The end-all explanation to Motion Control Damping...- Mtbr.com
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  1. #1

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    The end-all explanation to Motion Control Damping...

    Ever wonder what the heck is with Motion Control? Why so many people like it? Why so many people don't like it (lack of setup)? Why is it just about the most versatile system you can use?




    Here's a breakdown of how motion control works:

    You have a plastic spring tube that compresses from the oil pressure. It can compress up to around a quarter inch.

    At the bottom of the spring tube is a hole. This is the compression hole. The compression knob turns a rod that adjusts how much of the hole is showing.

    The bottom of the plastic spring tube is sealed off from the inside of the tube to force oil through the compression hole. Locking the compression closes this hole.

    The bottom of the spring tube is a sleeve that covers the compression hole. As oil pressure rises the spring tube gets pushed back. The floodgate setting is nothing more than a metal rod that screws in and out and adjusts the distance from it and the bottom of the spring tube where the compression hole is. Under full open loose floodgate, the rod is all the way down and nearly touching the compression damper.

    When the compression is locked out, it will not open again until it has been pushed upwards by the oil pressure and is touching the floodgate rod. The floodgate rod opens the compression hole upon contact and opens it more and more depending on how high the oil pressure is.

    Backing the floodgate all the way up to full firm will cause the comrpression unit to travel a longer distance before being opened and letting oil through and leveling the oil pressure. The spring tube is something like 5000 lbs/in so moving it becomes very hard the longer it has to move before opening. This is why the fork can literally become totaly locked out with full FG. It's because the spring tube needs to compress more than the rider's weight can fullfill before openeing the compression hole.

    Quite frankly, it's the most effective and simple system you can make. The floodgate setting is pretty much like having an adjustable shim stack without having to change shims.




    Floodgate also works as a high speed valving:

    It requires over twice as much fork speed and pressure to get the compression unit to compress when it isn't fully closed. This is because the oil is allowed to flow through and doesn't create enough pressure and normal speeds to compress the spring tube enough to bring the compression unit in contact with the floodgate rod. Thus you must loosen the floodgate which lowers the floodgate rod closer to the compression unit. That way the floodgate rod is doing something on faster hits and is helping to level off oil pressures.

    In full open compression mode, the floodgate is useless no matter what setting it is in. There is just too much oil being let through the compression hole to generate enough pressure to push the spring tube back enough.

    You must close the compression hole half or all the way in order to effectively use floodgate as a high speed valving.

    Ideally you want to have the compression hole set fairly tight in order to control fork movement on slow speeds. Stuff like pedal bobing and fork dive are slow speed events. You want to close the compression so as to limit the fork's ability to move at slow speeds. You then want to loosen the floodgate so that the rod is all the way down to the compression damper. That way ANY movement faster than pedal bobing or fork dive will cause the compression unit to hit the floodgate rod and open the compression hole, thus letting oil through and letting the fork move like normal.

    The reason myself and Kapusta like that setting is because it provides the most consistant damping, very linear in respect to oil blowoff.

    Running the compression halfway open and closing floodgate all the way tight so the rod is way up will result in a super progressive damping, which is not what you want for most riding. It won't control ANY low speed movements and use too much travel at higher speeds. Running full floodgate with open compression is asking for a horrible ride no different than an SSV fork.

    Running full locked compression and using a light floodgate is the best you can get to a platform feel, but with better bump ability and consistant damping through the whole stroke. This setting doesn't degrade bump smoothness much and makes the fork ride higher and more controlled. IMO this system is incredibly more usefull and versatile than any SPV fork. I can't stand riding any SPV fork after having Motion Control.

    On the other hand though leaving compression full open is nice for maximizing wet traction, when traction is more important than eliminating fork dive or pedal bob.


    Well, there's the short explanation of it all...


    edit: one great thing about the Motion control damping system is that it provides a seamless movement when pushing open the compression hole with the floodgate rod. Instead of a system that has an on/off switch where it goes from locked to loose in 2 mm of fork compression, motion control has a bit of give before hitting the floodgate rod and letting oil through.

