[thaflyinfatman]

Alright, so sorry for being a little slow.

In dumb people terms, what does the floodgate do? Adjust how much force it takes to go to the HSC circuit as well as adjusting the HSC at the same time?

Sorry...

Essentially, yep.

To re-iterate the spring preload analogy: it takes a certain amount of force to overcome preload on a spring, and therefore to reach any point in the spring's travel, you will need the spring displacement force (eg for a 400lbs/in spring, to compress it one inch, you'd need a force of 400lbs) plus whatever the preload force is (say you'd preloaded it half an inch, that'd be an extra 200lbs, so a total of 600lbs to move it half an inch into the travel).

 

[Cave Dweller]

Yeah except for the whole damper-before-the-shim-stack thing...

The shims are needed to disapate some of the energy in high speed hits (ie slow the fluid down). I hope your not trying to say a ported damper is better then a shimmed damper at controling oil velocity, cause you know that aint so.....

Once the 3 holes down the bottom are fully open they don't do squat im fairly sure, those holes are very large, oil will flow unrestricted.

Esentially, one is good at low speed, the other is good at high speed, both have differant damping curves. You adjust at which point they change over.

 

[thaflyinfatman]

The shims are needed to disapate some of the energy in high speed hits (ie slow the fluid down). I hope your not trying to say a ported damper is better then a shimmed damper at controling oil velocity, cause you know that aint so.....

Once the 3 holes down the bottom are fully open they don't do squat im fairly sure, those holes are very large, oil will flow unrestricted.

Esentially, one is good at low speed, the other is good at high speed, both have differant damping curves. You adjust at which point they change over.

Sorry but you clearly don't understand just how the MC thing works, or why shimmed dampers are generally superior to constant aperture (ported) dampers. First of all, the effective porting of the MC damper is NOT constant, that's exactly what the compressible MCU tube allows for. It opens up a gap between the PLATE AND THE PISTON. That gap is not going to be huge, it's only going to be as big as is necessary to prevent the oil pressure spiking, and the oil getting between the piston and the plate is going to have a significant friction effect. This is EXACTLY WHAT SHIMMED DAMPERS DO - the shims move away (although they bend from the centre out rather than moving linearly away so you can tune it more easily, but the general effect is the same) from ports sufficiently large enough that the ports themselves do not have a significant damping effect, and the primary source of the friction is the gap between the shims and the piston (piston including edges of the ports; basically whatever gap is the smallest one the oil has to flow through). Shims themselves don't "dissipate energy", the shear friction of fluid flowing through a small gap - REGARDLESS of what materials that small gap is between - is what converts the kinetic energy into thermal energy.

Please get over the whole "omg shims" thing, because ANY variable aperture damper is inherently capable of performing the same tasks. Shims are used due to their ease of tuning with regards to non-linear deflection (whereas a spring is typically fairly linear), but RS has the floodgate thing to get around that anyway.

Hence, shim stack is still redundant.

 

[peachy]

sounding like, effectively, there are 2 "Shims" in the booxers.

 

[davep]

FFM
I understand your descriptions and agree! But without running a dyno on each damper seperately, I do not think that you can say for sure that they are truely redundant. They do accomplish the same thing, and work in the same way, but the two dampers might have very different damping rate curves. There are all kinds of different shim stack geometries that can be used, to change how the shims deflect.

The other thing that I think might cause a difference, is the seperate holes in the LSC/gate set up. When the sleeve is pushed up, it opens one hole and then another. The effect, it would seem, is that the 'port' is variable but the variation is not continuous.

Certainly these two different dampers could be tuned to perform very similarly, but it seems just as possible, that they could be tuned quite different.
The TPC+ used two shimmed dampers that, at the near-end of travel, worked in series. Certainly a different application, but it worked and it worded well.

Just thinking outloud.................................

 

[big-ted]

Just thinking outloud.................................

Just folowing suit, some good stuff here guys...

So, at the moment, I am unhappy with my Team for two reasons (aside from the leaking oil from the scratched stanchion):

1) seems to bottom to easily,
2)feels like it's spiking on real high-speed hits. The washboard type vibrations you get at places like Whistler.

