The Tuesday Tune Ep 9: Single Tube and Twin Tube Dampers - Video

 Thanks for the kind words! The videos are really just a way to start a conversation - we try to keep them short enough that people don't find them overly tedious, but we can't simplify decades of suspension development down to 10 mins and be thorough, so the discussions afterwards are really good for covering what people want to know more about.

 Just to make sure I wasn't full of it, what do you think of these claims? You sort of cover the second one, not sure about the first.
Ohlins claim on TTX 22M Universal: "The twin tube design allows the gas pressure to always backup the low-pressure side of the piston to keep pressure at a controlled level. This ensures consistent damping performance on all types of terrain and improves damping response to give outstanding control of the bike and tire movements."

Cane creek: "Exclusive Twin Tube Technology circulates oil continuously through the damping valving to achieve highly controllable, independent damping for both compression and rebound strokes. This unique design moves oil through externally adjustable valving instead of the main piston, allowing for superior tunability and eliminating the need for internal valving changes to achieve proper shock setup. "

 @sarahlh: What they claim is objectively true and subjectively debatable. The Ohlins claim is objectively that the twin tube design prevents cavitation, which is true. Subjectively, they claim it gives "outstanding control" - that part is realistically determined by the actual damping curve more than anything, and it's only an advantage over a shock that does actually cavitate or have a substantially larger pressure drop over the base valve than the main piston.

What CC claims is objectively true in their description of how oil flows through the damper, but again whether it's "superior" or eliminates the need for valving changes presumes that the shape of their damper curves and the obtainable characteristics are actually exactly what you want them to be. Given that Ohlins run quite a linear rebound curve (as touched on in the video) in the TTX across its range of adjustment, like many single tube shocks, they are realistically competing on a few factors:
1. Friction - they're good but a little stickier than the CCDB (comparing coil to coil)
2. Cavitation - not an issue in any stock shock currently available, save perhaps one from a particular French company
3. The specifics of the compression and rebound damping curves - this really is where the difference in performance come from, and the curves attained by Ohlins and CC are entirely achievable with a single tube shock IF the designer/builder deigned to construct and configure them that way.
4. Hysteresis - super important in road racing and largely unimportant in mountain bikes due to the very high velocities.

 @VorsprungSuspension: "IF the designer/builder deigned to construct and configure them that way. ". Do you see evidence in the non-twin tube shocks you list that they are indeed building them that way? And if yes, are they configurable such that they can reflect different damping curves as other variables might dictate (rider, terrain, conditions)? I hope I'm understanding what you're saying enough such that my second question makes sense.

 @VorsprungSuspension:

Hi, what do you think of reduced breakaway force as an advantage of twin-tube dampers? The lower oil pressure and (potentially) narrower shaft should result in a lower spring force from the damper and therefore a lower breakaway force (quite apart from the lower friction). Do you think this advantage is realistically measurable or significant?

Thanks!

 double post

 @VorsprungSuspension: do you mean that the bird-like noises from my Stoy are in fact cavitation? Is that due to a low ifp pressure? I recall that the shaft was quite easy to push through its travel before mounting the spring...

 a lot like what Rock Shox is doing with Metric and Trunion!

 @sarahlh: @sarahlh: you're definitely asking the relevant questions there! To answer your questions in two parts: broadly, yes single tube shocks are configured however the designers see fit, and that can include, for example, anything from digressive rebound curves (X2, CCDB, Jade, most RS shocks etc) to progressive rebound curves (Elka Stage 5/MRP Raze, latest generation RC4 etc) and anything in between (ie linear, which is quite common). Some companies outside the bike world, for example Penske, provide different pistons for a single shock to allow for progressive/linear/digressive damping curves right off the bat. However, most manufacturers, including some of the more boutique "custom" shock builders, use only a single piston design per shock, which in most cases means you realistically have one or two of the three basic curve types (progressive/linear/digressive) available in each direction. This is of course assuming a fixed "mode" - some dampers have mode selector switches where you can flick from open to firm to nearly locked out, and obviously each of those modes has a different characteristic, but in most cases they are increasingly digressive.

