you this: Soft springs solved everything for me. I went from considering selling the fork to loving it.

 

[DHRracer]

Except there's no way you could possibly wind a coil spring to be regressive. This must be achieved by varying the leverage of the compressing mechanism on the spring itself.

Wrong!What is your knowledge of spring design and the dynamics that would cause a coiled compression spring to be progressive,linear or digressive?What goes into a spring design to give it a specific rate or load?Do these elements change during compression?

 

[big-ted]

Wrong!What is your knowledge of spring design and the dynamics that would cause a coiled compression spring to be progressive,linear or digressive?What goes into a spring design to give it a specific rate or load?Do these elements change during compression?

Wow. What is it with everyone having small man syndrome on here these days? Fine. Explain to me how one would manufacture a coil spring with a falling rate if you're so smart then.

 

[DHRracer]

Wow. What is it with everyone having small man syndrome on here these days? Fine. Explain to me how one would manufacture a coil spring with a falling rate if you're so smart then.

First explain why you think it can not be done.What are the factors that give a spring its rate?We will ignore material choice,say we are only going to work with Chrome Silicone.Not to be a d--- about it but there are allways people on hear that are making claims about things that do not allways have the correct info. for.Does it do anybody any good to make claims based on assumptions?What people need when they have these questions are facts not assumptions.

 

[big-ted]

First explain why you think it can not be done.What are the factors that give a spring its rate?We will ignore material choice,say we are only going to work with Chrome Silicone.Not to be a d--- about it but there are allways people on hear that are making claims about things that do not allways have the correct info. for.Does it do anybody any good to make claims based on assumptions?What people need when they have these questions are facts not assumptions.

Hmm, I'm unclear as to whether you're baiting me, and in fact know to the contrary, or are simply wanting to know on what information I base my conclusions, in which case a simple request would have sufficed. In any case, why does everyone have to be so aggressive on here? I don't mind explaining my reasoning, but there's a polite way to ask, and if you have industry knowledge to the contrary then you could simply set me straight.

Anyway: A spring obeys Hooke's law, F=-k(x)x, where the spring constant, k, is a function of displacement, x. In a linear spring, k is independent of x. In a progressive spring, k(x)<k(x+d) where d represents some small increase in displacement. However, as the displacement of a spring occurs throughout it's length, the greatest displacement will occur in the region of the spring where k(x) is a minimum. Therefore it makes no difference as to the orientation of the spring.

It is therefore clear that, in order to have a regressive spring, one needs to use a material or construction that actually causes a reduction in k for increasing x. As far as I am aware, the only way this can be achieved is by compressing a material beyond it's elastic limit, which is highly undesirable, for obvious reasons.

Now, in the event that you are baiting me, care to prove me wrong and feel better about yourself?

 

[RMR]

DHRacer,

As far as I can tell, the only way you're going to get a falling-rate spring is to use some unconventional material or to allow the metal to undergo plastic deformation, in which case it'll be a falling rate spring only once.

Any material that's typically used in springs in linear in its elastic region - or near enough thereto that we'd be splitting hairs to say otherwise.

Now, we all know it's possible to have an overall rate that's regressive by combining a regressive linkage with a linear (or even rising-rate) spring, but it seems we're talking about the actual springs here.

Now, unless there's somethink big-ted and I are overlooking, can we please keep this on topic or split it out to a separate thread in Tech Talk?

 

[norbar]

Isn't the discussion a bit pointless as a regresive spring shock would be bottoming out all the time? Who cares about it anyway.

And it started as such a good tread

 

[RMR]

Isn't the discussion a bit pointless as a regresive spring shock would be bottoming out all the time? Who cares about it anyway.

And it started as such a good tread

As I said, I hope an admin can split from #21 onward into Tech Talk. Thanks in advance!

 

[Udi]

Not to be a d--- about it

Hate to say it but you're doing a great job at that. I think that was also the only bit of legitimate information you posted. Seriously, butt out of the thread instead of starting (wrong) arguments about something pretty much irrelevant.

RMR - care to try/comment on the rebound thing? Or share your current settings. Hope you read my post.

 

[RMR]

Hate to say it but you're doing a great job at that. I think that was also the only bit of legitimate information you posted. Seriously, butt out of the thread instead of starting (wrong) arguments about something pretty much irrelevant.

RMR - care to try/comment on the rebound thing? Or share your current settings. Hope you read my post.