I was considering running lighter oil in the MoCo to alleviate this, but it sounds as though I could run into problems with the fork bottoming, due to the (fixed) valving of the BB speedstack no longer being sufficient to dissipate the energy of a large hit. How about if I raised the oil level as well to reuce the volume of the upper air chamber? I think a more progressive fork would be a good thing also. I run my damping controls nearly fully open, so I can increase these if needs be. The MoCo comes stock with 5wt oil. 2.5wt seems mighty thin...

 

[julian_dh]

im kinda unhappy with my fork too, not in the damping sense but it seems to have a ton of stiction compared to alot of other forks ive tried even though i tri flow the dust and oil seals regularly and have rebuilt and changed the oil.

recently i tried pushing my damper all the way down when installing to get as much negative pressure in that leg as possible. the fork hugs the ground better, and dosen't spike on stutter bumps as it used to but, the stiction is still there.

also the last time i changed my oil i used the measurement on the side of the bottle the clear strip and turned out it was waaaaay off i was running about 25-50ml of oil i only realized this once i turned it to full compression and it didnt lock out it actually blew off, where as before it was hard as a rock and couldn't go past an inch of travel.

 

[vitox]

julian thats a bit weird have you tried cycling it one leg at a time when removed from the crowns to see if the structure is ok?

 

[Cave Dweller]

Like Davep has said, i think its a big call to just say it does nothing.

You really think RS are going to spend extra money putting it in if it does nothing? They could leave it out, sell it for the same price and make more profit.

Dampers (and springs for that matter) can be either in series or parallel, it does not matter, as long as they are designed correctly for the application.

For example avalanche rear shocks. Have you ever noticed that on a rebound plunger it has shims on both sides (for rebound and compression)? Then you have a needle and blow off valve in-between the shock body and reservoir IN SERIES with the other compression shims. Maybe you should ring craig and give him some advice that the compression shims on the rebound rod are useless as they are in series with the needle/blow off valve. Im sure he would laugh at you.

Or maybe the new cane creek double barrel. OMG!!! Shim stack and blow off vales/needles in series, infact the rebound rod compression shims are in series with 2 sets of needles and blow off valves. Better give ohlins a call and tell them their 30 years of experience in building the best shocks around is wrong.

 

[Udi]

It's nice to see this thread has exploded into a debate on whether dampers in series are appropriate or not, I only asked how to dissasemble the speedstack... but I knew this would happen when I posted, so it's all good.

Cave Dweller -
The team/wc are nicer than the race in the sense that you can control the floodgate, as TFFM pointed out. I'll restate some stuff I already have, to cover why I feel the stack is working against the rest of the damper. By redundant I don't mean it does nothing, but that it is doing nothing good.

On the race, the LSC won't blowoff until some predefined blowoff(floodgate) level which is too late, and tends to induce spiking when cranked. On the team/wc, you can get away with more LSC before spiking occures on high speed impacts. BUT, because there is still a secondary compression stack, after the LSC has blown off, i'm led to believe that it is still providing compression resistance on these fast impacts (think braking bumps) and therefore the fork is not reacting enough nor reacting fast enough. In my eyes not only is the HSC stack a little redundant, but it is also working against the advantage the floodgate gives the team and worldcup. For the record, my other fork is a pike air, so I know how the motion control damper feels with the floodgate, and without the speedstack.

You don't seem to understand that we (or at least I) don't want any extra compression damping after the blowoff stage, and it is for these faster impacts that I want my 203mm of travel to be actively used, until I smash into the next corner (or crank down on the pedals angrily) engaging the LSC circuit again. Maybe for bigger/heavier riders some high speed compression could be beneficial (though, i'd like to see why), but for me (from what I have felt on-track) less would be preferable.

 

[julian_dh]

julian thats a bit weird have you tried cycling it one leg at a time when removed from the crowns to see if the structure is ok?

yep i just rebuilt the fork the other night and checked everything. besides my maxle giving me a hard as hell time it seems to be fine.
its just wierd because ive tried a couple other forks race, team and world cup, and some of them were butter like a tripple 8 in the first inch of travel being very lose feeling.

im not sure whats going on but the negative pressure in the moco leg really helped the fork dosen't spike on slap landings and stutter bumps anymore but theres still a bit of stiction.

im sure its not the dust seal because i popped them up and cycled the fork and it was still there. and its only in the first bit of travel im leaning towards it being the orings on the damper shafts, oil seals or bushings.