 @Happymtbfr: @Happymtbfr: the BOS shocks are super low friction and run at low IFP pressure because they attempt to balance pressure drops across main piston and base valve quite precisely. Cavitation can occur if you run zero HSC on those with certain valving configurations.

However what you're hearing is not cavitation (which would be noticeable as a sudden harshness followed by a knock as it changes direction into rebound), it's the canary stuck in your shock

 @ilikeallwheelsizes: Compare a first gen RC4 (15.9mm shaft) with a CCDB coil (8mm shaft) and you'll notice a very large difference in how easy they are to initiate movement with by hand (spring removed). The spring force at 150psi in the RC4 is in the vicinity of 45lbs at topout, vs about 11lbs in the CCDB.

 @VorsprungSuspension: thanks for your answer, I will try to not forget feeding that birdy!
And nice haircut by the way!

 @Happymtbfr: In my experience the sound comes from air that has leaked past the IFP into the oil of the damping circuit. I thought that wasn't good so it was time to have it serviced.

 @vinay: did the noise disappear after servicing the shock?

 @Happymtbfr: Yes, it went quiet. I understood that it was important to have it done as air in the oil could cause damage to the internals.

 @vinay: ok thanks

 @Happymtbfr: I have to add that this wasn't a Bos Stoy shock or even a piggyback layout. It is the 2007 Magura Hugin shock which has adjustable HL compression damping and low speed rebound damping. Not sure if that matters much. I wasn't that aware of the existence of the expansion chamber in such a shock without piggyback, but apparently there is a small chamber with a 50bar gas charge pushing the oil back for the rebound stroke. I'd expect these piggyback shocks have a larger expansion chamber with a larger diameter piston, so I expect a lower pressure hence a smaller urge for the gas charge to leak into the oil. But still, if the symptoms are similar chances are the cause is similar as well.

 @vinay: thanks for giving more info! It makes sense

 Didn't quite understand what you meant by that, can you elaborate?

 @VorsprungSuspension: just would love to hear your thoughts on the vastly wide array of price differences between the different shocks

 @preach: Shocks like the Rockshox Kage, for example, are cheap and cheerful, fairly basic shocks constructed with budget in mind. Ohlins at the other end of the spectrum are substantially more expensive because they have very complex machining going on, a lot of secondary and tertiary finishing processes on all the surfaces, custom seals, and a large amount of R&D expense behind them. The Kage aims to be a "real" damper at the lowest possible price, the TTX aims to be the best damper possible that people might actually pay for. That variation is pretty well always the case with any range of products.

 @VorsprungSuspension: I think he means between the ccdb and void and vivid and x2? at least that's the way i saw it

I can understand the ohlins being more due too publicly more R&D however could you not say the same about the other companies its just there's is not as public if you know what i mean?!

And by no means am i an expert or have any knowledge of shocks whatsever, i can service one but that doesn't mean much

 ...and Taco Tuesdays!!

 Or a 3D rendering/cutaway?

 Sorry, I did kind of assume people understood what was going on at each of the valves/main piston. There's a LOT of details inside a shock for sure. Check out some of the other videos in our blog - if you have a look through them all, particularly the very first one where we compared the CCDB Air and the Float X2 side by side, I think you'll probably find the explanations you're looking for.

 Twin-tube shocks in the passenger vehicle world are cheap pieces of crap basically - emulsion dampers built as cheaply as possible. Turn them upside down and they stop working! Monotube shocks in the car world are basically the equivalent of the cheapest, most basic shocks in the mountain bike world, in that they're actually sealed and pressurised. When we refer to twin tube shocks in the bike world, we're talking about shocks based on Ohlins' TTX concept, which was developed at the MotoGP/F1 level, not at the "we make these shocks for $12 each" level

 @VorsprungSuspension: I'm pretty sure there is a lot that'll quit working when I put my passenger car upside down. Suspension will be my least concern .