    The spring damper tube can compress roughly a quarter inch. Due to the fluid dynamics of the oil push rod, it takes more fork movement than 1mm to get the oil level to move up 1mm, thus there is a leverage ratio acting on the spring tube. This allows the fork to still compress even when the compression hole is still locked and hasn't hit the floodgate rod yet. Try locking compression and then running floodgate full tight, you will notice this compression in the spring tube adds up to around 20mm.

    That all provides for one hell of a seamless system.
    Last edited by Robot Chicken; 10-11-2005 at 07:32 AM.

  2. #2
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    Nice explanation. So maybe you can answer my question: Is there an advantage to external floodgate adjustments, or is internal good enough? Do you have 2 or more different fork settings that require different amounts of floodgate control?

    My idea is to have a fork that I can lock out for the road, use medium compression damping for smooth trails, and wide open for rough trails. How can you adjust a Reba to get those 3 settings?

  3. #3

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    Quote Originally Posted by LarryG
    Nice explanation. So maybe you can answer my question: Is there an advantage to external floodgate adjustments, or is internal good enough? Do you have 2 or more different fork settings that require different amounts of floodgate control?

    My idea is to have a fork that I can lock out for the road, use medium compression damping for smooth trails, and wide open for rough trails. How can you adjust a Reba to get those 3 settings?

    You would want a fork with external floodgate. The floodgate knob has indent clicks so making changes is fast and easy. Just count the number of clicks for each setting.

    You would end up most likely using the compression closed for roads and smooth trails. Add a little more floodgate for roads to get it more locked out. You can even completely lock out the fork if you wish, no give past 20mm, but still has 20mm to take road bumps. Run little to no floodgate on smooth trails.

    Rough trails feel good in either smooth trail setting or full open everything. It all depends on how much traction you're willing to give up in exchange for less brake dive and antibobbing.

  4. #4
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    Sounds right. Do you think the 2006 Rebas will be much of a change from the 2005?

  5. #5
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    Robo-C,

    It seems you've played a bit with your fork.

    How good is rebound damping?? Is it shims or drilled ports??

    I'm aware that MC Spring tube gives up some progressive damping that emulate shims thanks to the deflection on the tube. Then the fork hardly will spike.

    But what about rebound?? I've been eyeing forks and the new Toras and Recons look like a worthy options. The non-MC models have arguably the best value around... but those only have rebound adjustment. How good is it??

    I'm aware only difference between the Tora/Recon forks and the more epxensive brothers are that the FG setting is fixed (Kapusta already gave me a killer insight of pro/cons of fixed FG)... should the rebound damper is the same?

    Thanks for any info!
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  6. #6
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    I have only good things to say about the RS Tora 318 air model. The info on the motion control and floodgate settings was very interesting and helped me understand how the system works. While the Tora does have a fixed FG setting, the motion control and rebound adjustments work very well for a fork in this price range. The rebound adjustment is very responsive and offers a wide range of control, which is not the case in most forks in the price range.

    In my opinion the Tora offers the best performance by a long shot in this price range. The only question I have about this fork is its durability, and only time will tell on that since it is a new model for 06'

  7. #7
    "El Whatever"
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    Quote Originally Posted by Lumpy
    I have only good things to say about the RS Tora 318 air model. The info on the motion control and floodgate settings was very interesting and helped me understand how the system works. While the Tora does have a fixed FG setting, the motion control and rebound adjustments work very well for a fork in this price range. The rebound adjustment is very responsive and offers a wide range of control, which is not the case in most forks in the price range.

    In my opinion the Tora offers the best performance by a long shot in this price range. The only question I have about this fork is its durability, and only time will tell on that since it is a new model for 06'

    Thanks Lumpy!!

    I'll fight my wife for the money for one!!!

    Yeah... those Toras are priced as the MX Line from Zoke and their features blow away the Zokes. Let's see how do they hold up but so far no one is complaining the Rebas and Pikes from last year and the only difference between Toras and Reba/Pikes is the material of the sliders (steel Vs. Al) so they should hold up just fine.