 

[julian_dh]

You don't seem to understand that we (or at least I) don't want any extra compression damping after the blowoff stage, and it is for these faster impacts that I want my 203mm of travel to be actively used, until I smash into the next corner (or crank down on the pedals angrily) engaging the LSC circuit again. Maybe for bigger/heavier riders some high speed compression could be beneficial (though, i'd like to see why), but for me (from what I have felt on-track) less would be preferable.

dose you fork spike when you slap it down on the ground?
even with a 25lb/in spring the fork would spike if i slapp the front end down which felt really harsh on stutter bumps roots ect. when i rebuilt the fork i pushed the damper almost to bottom out before the shaft and foot nuts were righten'd and the fork now dosen't spike has alot less bottom out and it much smoother hugging the ground.

also this isnt an isolated case with boxxers i rode a friends shiver as a back up fork that was in a garage for 4-5 years and even with the stock springs it was the worst feeling fork ever so i decided to crack it open and ssssssssstttttt an assload of air came out and the fork felt amazing afterwords.

just my 2cents

 

[davep]

yep i just rebuilt the fork the other night and checked everything. besides my maxle giving me a hard as hell time it seems to be fine.
its just wierd because ive tried a couple other forks race, team and world cup, and some of them were butter like a tripple 8 in the first inch of travel being very lose feeling.

im not sure whats going on but the negative pressure in the moco leg really helped the fork dosen't spike on slap landings and stutter bumps anymore but theres still a bit of stiction.
im sure its not the dust seal because i popped them up and cycled the fork and it was still there. and its only in the first bit of travel im leaning towards it being the orings on the damper shafts, oil seals or bushings.

It should be fairly easy to figure out the issue with a little systematic examination. First and foremost, make sure that the fork is not twisted in the stantions. Loosen all the top crown bolts, including the one on the steer tube, and cycle the fork and then re-tighten. Also you said that you axle is giving you a hard time. If it does not line up with the holes in the lowers, that is a good sign that the fork is bent.

If all that checks out, Pull the fork out of the crowns (leave the crowns on the bike) and cycle the damper side by hand and feel for stiction. Air down the spring side so it has just enough air to keep it extended. Cycle that side by hand feeling for stiction. Whatever side is giving the stiction, gut it, and re-insert the stantion w/o inner parts. Is the stiction still there?? If no, the internals are the cause, if yes, the stantion interface is at fault. BTW there is a seal below the dust wiper that you removed(according to the manual), You should be greasing this area (between the two seals).

I am a little confused that you say that you just rebuilt the fork, but you dont know if the o-rings or seals are dry and/or causing stiction. You should have been able to find the cause when you took the fork apart. Did you just change the bushing oil?

Before you pull it apart again, get yourself a graduated cylinder to measure oil ($4 at the moto store) and some slick honey-type (thin, non-lithium based) grease. Whe you re-assemble, ALL seals and o-rings need a thin coat of grease. In addition, you should pack grease just under the dust/oil/seal/wiper.

 

[peachy]

i'm not sure if this will help but i just pulled my WC off yesterday to replace an oil seal and my air side has very little stiction but the MoCo side has more... is that normal? i don't know really but i'm assumming yes due to the fluid that's moving in/out the damper.

 

[thaflyinfatman]

FFM
I understand your descriptions and agree! But without running a dyno on each damper seperately, I do not think that you can say for sure that they are truely redundant. They do accomplish the same thing, and work in the same way, but the two dampers might have very different damping rate curves. There are all kinds of different shim stack geometries that can be used, to change how the shims deflect.

The other thing that I think might cause a difference, is the seperate holes in the LSC/gate set up. When the sleeve is pushed up, it opens one hole and then another. The effect, it would seem, is that the 'port' is variable but the variation is not continuous.

Certainly these two different dampers could be tuned to perform very similarly, but it seems just as possible, that they could be tuned quite different.
The TPC+ used two shimmed dampers that, at the near-end of travel, worked in series. Certainly a different application, but it worked and it worded well.

Just thinking outloud.................................

Yeah, the damper curves may well be different, but from a conceptual standpoint, it IS redundant - IMO they should have just tuned the primary damper to have the characteristics it needed. Because having a second damper in series means that you need a second LS port (before the shim stack opens to allow flow) to create the hydraulic pressure spike necessary to open the shims.

The port variation IS continuous when you think about it, because the distance between the plate and the PISTON (not the size of the ports themselves) is never going to exceed the size of the ports (unless you can somehow manage to get a hit so hard that the inertia of the ~20 gram piston itself keeps compressing the plastic tube), so it will be the limiting factor. That distance DOES vary continuously from zero to whatever.