I'm currently running a Magura MX shock in my fully, which if I understand correctly is basically a scaled down shock Conti uses for lorries. A similar design is also being used by Porsche on certain cars, but I'm not sure if their version might use some addition oil damping. By your explanation it qualifies as a twin tube design as the damping fluid (air in this case) cycles in a single direction. Then again all compression damping is done by the shim stack in the main piston. It is basically three chambers with the outside two connected through the push rod. During the compression stroke the rolling lobe rolls up (so volume reduces there) and drives the push rod through the other chamber so volume reduces there too. The middle chamber expands hence the air goes through the shim stack. During the rebound stroke the air goes through a port back into the chamber with the rolling lobe. Downside of course is that damping is very limited, upside is that there is no friction and it doesn't need any maintenance.

I'm most interested in the one that uses the air chamber behind the IFP as the main spring. I forgot the brand, but you might recall it. What's your take on that one? Nearly as simple as the Magura MX shock I mentioned, equally limited adjustability but I heard it performs really well.

 Avalanche Downhill Racing does that when they custom tune X2s and DHX2s. They add a speed sensitive piston and shim assembly that's tuned for you and your bike.

 Ohlins do on the TTX22. Depending on how much oil flow is forced through the base valve vs the main piston (ie the relative stiffness of each valve, which is to a substantial degree affected by how much hysteresis you deem acceptable), the base valve may need to allow for a lot of oil flow (as is the case with Cane Creek's configurations) or the main piston may allow a lot of oil through to the extent that little more than the displacement of the damper shaft is forced through the base valve. If you need a lot of oil flow, a poppet valve can allow that more easily than a shim stack for any given body diameter.

TL;DR version - because of the little details.

 @VorsprungSuspension: I finally got my CCBD air working "pretty good", by making the main/shaft piston compression stack fulcrum much smaller, in the effort to reduce HSC forces. Worked pretty good but it still needed more HSC flow.

 No reason you can't separate the adjustments to a similar degree in a single tube damper. Twin tube dampers typically have a more effective HSC adjuster, but you could build an identically effective adjustment system in a less space-effective manner with a single tube.

 Funny how different our settings are for the same bike and shock. I weigh 77kg, 500lb spring, HSC-2, LSC-3, Rebound-5. All are from open. I do have a 650b link which changes things. I agree on adding a click of HSC for jump trails. I add a full turn or two of LSC for long smooth climbs. Compared to my CC inline the TTX is better in rocks at speed. I wouldn't think that is a function of the coil vs air but rather the damping or maybe the bottom out bumper?After a demo ride last summer I also think the 11-6 is going to be a solid step better.

 Out of the shocks currently out there, yes, the twin tube units from Fox and CC have the widest ranges of adjustment. If you understand how to make good use of those adjustments, that can be great in order to get them set up. Twin tube dampers are definitely the in thing right now, but as with all things there's a certain amount of perception and marketability that affects that.

Also, the reason Fox currently use twin tube dampers may or may not be related to them having poached a former Cane Creek employee to design the DHX2 and Float X2, since they don't make twin tube dampers in any of their other markets that I'm aware of

 @VorsprungSuspension: I agree that marketing can be used for evil purposes (spinning a story instead of educating the consumer) and the MTB world has far too many meaningless acronyms, but riding is believing -

poaching talent is only a thing if you don't believe in free markets -the real question is did they violate any patents? every industry shares talent but just the fact they would want to hire someone to do a twin tube product tells me they either believe in the technology or at the very least they feel they have to have that product to be marketable or competitive-

 @keyth-mpls: for sure - in no way am I saying their products aren't marketable or competitive, or that twin tubes have no merit at all, just discussing all the factors at play. Fox are not amateurs, nor are Ohlins, and while marketability is always a factor I do think they'll always use what they really believe is the best approach at the time, even if down the track they change their mind or new developments change things up.