I read your post, but I have to disagree about the rebound. It's true that mine will be slower than that of someone who's using stiffer springs, but if I set it up with that strong of a bias toward braking bumps (i.e. very light rebound damping), then it's going to buck me around when I'm taking bigger hits.

The problem is that I have about the same unsprung mass as anyone else, yet my sprung mass (that would be me) and upper body strength are lower than those of most people here, so I'm stuck with worse braking bump performance relative to big hit performance or vice versa.

The ideal solution, of course, would be to reduce the unsprung mass in proportion to my lesser sprung mass, but that's both difficult and expensive. The one step I took was to put in a 250 g tube, cutting half a pound off the unsprung mass - not bad for five bucks!

 

[Udi]

Nope, that's where you're wrong. That's why I was hoping you might at least be willing to give my suggestion a try over a number of weeks (like I said - not all at once).

Sprung mass/unsprung mass isn't really a large consideration here (especially when it comes to the particular issue being discussed - rebound damping), and I think ultimately it's a lot easier to set your suspension up to suit yourself than whine that you lose out compared to the bigger tougher guys in braking bumps etc. For the record, I weigh less than you (~150lbs at most) and so have spent a lot of time tuning suspension to suit.

The reason bucking won't be an issue is because with ample compression damping, the fork isn't going to end up overly deep in the travel too often - ie. it won't use up an excess of travel to absorb a bump, therefore it won't buck you nearly as much on the rebound stroke. Now ample compression damping is something very few people run, that's why it might be hard to get your head around running faster rebound - because, without that LSC taking care of attitude control you DO need more rebound damping to stop the fork throwing you around.

But light springs coupled with moderate levels of LSC definitely call for faster rebound (otherwise the fork just WON'T be responding fast enough, and it's going to hurt - both you, and performance), and I think it will benefit you all round if you take a chance and try it over a few weeks. If you do it all at once you'll be disappointed, but a little bit at a time and you might notice things improving all round.

Just a relatively educated suggestion anyway. Ultimately it's up to you if you want to try it or not.

 

[RMR]

Udi,

I know this is an internet forum and all, but there's no need to take how-to-be-a-dick lessons from DHRracer and tell me I'm "whining" about being light when it was just a speculation as to one possible cause of the set-up difficulties. I'm just trying to think through this and come up with a way to improve washboard performance without compromising other aspects of the suspension's functioning.

If I'm willing to type this much over the issue, of course I'm going to experiment with your suggestions. I didn't waste all this time with the intention to change nothing. I may question your reasoning, but it's all in the interest of science and I'm aware that speculation is no substitute for experimentation. There's a difference between a discussion and an argument, but I guess this is the internet, where it seems the former has become obsolete.

With that out of the way, perhaps we can get back to discussing things without hostility.

The only situation in which my 888's performance seems off is braking bumps; everything else seems excellent, though I'm open to the possibility it could be better.

I see what you're getting at with increased LS damping. (Given what's been said about how 888 damping works, would it be more functionally accurate to call it something like "general damping" and "bottom out"?) Soft springs and light general damping permit the fork to get deep into its travel - quite frequently, at that. I can see how fast rebound would also help to keep the fork up. In that my greatest concern is with braking bump absorption, I’m not sure keeping the fork high in the travel is the top priority; it seems to doing well already. As I said, though, I’ll try it.

I'm not clear on how more general damping will help braking bump performance, especially if you feel certain that unsprung mass is a minor factor. I'm aware that faster rebound would help, though I'm concerned the force on impact would be similar (less force from the spring, but more force from damping) and the rate of rebound could actually be slower.

The idea of slower wheel rebound from less rebound damping sounds absurd, I know. First, I should explain that I rarely brake on washboard. Instead, I usually brake at the very end of the washboard or completely after it (whoever creates them really needs to try sticky tires!). As such, the fork is near the top of its travel over the washboard and perhaps there’s no reduction in rebound damping that will make up for less displacement of the spring, as could happen with increased compression damping.

To summarize, it seems unlikely to me that more general damping will improve performance over washboard, even with faster rebound. It’s possible this could improve the ride elsewhere, though I’m happy with how it performs everywhere other than on washboard. Obviously, I’ll try your suggestion, I’d just like to discuss the theory, too.