 

[thaflyinfatman]

Like Davep has said, i think its a big call to just say it does nothing.

You really think RS are going to spend extra money putting it in if it does nothing? They could leave it out, sell it for the same price and make more profit.

Dampers (and springs for that matter) can be either in series or parallel, it does not matter, as long as they are designed correctly for the application.

For example avalanche rear shocks. Have you ever noticed that on a rebound plunger it has shims on both sides (for rebound and compression)? Then you have a needle and blow off valve in-between the shock body and reservoir IN SERIES with the other compression shims. Maybe you should ring craig and give him some advice that the compression shims on the rebound rod are useless as they are in series with the needle/blow off valve. Im sure he would laugh at you.

Or maybe the new cane creek double barrel. OMG!!! Shim stack and blow off vales/needles in series, infact the rebound rod compression shims are in series with 2 sets of needles and blow off valves. Better give ohlins a call and tell them their 30 years of experience in building the best shocks around is wrong.

I'm not saying it DOES nothing, I'm saying it's redundant, and realistically a superfluous way of compensating for a (hypothetical) problem which by rights could and should have been solved with the original damper IMO (if there is actually a problem at all, and comparing my Race damper with the Teams/WCs I've tried, I've noticed SFA difference). Would RS really put it in if it did nothing? Could have sworn you used to be one of the RS-is-full-of-it-and-they-survive-on-marketing crew, although I could have simply mixed you and the whole only-enough-knowledge-to-be-dangerous thing up with another prominent anti-RS stalwart.

Have you noticed that rear shocks need a huge amount more damping than forks (within a confined space too)? Have you noticed that they don't have a second oil-flow piston like Motion Control and TPC (and Avalanche forks I believe, probably even Fox too) do? Have you noticed that the common bleed adjuster (aka rebound adjuster) also affects compression (as it closes the low speed flow in both directions) and thus needs a separate compression assembly elsewhere AS WELL (unless you can somehow create a 2nd, eccentric LS port and access it from somewhere other than the rebound piston)? Are you aware that the Cane Creek (yes OMG OHLINS) runs a full-piston-diameter oil displacement, and that the shims on the piston are for the purpose of damage prevention (they only open for cases of extremely high shaft velocity - note that there are no rebound shims on the CC shock) rather than as part of the normal compression circuit? Are you aware that this means that with the exception of hits that might otherwise cause damage to the shock, that there are no dampers in series here? Are you aware that on Ohlins' own shocks, they don't even have the shims on the piston, and that this is WHY they can create computer software (I know because I HAVE it) that can accurately predict the damper curve based on the clicker settings you input?

I'm not making these comments just to slander RS you realise - I own and am very happy with my Boxxers. I just disagree with the way they've done certain things in what is otherwise a very good fork.

 

[Udi]

I just thought i'd take the opportunity to point out that while I now own two motion control forks, I still kept my membership card for the RS-is-full-of-it-and-they-survive-on-marketing crew. Actually my card covers the entire SRAM lineup.

But this time round they made a pretty cool damper. I think the moral here though is, that just because it's there (re: speedstack) - doesn't mean it's good or the way it should be ideally.

Just to clear up some stuff - I did let the air out of my lowers (pushed down all the way with footnuts off) when I first got the fork. Also running a lighter fluid than stock - Silkolene Pro RSF 2.5wt. For the tech heads, it's a 13.60cSt / 465VI fluid. Stock oil is 16.10cSt.

Next ride i'll try one click less on the LSC than I was when I made it spike (to be fair I was running 5-6 of 7 clicks when I did that) and report back. However i'd still like to get in the stack and remove a few shims sometime. I think TFFM has covered the "why".

 

[Cave Dweller]

I'm not saying it DOES nothing, I'm saying it's redundant

??

It either does something or it does nothing. You also need to remember that its possible the stock shims are not right for your style of riding and they may need to be changed.

Could have sworn you used to be one of the RS-is-full-of-it-and-they-survive-on-marketing crew, although I could have simply mixed you and the whole only-enough-knowledge-to-be-dangerous thing up with another prominent anti-RS stalwart.

Never said anything about RS and marketing, not sure where you pulled that from.

I never used to like the old RS stuff but have always been a big fan of TPC+ , in a lot of ways motion control is very similar.