 Just a note about my experiences. I'm right at 200lbs, and of all the rear shocks I've ran, the most recent worst performing shocks were twin-tube(CCDB Air and Fox Float X2 Air). I am basing this "worst performing" description by the fact that both these shocks were tuned for the Specialized Enduro, and out of the box, had WAY too much High-Speed compression damping. At 200lbs and riding at a mid-pack Pro level in local races, and having a suspension engineering background, I expected these two shocks especially to have a wide enough range of adjustment to feel great, and they did not. I re-tuned the CCDB to work OK, but never played with the X2 before I sold it. For reference, the Monarch Plus Debonair out of the box feels WAY better at high shaft speed, than both the X2 and CCDB. The Ohlins STX single tubeair on my 2017 Enduro feels WONDERFUL.

 @thuren: I'm gonna assume since you have a suspension engineering background you setup the shocks correctly

- but what makes you feel like the stock setting and adjustment on the HSC was way too high?

you describe your self as mid pack pro - were you racing XC?

 @thuren: Interesting - I felt that the X2 was over dampened on my Santa Cruz nomad and my coil felt a 1000x better. I started to work on getting spring rate correct and messing with LSR and HSR and found they were surprisingly effective at achieving a race pace feel that I desired. It may be a result of pedaling platform feel The S and SC were aiming for. I setup the HSC and LSC settings similar to recommended an spend a month adjusting them a bit with with combinations (bracketing) with the rebound settings and finally found a stable HSR and LSR that allowed for the small bump high shaft speed feel and big hit rebound I needed. It was a bucking bronco for a while and was either too harsh off the top or kicking me forward on hits... @VorsprungSuspension

 @keyth-mpls: I can confidently say that when it comes to setting up suspension, I am well above average at doing it haha.

High-speed compression can spike pretty hard if the shock does not flow enough oil with the valving/damping design wide open. I call this maximum orifice flow. Basically if all the valves are as wide open as mechanically possible, any damping forces added by the orifice flow would be damping spikes. Main piston port flow, channels leading to/from the pop-off valves, valving/pop off travel, fluid friction, etc. The CCDB and Fox X2 had a high shaft speed "harsh" feel. As noted I did not pull apart the X2 to see if I could modify, but main piston flow improvements and lighter CST oil helped the CCDB a lot.

I placed 4th pro in my last enduro race last year. XC is not my thing at 200lbs and short legs haha.

 @nicolai12: I had to run my X2 Air at 40% sag to let the my rider weight/spring rate ratio push through the valving, and it was still harsh on high shaft speed hits.

I had both the high and low speed compression basically all the way open and it was still harsh, IMO.

 @thuren: I sell and setup suspension products for a living, your comments strike me as a little odd - I'll explain-

It is very rare for someone over 200lbs to complain of too much HSC damping (yes I understand what HSC is)
generally the complaint is not enough or not enough noticeable difference in adjustment

basically what is happening is on an impact (the compression stroke) the shock is not moving fast enough for you to be comfortable or your wheel is not maintaining traction, right?

When I start to troubleshoot I usually find 3 things:

1) The air pressure / or spring rate is not set right (or preload) and one is too high (oversprung)
solution: reset pressure or spring rate to get proper sag (enduro and downhill guys want to do this standing up on the bike pedals)

2) LSC is too high and the rider is interrupting the pedal platform as a loss of suppleness or too much HSC
solution: open up the LSC adjuster

3) The bike just doesn't "feel right" usually because it doesn't feel like their old bike which was not setup right to begin with
solution: spend some time getting use to the correct tune, try doing a run and changing 1 adjuster 1 click - trial and error for several runs until optimal setting or track times acheived

For the average rider it is very hard to discern the difference between spring rate and HSC damping
Basically the spring (air or coil) should be doing the heavy lifting in the impact stoke - HSC is just adjusting the timing

If HSC spiking is truly the problem - Im thinking lighter weight oil would be the next step

Keep in mind -even with data aquisition tuned pro bikes, maximum comfort is not the same setting for maximum traction for racing - Does that all make sense?

 @thuren: that just doesn't sound normal for your weight - perhaps there was something in your shock blocking flow - I have seen tuners pull staples and other warehouse debris out of shocks before

 @keyth-mpls: Thanks man! I agree with most of that for the average joe. I don't set my bikes up to be comfortable I set mine up to be fast, and handle big hits at high speed.