I may have to wait until next season to experiment with the fork, since downhill season is mostly over where I am right now, but don't you worry, I certainly will experiment.

 

[Udi]

Ah I wasn't having a go at you with the whining comment but seriously all I was saying was - you can't change your body, but you can change your suspension. And as I'm sure you already realise, bigger guys will have issues with accelerating/braking/changing direction as fast as lighter guys, as well as breaking more parts etc.. I think we've got it good if anything.

I wasn't saying more compression damping would help braking bump performance either, I guess I just assumed that you entered the thread asking about compression damping with the intent of running some/more.

More comp damping just means you can be more aggressive with the bike around corners (exit faster) and generally just gives a setup that can handle more aggressive use without wallowing all over the place... while still letting you use all your travel and keep your light springrate + sag. Setup right, you should be able to get away with making very little impact on traction and bump absorption as well... but not having a true LSC / HSC adjuster makes it difficult to reach an ideal relationship... that's something I guess I can't help you with.

Anyway, if you were never looking for those benefits - then yeah there's probably no point in winding up your compression damping. The only way it might help your hands over braking bumps is if you are riding too deep in the travel, and marzocchi's relatively progressive springrate (not due to springs, but the air volume reduction causing ramp-up) is resulting in that deep section of travel being harder. Other than that, there's probably no sense in running more. Sorry if I sidetracked your original question.

As a sidenote -
Regarding your first post, LS/HS aren't each a set of shims in the stack, the way it works is that LS is generally a port of fixed size, with a needle (or other) valve that changes the size of the port. The HS setup is in parallel to this, and as oil speed increases enough that the damping spikes (when the oil tries to go through the LS port too fast), the HS setup (a variable aperture valve - shim stack or sprung valve) opens up to allow more oil to flow through the damper and therefore let the amount of damping regress.

Without opening up the RC2 cartridge I couldn't say exactly what the damper does, and unfortunately they are sealed shut so any disassembly would be destructive.

 

[Udi]

Oh, and as a little food for thought - I guess you've got to decide at some stage if what you want to do is feel comfortable or go fast. Obviously if your hands feel like they're about to fall off halfway down the run, it's going to slow you down and cause issues - but if it's not that bad then I'd suggest doing hand/arm exercises to strengthen them, even just doing runs will build them up over time... and in general just dealing with it. Then you can set your suspension up in the way that'll get you the fastest times

Just that right now to me it sounds like you already have a real soft setup - 888RC2X with soft springs for a 160lb rider is plenty soft, and if you aren't running much compression damping (and your rebound isn't too slow) then you've pretty well got a fork that should be very comfortable to ride on. Apart from backing off the top compression adjuster, and running the oil height so you can use say 95% of the travel regularly... I couldn't really suggest anything that made your fork feel nicer, so I'd really suggest the problem is elsewhere.

Not patronizing - but honestly, it could be your grips, it could be that you're gripping the bars too hard, and as above it could just be that your hands/arms are weak... but I doubt the fork is the culprit.

 

[RMR]

I think the advantage is with the big guys, simply because most of the really, really fast guys are big. That's academic, though, since, as you said, we are what we are. Also, I ride a lot of cross-country and road, which is where being light really helps.

The problems that braking bumps are causing me is more of a comfort issue than a performance issue, that's true. It's not so much my hands as the tops of my forearms. When I ride, it's usually non-stop runs all day; I put in more than twice as many runs as most of my friends, just because that's how I have the most fun. I get bruising on the tops of my forearms after a few consecutive days of that. Compression wraps help, but it's still very uncomfortable.

Yes, I do run that fork really, really soft, with a bias toward comfort. It might be faster to run it firmer, but I'd hate to have to ride like normal people - you know, taking breaks and all. I'll see if I can find a compromise, especially when I'm not going for a marathon session.

As we've now clarified, my question was quite specific, not just a general one of how to use compression damping. I'm quite familiar with that. It's been very helpful to have clarification of the exact functions of the two compression adjusters and I appreciate the discussion of ideal set-up.

Regarding the mechanical systems involved, I probably extrapolated too far. My knowledge of shimmed dampers is mostly based on a couple that I got to inspect in detail. As I recall - and it's been ages - both the LS and HS were shimmed to give a smooth transition between the two damping modes.

 

[ArthurDH]

i too found that making my fork firmer by adding more compression damping helps me a lot on very very VERY gnarly tracks