Are you aware that the Cane Creek (yes OMG OHLINS) runs a full-piston-diameter oil displacement, and that the shims on the piston are for the purpose of damage prevention (they only open for cases of extremely high shaft velocity - note that there are no rebound shims on the CC shock) rather than as part of the normal compression circuit? Are you aware that this means that with the exception of hits that might otherwise cause damage to the shock, that there are no dampers in series here?

Ahhh…… actually they are on the rebound and compression side, better look again at the schematic.

“For high speed shaft movement, when the wheel hits a significant obstacle, the high speed damping takes over. This high speed damping is controlled using two components: the main piston shim stack and the high speed adjustment poppet valves. During an impact, the oil pressure builds up in front of the piston as the low speed passages are too small to handle the flow. The oil pushes open the poppet valve and piston shim stack allowing the suspension to move while absorbing the energy from the impact. The order in which these two high speed valves open depends on the settings. The piston shim stack is fairly stiff and will typically open later than the softer, high speed poppet valve. If the poppet damping is increased it may open slightly later than the main shim stack. Either way, this dual path valving enables the greatest control of damping characteristics for the high speed range for both compression and rebound strokes”

Hmmm...... sounds familiar.

Anyway, the whole point of the discussion is that i don't think the black box stack is redundant. If you think it is, pull it out and tell us how you went, i would be interested to hear.

Are you aware that on Ohlins' own shocks, they don't even have the shims on the piston, and that this is WHY they can create computer software (I know because I HAVE it) that can accurately predict the damper curve based on the clicker settings you input?

What are you talking about? All the ohlins MX stuff I have seen uses shims on the pistons. Which model shocks are you referring to, road bikes?

And that software comment doesn’t prove anything. It just means that modelling shims is a lot harder then a simple orifice. I know, i have developed non-linear matlab simulation code before, not easy by any stretch of the imagination.

 

[thaflyinfatman]

??

It either does something or it does nothing. You also need to remember that its possible the stock shims are not right for your style of riding and they may need to be changed.

It does something (I have never said otherwise), but that doesn't make it any less redundant, since you already HAVE a HSC damper as I explained above. In order to have the secondary shim stack, you basically have three options as to how you force oil through it:
1. Have ANOTHER lsc port in parallel with the shim stack, to cause hydraulic lock/pressure spiking in order to open the shim stack. This is obviously going to affect your primary LSC circuit too.
2. Have no secondary LSC port, and just run ALL the oil through the shims. Sort of defeats the point of the first damper at that point, you might as well have just had a shim stack and needle valve.
3. Have something that closes off a secondary LSC port once the primary damper/LSC thing "blows off". This would have to be based on the displacement of the plastic compression tube/primary piston, but since it's apparently rigidly joined to the secondary shimmed piston (and the amount of displacement required to blow off is variable anyway), I very very much doubt this is the case.

I never used to like the old RS stuff but have always been a big fan of TPC+ , in a lot of ways motion control is very similar.

Yeah I'll agree there - MC is IMO just a way of getting around the TPC patents. On the whole, I think it's a very good system.

Ahhh…… actually they are on the rebound and compression side, better look again at the schematic.

“For high speed shaft movement, when the wheel hits a significant obstacle, the high speed damping takes over. This high speed damping is controlled using two components: the main piston shim stack and the high speed adjustment poppet valves. During an impact, the oil pressure builds up in front of the piston as the low speed passages are too small to handle the flow. The oil pushes open the poppet valve and piston shim stack allowing the suspension to move while absorbing the energy from the impact. The order in which these two high speed valves open depends on the settings. The piston shim stack is fairly stiff and will typically open later than the softer, high speed poppet valve. If the poppet damping is increased it may open slightly later than the main shim stack. Either way, this dual path valving enables the greatest control of damping characteristics for the high speed range for both compression and rebound strokes”

Hmmm...... sounds familiar.

Anyway, the whole point of the discussion is that i don't think the black box stack is redundant. If you think it is, pull it out and tell us how you went, i would be interested to hear.



What are you talking about? All the ohlins MX stuff I have seen uses shims on the pistons. Which model shocks are you referring to, road bikes?

And that software comment doesn’t prove anything. It just means that modelling shims is a lot harder then a simple orifice. I know, i have developed non-linear matlab simulation code before, not easy by any stretch of the imagination.