    The Recon 351 has everything to be the budget fork of the year.... and the Tora 318 is a close second.
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  8. #8
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    In full open compression mode, the floodgate is useless no matter what setting it is in. There is just too much oil being let through the compression hole to generate enough pressure to push the spring tube back enough.

    You must close the compression hole half or all the way in order to effectively use floodgate as a high speed valving.


    How do you know that?


    Ideally you want to have the compression hole set fairly tight in order to control fork movement on slow speeds. Stuff like pedal bobing and fork dive are slow speed events. You want to close the compression so as to limit the fork's ability to move at slow speeds.

    Why so general? Yes, pedalling and braking cause low-speed action, but so do all types of bumps - and they are the reason why you have suspension at all. If you set the spring rate for maximum ride quality at slow speed, then you may want very little low-speed damping on top of that. Feeling a need for increased low-speed compression damping can be a sign of a too soft spring. And with such, you might get worse tracking and grip.


    You then want to loosen the floodgate so that the rod is all the way down to the compression damper. That way ANY movement faster than pedal bobing or fork dive will cause the compression unit to hit the floodgate rod and open the compression hole, thus letting oil through and letting the fork move like normal.

    That's another one-size-fits-all suggestion. If you have chosen a spring rate for maximum ride quality at slow speed riding, and then want the compression damper to increase stiffness at higher speed and prevent the fork from bottoming out hard at sharp hits, then you may want at least a semi-hard high-speed compression setting, especially if you are a heavy guy.


    The reason myself and Kapusta like that setting is because it provides the most consistant damping, very linear in respect to oil blowoff.

    Why do you think that setting would be more linear? Could it be that half-way settings are more linear, as exemplified in the pic below? The pic is not drawn to scale and proportion, and only illustrates a principle. I don't know the answer myself.


    Running the compression halfway open and closing floodgate all the way tight so the rod is way up will result in a super progressive damping, which is not what you want for most riding. It won't control ANY low speed movements and use too much travel at higher speeds.

    With half low-speed damping, you do have a restriction of low-speed movement. That's what the low-speed damper does. And you may not at all use too much travel at high speed, since the "low-speed" damper causes a very significant high-speed damping if it is not limited by a spring valve or shim stack.


    Running full floodgate with open compression is asking for a horrible ride no different than an SSV fork.

    SSV-like, yes maybe. Horrible, I don't know.


    Running full locked compression and using a light floodgate is the best you can get to a platform feel, but with better bump ability and consistant damping through the whole stroke. This setting doesn't degrade bump smoothness much and makes the fork ride higher and more controlled.

    Light low-speed damping, paired with a suitable spring rate for slow riding, and medium floodgate, might give better low-speed ride quality (=comfort, tracking, grip, speed) and better protection against over-travelling at sharp hits.


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  9. #9
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    Very nice explaination!

    Sounds much like motorcycle's Gold Valve Emulators for shocks and forks without shimmed dampers. Very effective.

    Externally adjustable low-speed and high-speed shimmed damping is more separatly tunable, and finely tunable by changing shims. But at a cost of more complex manufacturing and adjustable shimmed dampers are probably a bit heavier.

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  10. #10
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    I would kill to get my hands on a Fox 36Van to compair it's adjustabillity vs. my Pike Race. I'm sure that you can fine tune the 36Van a lot better having both high and low speed adjustments, but at the Pike's price range you simply cant beat how adjustable it is.

    For what its worth here is how I set my Pike up. This is on an 04 Kona Coiler with a 190 pound rider(with gear) and a FIRM spring. For trail riding, I set my FG 18 clicks from open and set the compression at full open. This gives me a very plush ride with very little bob. If I need to I can close the Compression knob to lock the fork for an out of saddle climb. When I am doing jumps or drops I leave the settings the same unless the drop is larger than 4 feet, then I will close the Compression half way(3 o'clock to 4 o'clock) and mabey add a few clicks of FG for a bigger drop(6-8 feet). Ive done drops up to 8 feet, and feel that this setting works very well. I have bottomed a few times, but mostly out of user error, and since I my last oil change, I havn't at all(I added an extra 5cc of oil, still with in Rock Shox oil height limits).