I just looked you up and looks like you are in Central Oregon too!

Here is a vid of my little 5.5" travel 29er getting down Bachelor.

www.instagram.com/p/BJs1zw1DdVZ/?hl=en

 @thuren: @keyth-mpls agree with keyth...also at 40% sag you're well into your travel and it's beginning to become progressive - maybe take a look at the number of volume reducers in there and reset sag to 30% and double check your LSC and HSC and go with factory recommendation initially and make a 6 click change to only one at a time and find the balance. Sounds odd.

 My guess is that it's because damper shaft speeds and inputs/disturbances at the wheels are relatively slow in mountain bikes.

 @sull0253: sorry, that is not correct. Hysteresis by definition is a system's state's dependence on its history. That is not limited to valve opening/closing variation, which are measurably tiny with any shimmed valve due to the limited valve displacement, but is typically defined as including any cause of lag in the response of generation of damping force at any given velocity. Valve open/close characteristics, oil compressibility, damper elasticity, check valve closure, check valve shim flex, o-ring/glide ring shift, flow development and friction all contribute to that, though you are correct (and was stated in the video) that the higher flow rates correlating with large displacements result in higher forces at lower pressures. In fact that was pretty much the major point regarding twin tube dampers.

Not sure where you're getting your info - the digressive HSR "claim" has been demonstrated on our dyno. It is the nature of any preloaded HS circuit that it is inherently digressive unless the circuit never opens. The CCDB and X2 poppets don't open as suddenly as some valves since they have tiny little shims on the nose of them to prevent flutter, but the digression is there and measurable nonetheless. Not opinion, just fact.

 @mdhorner hysteresis is really important on road racing vehicles because they need to generate high damping forces at very low velocities and low displacements in order to control load at the tyre's contact patch very precisely. By contrast, mountain bike shocks have long stroke, move at very high speeds and need to generate relatively low damping forces. The maximum velocity that some of the F1 guys even dyno their shocks to is only barely beyond the velocities at which the HS circuits in some mountain bike shocks are beginning to open. Very common to see the F1 guys running max velocities of ~0.2m/s vs anywhere from 1-4m/s max velocities in MTB shock testing, but they need very high forces at those low speeds.

 @sull0253: What is your background and what are your sources?

 @sull0253: if you think that's all Hysteresis describes, you should hit the books a bit more.

 @sull0253: While in theory a twin-tube or recirculating shock has the flow advantage, I find that most designs I have played with are still very restrictive in High-Speed compression. HSC is where they SHOULD out perform a more conventional design that is pushing ALL the oil through the piston. This would mean that the restrictive Twin-Tube retains the high pressures and possible drawbacks. Recirculating/TT shocks still have valves, shims, and possible cavitation which can induce Hysteresis. Pushing the majority of the pistons displacement through recirculation valves at high flow rates mandates some HUGE valves are used. There is a reason Twin-tubes/Recirculating designs still use shims on the main piston.

 @thuren: so is all the complexity any better then a well designed piston/shim stack shock? What I see as an advantage of twin tube/ poppet shock is on fast high speed washboard where pressure drop may cause cavitation (hysteresis) but there are MX shock (shim stack) that have over come this ! What I am saying is a properly valved MX shock design is hard to beat!

 @sull0253: you're an clownshoe buddy!!

 @MX298: That is tough to answer. If I could start from scratch and design a twin tube, I think I could create an easier to adjustable/better functioning shock than a standard smooth body shock. That said, it's tough, as I like a bigger diameter piston for more displacement, and with a twin tube you are stuck with a smaller piston. Pros and cons to both really!

 @MX298: at some point it all comes down to economics - if designed from scratch, you can make a singletube or a twin tube design perform so close to identically that the distinction disappears, if money/weight/packaging are not an issue. But those things are always an issue

 @VorsprungSuspension: so why all the effort to make a poppet/twin tube shock when a single (shim/piston) shock is cheaper and easier to service? Not like we're controlling a 6,000 car with 750hp, it's a human powered machine . . . . . . They just seem very complex for what we are controlling!