I stand corrected - very partially. From http://www.canecreek.com/fileadmin/canecreek/products/shocks/Decline_Aug_2005.pdf
Under "The design", I quote:
"The main piston of the DB is heavily shimmed and will only open to compensate for hard impacts. Since this design forces a lot (nearly all) of the oil through the circuit, it creates an extremely wide range of adjustment. In Ohlins' original design that is used in many high end auto and motorbike racing, the piston is solid so that it pushes all of the oil through the circuits. Noting that shaft speeds are significantly higher for mountain bike shocks than auto racing, Cane Creek decided to use a shim stack design on the main piston for performance and safety reasons."
In other words, preventing spiking at the highest shaft speeds, and potential resultant damage to the shock.

Here is the Ohlins stuff it's based on: http://www.ohlins.com/Automotive/InsideTTXContainerPage/TTXHowitworks/tabid/133/Default.aspx
Note no shimmed main piston.

Uhh actually the software comment proves the EXACT OPPOSITE in this case. What it shows is that the consistency and ease of predictability of the single degree of freedom (no need for extremely complex simultaneous/iterative calculations regarding pressure drop) of their positive displacement/constant pressure drop, single damper system, can be easily and accurately modeled in a simple program that they are willing to provide to the general public for free.

And if not for the fact that I have a Race damper as mentioned above (hey $75, can't complain!), I would pull the shim stack out and compare back to back.

 

[peachy]

somebody help Udi remove the speedstack so he can compare it with and without.

 

[Cave Dweller]

somebody help Udi remove the speedstack so he can compare it with and without.

I recon you can do it with a race, just need to modify the amount the LSC lifts off. Probably some preload spacers at the end of the rod would do it (not exactly sure how you would do it)

I don't think you could actually remove the stack without removing part of the gate system, probably best you could do would be to take off the shims so it doesn't do much.

thaflyinfatman. i don't think its worth arguing further as its going around in circles, and its all hypothetical until someone actually does it and says its better or worse for them, which would still be subjective anyway.

 

[thaflyinfatman]

That's a very roundabout way of eating your words.

 

[Cave Dweller]

That's a very roundabout way of eating your words.

No its not. Im saying its not worth arguing over the same hypotheticals for another x number of pages, i've made my points, you've made yours.

I still think it performs a useful function, you think it doesn't, its not worth my time to keep arguing so im letting it die, i have a PhD to finish *grumble grumble* Neither can be proved right until someone actually pulls the stack out, and even then it would be subjective. For instance if udi did it, he is small and a feather weight, probably around 65kg tops, im 95kg and a good 1 to 1 1/2 feet taller then him, he might find it better without the stack, or with it shimmed more lightly (which is probably what his problem is). Doesn't mean it would be so for me. Everybody likes their suspension set up a certain way otherwise forks wouldn't come with the adjusters.

 

[thaflyinfatman]

Hey you were pretty keen to argue when you were so sure that everyone did things the way you described, then all of a sudden you're too busy? hahaha, oh, and you're not 1 to 1.5 feet taller than Udi unless you're a minimum of 6'9". I'm actually heavier than you (100kg and just under 6'3") and I still don't find any advantage to the Teams over the Races, except for the Floodgate.

Why are you neglecting your oft-mentioned-yet-irrelevant-to-the-topic PhD to sit on interwebbe forums and tell me that you should be off doing said PhD?

 

[Cave Dweller]

Hey you were pretty keen to argue when you were so sure that everyone did things the way you described, then all of a sudden you're too busy? hahaha, oh, and you're not 1 to 1.5 feet taller than Udi unless you're a minimum of 6'9". I'm actually heavier than you (100kg and just under 6'3") and I still don't find any advantage to the Teams over the Races, except for the Floodgate.

Yes, i am too busy to keep arguing the same thing over and over again, i don't agree with everything you say so why keep pushing the point? I spend enough time procrastinating as it is. And who, besides yourself, said your totally right about what you said?

And have you meet udi have you? Maybe 1.5 foot was a stretch, probably closer to 1 foot, but he is a small guy and a fair bit lighter then me, and im fairly sure he has his supension set up differant to me as well. I'll let you know this weekend after i've ridden with him.

 

[J5ive]

Maybe a long shot. But has anyone called or emailed rockshox to ask how to tune this shim setup?