    I use my coiler for everything and couldn't be happier with my Pike. It's just so frickin adjustable and versitile......and the price is unreal! Best all-mountain fork on the market hands down, and it even does relitivly well at some light freeriding
    It's not a good ride if you don't scare yourself at least once.


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  11. #11
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    Sticky?

    I thought this old thread deserved a bump if not a sticky.

    I picked up a new 80mm SID Race (my 1st motion control fork) earlier this year for my old carbon hardtail and though I've been riding it, I didn't really get around to playing around with the settings all that much until recently, and this thread helped a lot in explaining how you can use the floodgate adjustment.

    I've never been a big fan of fork lockouts. I'd rather just tough it out climbing with the fork active rather than having to keep locking and unlocking it. But whenever i ride my rigid SS, I always get a smile on my face as a sprint up a climb, so . . .

    Well yesterday I tried the "full locked compression and using a light floodgate" suggestion from the OP and WOW! I was amazed, I was climbing like I was riding my rigid, but still able to use full travel when hitting a drop going down the other side, and all without having to manually lock or unlock my fork. Plus almost imperceptible brake dive. The responsiveness of the bike on the really tight twisty singletrack I ride was amazing.

    I'm not sure that I will always run this bike this way since it isn't quite as plush setup like this, but it was pretty cool and I will certainly play with it some more. Unfortunately yesterday was likely the last ride on that particular bike until next spring (I use one of my other bikes for winter riding).
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  12. #12
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    Quote Originally Posted by trailville
    I thought this old thread deserved a bump if not a sticky.
    .
    Just keep in mind that the plastic tube is not really a spring. I believe that misconception has been sorted out since this thread happened 4 years ago.

  13. #13
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    Quote Originally Posted by kapusta
    Just keep in mind that the plastic tube is not really a spring. I believe that misconception has been sorted out since this thread happened 4 years ago.
    But Rock Shox calles it a "spring tube" therefore it must be one. To be honest, I was never quite able to completely understand the spring tube concept anyway, and I did read a lot of those other threads. I think I need to physically see it.

    I just found this thread very useful in quickly explaining how to use the floodgate in combination with the compression settings. And I'm well aware that there is not concensus on even that aspect of motion control, but anyone that spends time on these forums knows there is not a single aspect of mountin bike design or riding that goes unargued, so it's far from surprising that something as complex as modern suspension damping would have differing opinions.

    Wouldn't it be cool if the manufacturers of this stuff would clearly explain how to use it? I know, that's asking too much.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  14. #14
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    Quote Originally Posted by trailville
    But Rock Shox calles it a "spring tube" therefore it must be one.
    Where do they call it a spring tube? I think there is in a spring INSIDE the tube. In any event, yes, the description here IS a good one in terms of it's functionality.

  15. #15
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    Quote Originally Posted by kapusta
    Where do they call it a spring tube? I think there is in a spring INSIDE the tube. In any event, yes, the description here IS a good one in terms of it's functionality.
    I recall that a lot of the advertisements for the Black Box motion control refer to a "titanium spring tube" as on upgrade over the plastic spring tube of the regular moco, and I think they call it a spring tube in some of their tech documents. But I was kidding about "therefore it must be one".
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  16. #16
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    Well some of the forks come with the pop lock feature (or used to) and in that case there was a spring in the moco tube! So technically in that regard I guess they could call it a spring tube on the pop lock models, I only know it because it was a real pain to disengage that spring, that was until I figured out how to unscrew the plastic moco tube and just pull the spring out!

  17. #17
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    Quote Originally Posted by kapusta
    Just keep in mind that the plastic tube is not really a spring. I believe that misconception has been sorted out since this thread happened 4 years ago.
    Never mind this post. I have since realized that this is essentially a correct explanation. I question whether it can really compress 1/4" (I've put it in a vice and it takes a LOT a pressure to get it to compress anywhere near that) but yeah, it appears it does not to compress for the FG to do it's thing.

  18. #18
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    Here's a link to the thread where "Bad Mechanic" provided an excellent explanation of the spring tube.
    http://forums.mtbr.com/showthread.php?t=590678
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  19. #19
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    Bump for good read

  20. #20
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    **re-bump** superb reading
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  21. #21
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    Sorry for thread resurrect!