 @MX298: external adjustability of high speed rebound, easy ability to have wide adjustment range, perceived advantages of lower hysteresis and marketability would be my answers, but you'd have to ask the guys designing them. There are other legit reasons you could use a twin tube design that I have not seen implemented in the bike world yet.

 @sarahlh: Good question. What if it turns out I designed the majority of products currently being discussed. And what if I was unsuccessfully trying to mitigate the proliferation of inaccurate information being spread by a self proclaimed suspension expert who bought a few text books and a crank dyno. Bit of irony?

 @sull0253: OK the crank dyno comment is funny. 10 IPS for the win!

 @sull0253: hahah passive aggression FTW. In spite of the years of formal study, the undergrad thesis, the R&D, the practical experience and the measurement, I'm always keen to learn more from anybody who's got something to teach me, but if you're going to be rude and condescending, please take your comments to Youtube where they belong. In the meantime Devon, for somebody who works for Rockshox as a suspension designer, I'd suggest it might be a good idea for you to revisit some of the theory that you've incorrectly tried to call us out on - I stand behind everything said in this video in spite of the fact that it's a 10 minute summary of a complex topic. Maybe asking your PR department about how to represent your employers professionally in public wouldn't go astray either.

@thuren: even our little 3VS goes to four times that... as stock. With a bit of imagination it's not too hard to push things a little further with a few modifications, until you run into power limitations. For sure it's not as nice as an EMA or hydraulic dyno, but it gives you the vast majority of the useful information at a price that is orders of magnitude lower.

 @VorsprungSuspension: You're right, I should not have been rude. However, spreading this inaccurate information is still dangerous. I designed these shocks for very specific reasons that take time to explain where you've deviated. I apologize for not taking that time. I'm also not legally allowed to debate these issues publicly although feel free to contact me PM if you're truly interested in learning.

 @sull0253: Appreciate that, thank you, however unless demonstrated otherwise I am not aware of any error in what was said in this video (ambiguity perhaps - like I said, these are short summaries). Regardless, if you find yourself up in Whistler at any point, by all means come say hi at our workshop, always down to talk tech!

 @VorsprungSuspension: I just thought the "crank dyno" comment was funny is all not busting your chops. I think all of us suspension guys love watching these video's, trying to poke holes in what others in the field say, and I agree with pretty much everything you discuss.

I don't "specialize" in bike shocks, but I imagine 10-40IPS is VERY helpful in verification of lower flow systems that are so helpful in the feel of bicycle and moto suspension.

I have been tuning off-road truck shocks since the crank dyno was the only way(unless you were Ohlins 10 years ago I think they were first right?), so I did not use them because they did not tell me anything. Doing the work and real verification was the only REAL way.

 @sull0253: Well maybe you are learning that there are still things to learn? Just because something is designed a certain way, does not mean that the designed shock was executed the best way it could be. You'd be implying that all these shocks we are discussing are perfect out of the box for everyone, and most notable, that they are reliable, never had updates, recalls, or design revisions. I can't tell you how many times I have opened up these bike shocks and thought to myself that the engineer was nuts.

 I wouldn't be patting myself on the back and getting into internet arguments if I was a designer at RS.... Like above, everyone has more to develop and learn, and no suspension product to this day is perfect, especially in cycling.

 @VorsprungSuspension: thanks Steve for the info! I enjoy it and it always brings up more questions. From the MX side where weight and space are not so much an issue mt. bike suspension is quirky sometimes. Seems Fox stuff (with some vorsprung) stays together as all the RS stuff fell apart, also got a truck with Thuren stuff too. Good stuff guys ! ! !

 The Shock Absorber Handbook by John Dixon or the Racetech Motorcycle Suspension Bible by Paul Thede are the go-to texts for this stuff.

Regarding maintenance - design/manufacturing quality has more to do with it than anything. Shocks with higher gas charge pressures actually typically last longer before the oil becomes aerated, counterintuitive though that may seem.

 @VorsprungSuspension: Thanks for the advice. Looking forward to next Tuesday!