 

[Udi]

CD - done a buller trip with TFFM and he's been to bris also.
10 points to guess who he is, if you haven't already figured it out. And i'm 5'10.... maybe a foot is a little optimistic?

J5ive - don't you know anything? it's way more fun arguing over the intarnet!

 

[Cave Dweller]

CD - done a buller trip with TFFM and he's been to bris also.
10 points to guess who he is, if you haven't already figured it out. And i'm 5'10.... maybe a foot is a little optimistic?

Ding Ding, the penny drops

Argumentative bastered who won't let it go, 100kg and 6"3, im thinking its our good friend socket from farkin. Go figure....

5'10? Im bringing the tape measure. I could have sworn there was at least a head in it.

 

[thaflyinfatman]

Nah, Udi seems small because he's skinny. He's of pretty average height.

Come to Thredbo for the nats round, we'll sort this out mono e mono... that's right, a wheelie competition

 

[Cave Dweller]

Nah, Udi seems small because he's skinny. He's of pretty average height.

Come to Thredbo for the nats round, we'll sort this out mono e mono... that's right, a wheelie competition

Well, i can't wheelie more then 1 meter, so i suggest a beer drinking comp instead

I know i said i wouldn't continue this, but i was thinking about it last night and its bugging me.

Your example of the ohlins shock is for automotive and street racing/riding, correct? The spectral densities of main roads/race tracks are in the order of 40x10e-6 m3/cycle, compared to an unpaved 4wd track which is 100,000x10e-6 m3/cycle, a rough mtb track could be expected to be several orders of magnitude greater again due to large rocks etc. What does this mean? It means that for the same wavelength there is a corresponding increase in amplitude displacement, velocity and acceleration when traversed at the same speed. Basically, the energy input into the system increases.

You acknowledge that the CCDB has the piston/shim stack vs the flat solid disc of the automotive shocks due to the increased velocity having the potential to hydraulically lock the standard ohlins shock seeing its an orifice valve setup. But as described by CC it also allows for a fine tuning of the ride. That basically says that simple orrifice valves are no good at high speed hits and that a combination of both is required for high velocity applications.

I went through the ohlins stuff last night, I couldn’t find any motor cross (not road, touring or superbikes, they are not the same, MX is the closest to DH in terms of roghness) suspension that didn’t use a shimmed piston over a simple orifice

Im sure it has occurred to you that a rear shock piston travels 3 inchs vs a forks 8inchs. The internal velocity of the fork will be substantially higher then a rear shock.

So, wouldn't it stand to reason that the adjustable LSC ports of the boxxer, while able to control HSC to a point, were not specifically designed to perform that function? If you crank the gate down you will limit the the maximum orifice size causing hydraulic lock during high speed hits. I have felt his when i crank down the gate, my hands get very sore from the increased vibration.

If anything, is it possible to say that the gate is the redundant feature in the fork? We have seen that using a simple orifice valve at high speeds dont cut the mustered.

Realisitcally, i assume it is there to provide extra tunability and to allow for a fine tuning of HSC without having to go in and internally adjust the shim stack. Of course, if one finds the fork too hard damping wise even when the gate is backed all the way off then it may require retuning.

I actually think one issue with motion control is that it has no bypass on the black box stack to tune the HSC properly, which is something the mission control system addresses.

There you go, that should give you something to pull apart bit by bit and argue

 

[Udi]

I hate to jump in here - but have you read and understood everything he has already said? It usually takes explaining twice for me to understand anything he says; but without writing an essay,here are some points you need to consider.

- The MC damper is not a mere ported (fixed aperture) design as you say (you are at least suggesting it is inferior to a shimmed setup - and it is not!). The only performance benefit of a shimmed damper vs a ported damper is that the aperture is NOT fixed and can change depending on the speed of an impact. The MC damper achieves the exact same thing, as the impact increases, so does the gap between the two parts - giving more compression damping at medium speeds and less at higher speeds appropriately. Blowing off does not mean no compression damping, and it isn't a max damping to zero damping equation.

- Having a second shimstack is adding MORE high speed compression damping than the regular damper is providing, hence messing with the relationship of slower impact = more compression damping, and faster impact = less compression damping, with a smooth curve in between.

- The floodgate could be used to adjust the HSC pretty successfully (without the speedstack) - but turning it up overly is bound to increase harshness over fast bumps (which you are seeing) , because that's what excessive HSC does!