    Good read. Im pretty new back into mtb after around 10 years sat in the pub, so am having to learn fast!

    As part of a second hand bike rebuild I ended up with an old 289 Tora.

    Could anyone give me a little setup up advice please to get me started? As ive just replaced the rebound damper as it was shot, and found an argyle MoCo unit cheap on ebay (30 new!) so have installed that. It has the internal floodgate adjust.

    It has the preload (not U turn) coil, yellow so soft. Im a fairly little guy around 165/170lb (no scales in house due to wife...) so its possibly a tad soft, however I have sag set to about %25/30 and it feels about right.

    On the other side I have rebound currently set to 'just slow the rebound a bit'.....

    Its the compression damping/floodgate Im struggling with a little... I mainly plan to ride XC/trail, im getting a little boring and old (er), so jumps and drops dont feature much. Its mainly bridleways Im riding at the moment, lots of loose stones a few inches in size, some roots etc.

    So from what im reading I should maybe set floodgate around 50% and use the compression damping seting to just remove a bit of brake dive? I dont need it overly fine tuned at this stage, just a good starting point.

    Thanks

  22. #22
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    Things have changed so much.

    In short.. motion control sucks pretty bad. Run your floodgate about 1/4 in, it's sort of useless past that. Then run your compression full open. If it's a smooth steep climb, maybe try half closed. It'll still spike full open.

    A lot of people felt it was hard to dial it in because it honestly just never works too well.

  23. #23
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    Does the current line of RS forks or the newer version of Motion Control hold up to a different or better standard than the days the post was started ?

    I've only read a few few reviews here and there but some were fairly complimentary on bike reviews that had a RS Recon (more specific to the fork on the bike) and I think that's not far up the ladder in their line up.
    Maybe comes on $900 to $1500 bikes.
    "Before you criticize, you should walk a mile in their shoes. You'll be a mile away from them and you have their shoes"

  24. #24
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    The major difference is some of the newer forks got a real shimmed rebound damper. The compression side is largely the same.

  25. #25
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    To clarify about the spring tube. Yes it is a plastic spring and has to compress for the blow-off circuit to work. But it does not function, perform or last like shims do. Nor is it tunable like shims are.

    People riding in areas which work suspension hard find the DNA spring tubes crack after 12-18 months. The older red versions seem to hold up much better.

    I'd recommend anyone purchasing a fork who needs suspension to avoid the moco and if you want Rockshox go for their RCT damper. The RCT looks similar but actually has shims inside. The shims can flex without breaking.

    If you want a bigger fork then the Lyrik or Pike with charger damper are far better than the Moco Yari. Even if you find the Charger harsh you can revalve and modify it. You can't do anything good to retune a moco.
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  26. #26
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    I bought a 2016 SID RCT3 and trying to understand better how it works.

    Beside air preload and rebound, there's the 3 position open-pedal-locked knob and a LSC dial. From what I've read, the LSC only works when the fork is in open position, and that I can use the LSC dial to minimize brake dive when running open.

    Running 15% sag, I go can only go through 90% of the travel (which is fine since i like to keep a buffer for the time I'll inevitably underestimate a drop), but the LSC doesn't seem to have any effect when triggering brake dive on purpose, there's no difference trough the full LSC dial range. I was expecting a more significant response from it, which leads me to think that it's really gonna be a either do-nothing adjustment or a fine tuning that will require several hours of trails over several weeks to notice the difference in LSC adjustment. Maybe I should run the fork with more pressure ? 60psi at 120lbs rider weight, but the fork really does great although uses a lot of travel even for smooth stuff, however doesn't feel like I'm wasting energy up front at all. Concerned that too little sag will actually restrict the fork, but currently I get too much brake dive on technical descents and wondering if it's my LSC adjust that is defective or if the fork just doesn't behave like I would want it to in full open.

    I like the idea of running half open, but does this apply to the RCT3 pedal mode ? Is the pedal platform mean to be used on technical descents with 1-2' drops at low speeds ?
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