 What you're feeling may be the air equalisation port - feels like a notch a few mm into the travel. If this is the case, nothing wrong with it per se. Forgive me if this seems spammy, but we do make replacement air sleeves that, in addition to being substantially more linear than the OEM units, do not have that notch, if you're interested.

 @VorsprungSuspension: Sounds pretty good to me. The clunk at low speed feels so horrible. Otherwise (as long as I add air to shock once a week), it doesn't actually feel too bad.

I think I'll definitely be sending you guys an email to see whats what. I also have a 2015 Fox 36 RC2 that could use some servicing and maybe some input from you guys. I currently run over 90psi in the fork and some people think that is way too high; I'm about 210-220lbs.

 Such systems have been made. I have heard that the guys at Suspension Centre in Switzerland had such a system years ago in a 40, though I think it was only ever a prototype. Would there be a benefit? Potentially yes - but difficulty of tuning is a big part of that. If you could use such a system to simplify tuning, then sure, but if it was confusing the rider even more then obviously that wouldn't be helping.

 The IFP charge is there for a few reasons - it allows damping over the main piston (up to a certain pressure drop), it provides variable internal volume so that the oil displaced by the shaft has somewhere to go (otherwise the shock wouldn't be able to move), and it forces oil back into the damper body when the shock is rebounding. The compression assembly in the bridge is there to provide further control over the compression damping, and it is an accessible place to put an external adjuster (which is harder to get to on the main piston, especially if you already have a rebound adjuster in there).

 @VorsprungSuspension: Awesome, interesting stuff! Thanks for your help. So what do you adjust, compression-wise? The valve sounds one-way to allow oil flow on rebound, so I guess spring preload?

The idea being that without somewhere for the oil to go, compression is impossible; With a large empty cavity for oil to flow into, compression is easy; Somewhere in between those extremes (an expandable area that variously resists expansion) you can control how easy it is to compress?

 @WaterBear: basically the damping adjusters all have some effect, directly or indirectly, on the hydraulic flow area that the oil is being forced through. The smaller the area that the oil has to flow through, the greater the amount of force required to push it through at any given speed. This is what creates the resistance as a function of velocity, which is what damping is.

 @VorsprungSuspension: Got it. Thank you very much! All questions answered.

 The bladder/IFP thing isn't especially relevant to performance, it's only for the purpose of reducing friction, and its effect is not especially large, on shocks with smaller shafts.

However, every little detail varies between those two shocks, so I'm not entirely sure whether you're asking a hypothetical "could you make this layout perform as well as that layout" or "does shock A with layout X work as well as shock B with layout Y". The answer to the first question, from a design standpoint is "similar enough that you couldn't tell the difference by feel", the answer to the second question is that they are constructed and valved in different ways that reflect the differing tuning philosophies that each company typically espouses.

 @VorsprungSuspension: Thanks for the information. To help clarify, I was wondering if both were tuned for my frame and I specifically, would there be any advantage in grip to running a twin tube style damper over a monotube? I'm trying to decide between a Jade or a TTX.

 Isn't the Vivid air sort of the same design as the above? Could be wrong.
This says it's a twin tube design: www.sram.com/rockshox/products/vivid-air-r2c.

 @sarahlh: the Vivid dampers are a very oddball twin tube design - they work almost the exact opposite of the Ohlins in that they're really only behaving as a twin tube in rebound rather than compression. Not entirely sure why they chose to do that other than to have an external HSR adjustment.

 @VorsprungSuspension: Because RockShox. That's why.

 @VorsprungSuspension: As far as I can understand it is to separate beginning and end stroke rebound, they also call it like that. With their design that seems possible (I have never touch a Vivid, I am talking just from internet pics...)
Separating beginning and end stroke rebound looks sensible to me, to separate, grip/stability requirements(end stroke r.) with "over the bars from kicker" (begining stroker.)
May be I am completely wrong...

 @Guarana2th: They do call it that, though their adjusters are simply low and high speed. This was explained in one of our previous Tuesday Tune videos if you go through our blog.