 

[Cave Dweller]

Yes, I read what he said.

But the total aperture size of the orifice is controlled by the linear stiffness of the MCU spring, X amount of force will open it Y, 2X will open it 2Y and the maximum amount it can open is controlled by the gate function (the gate limits the maximum amount it can open right, or am I wrong?). From my understanding this is a linear process, the damping coefficient is relatively constant, and as such easy to model as tffn notes. This doesn't mean it is good for high speed / rough applications as noted by ohlins/cane creek, it sounds like it is better suited to situations with not alot of variability, such a road racing.

A piston with shims is non-linear (most of the time, this is why the shims are set up in a pyramid fashion). The more pressure/force the more it will resist opening up the piston orifice by bending the shims, its very similar to leaf springs in a ute, highly non linear due to the effects of hysterisis and coulomb friction. A force X may open it Y, but a 2X force may only open it 1.5Y. From my understanding this is why it is better at controlling high speed oil flows, the damping coefficient changes according to fluid velocity. It is better suited to situations with a high range of velocities.

 

[thaflyinfatman]

Yes, I read what he said.

But the total aperture size of the orifice is controlled by the linear stiffness of the MCU spring, X amount of force will open it Y, 2X will open it 2Y and the maximum amount it can open is controlled by the gate function (the gate limits the maximum amount it can open right, or am I wrong?). From my understanding this is a linear process, the damping coefficient is relatively constant, and as such easy to model as tffn notes. This doesn't mean it is good for high speed / rough applications as noted by ohlins/cane creek, it sounds like it is better suited to situations with not alot of variability, such a road racing.

A piston with shims is non-linear (most of the time, this is why the shims are set up in a pyramid fashion). The more pressure/force the more it will resist opening up the piston orifice by bending the shims, its very similar to leaf springs in a ute, highly non linear due to the effects of hysterisis and coulomb friction. A force X may open it Y, but a 2X force may only open it 1.5Y. From my understanding this is why it is better at controlling high speed oil flows, the damping coefficient changes according to fluid velocity. It is better suited to situations with a high range of velocities.

Nah you've got that arse-backwards (I'm at uni atm so you'll get a longer reply tonight) - shimmed/variable aperture dampers are REGRESSIVELY non-linear (look at the damper curve for any of these), so that high speed damping doesn't become exponentially more than the LSC (which obviously fixed aperture dampers do, hence the spiking).

 

[Cave Dweller]

Nah you've got that arse-backwards (I'm at uni atm so you'll get a longer reply tonight) - shimmed/variable aperture dampers are REGRESSIVELY non-linear (look at the damper curve for any of these), so that high speed damping doesn't become exponentially more than the LSC (which obviously fixed aperture dampers do, hence the spiking).

Sorry, your right, I had it around back the front.

But the point I was trying to say is the relationship of the variable orifice with MCU spring is linear, a piston with shim is nonlinear, and your correct, the damping coefficient reduces to prevent hydraulic lock as evidenced by the gazillion damping curves in existence.

I still can't see how the adjustable aperture with a linear spring can provide the same sort of function over the extreme range of shaft velocities that a mtb will encounter.

The only way I could see it working is if that black plastic MCU spring is somehow non-linear, which I guess it could be (or could it, I know sfa about plastic), but even then the gate function effectively works as a bump stop doesn’t it, limiting the maximum size of the aperture?

 

[thaflyinfatman]

Yeah, without knowing the force/displacement curve for the MCU then it's hard to say. I'd be very surprised if it was linear though. More explanation to come later.

 

[LOOnatic]

And i thought i was a Boxxer nerd:biggrin:

 

[benno]

And i thought i was a Boxxer nerd:biggrin:

These guys aren't boxxer nerds, they're just nerds.

 

[thaflyinfatman]

You're right. One day we might even buy bikes and go riding down some slightly-inclined bike path somewhere.

 

[toodles]

uDi - maybe try running a 7.5wt or 10wt oil with your LSC turned down?

Tune your HSC circuit first with no LSC. You'll have to run as thick an oil as you can before you get too much HSC. Then close the LSC as needed.

Running with a thin oil means you need most of your LSC ports closed to get the feel you like. This ends up starving the the shimstack even once the speedgate shifts.

Downside to this is that - if like most people - you run your rebound all the way fast you might wind up ****ed.

 

[Udi]

Put the beers down boy, and get ready for coffs.