The Tuesday Tune Ep 3 - Air Springs and Volume Spacers

 LOL!!! Exactly

 aaaaaand cut.

 A coil spring extends to its manufactured length and stops, so it stores no energy at full extension. That allows rebound friction to ease the shock or fork to a stop - One of the main reasons they feel so supple in the small bumps, and don't "top out."

By contrast, an air spring has a huge amount of energy in storage at full extension due to its static pressure. A negative spring opposes that static pressure, reducing the stored energy to zero at full extension (in the best-case scenario) so the air spring will act like a coil in the first 25-percent of its travel. There is so little volume in the negative spring that it ramps up quickly at full extension and in reverse, becomes ineffective shortly after the compression stroke begins.

 @RichardCunningham: Thanks, this makes sense. I'm more asking about the location where equalization occurs.

For example, I know that on the Debonair can, the equalization point is somewhere into the stroke of the shock (which is why you need to cycle the shock after airing it up to let it equalize). My question is - wouldn't having the equalization point partway into the stroke rather than at full extension prevent it from being able to return to that full extension? Once positive and negative pressures are equal, the shock won't want to extend any further.

 Basically if your bike is particularly progressive in the early stroke (ie it runs a lot of sag) then the older style air cans will help control sag better for climbing, and they're typically a little less progressive in general so if you have serious end stroke ramp up from the linkage they can work better too. For anything else, higher negative volumes like the Corset will work better.

Positive and negative chambers don't have the same pressure in them at topout if they equalise at any distance into the travel. This works because the surface area of the piston on the negative chamber side is smaller than the surface area on the positive side. Force = Pressure x Area - we are looking for forces to be equal at topout, pressures need to be manipulated with respect to the surface area to deliver equal force.

 @VorsprungSuspension: Thanks. That answers both my questions. Cheers!

 @VorsprungSuspension: To add, you cover in detail how different bikes benefit from the Corset on your blog. It's worth a read, if others want to know more.

vorsprungsuspension.com/blogs/news/17562332-how-well-will-the-corset-work-with-my-frame

 I believe it has something to do with the different suspension designs,single pivot or Horst link etc as to what kind of shock suits it. An example is my own giant reign with the standard monarch rt.even with spacers it blows through travel so I feel like id benefit from a coil or air shock with a big negative chamber. Thats my understanding anyway!

 @SeanOg: A coil spring would not have the progression of the Monarch so it should be easier to bottom out. A different damping tune would be the best way to add support in my opinion.

 @kanioni:
My monarch has a MM tune,should I try upgrade it maybe?!

 @SeanOg: You could maybe get the current Monarch tuned at next service, if you have some suspension wizards around.

 I do. Evidently you get what you pay for

 In theory, no - the air spring curve is the same shape for everyone, it just gets scaled up or down by the pressure. However, in practice heavier riders find that the damper is not supportive enough in terms of compression damping, so they have an increased reliance on the spring, which means that they end up needing to run the spring rate disproportionately stiffer.

 @VorsprungSuspension: so does this mean us heavier guys should get a compression tune first before moving on to adjusting sleeve and volume spacers?

 @Travel66: which order you do them in is up to you, but if you're outside the "typical" 70-85kg weight range then it's definitely worth considering.

 @VorsprungSuspension: thanks and cheers for the videos!

 Well in part because it's easier to physically package them in a shock - with a fork you are effectively constrained to the size of the topcap and footbolt as to where you can put adjustments (notable exception being BOS's original Idylle which had the Stoy remote reservoir attached to the bottom of the leg). But things go in and out of fashion too, and manufacturers make arbitrary decisions as to what will be necessary or work best.

 Its for 90% of the users not knowing what it's for and not being able to make it feel like shit so the brands don't get blamed. I hoped that made sense

 Most likely yes - higher pressures in any air shock will typically mean higher rate of air ingestion into the damper oil. Higher IFP charge (where possible - not with Boost Valve shocks) helps negate this though.

 @VorsprungSuspension: Thanks for the insight!

 The same force at 3" travel concept was simply to illustrate a point - how you can separate the stroke into relatively independent components so that you aren't seeing too much crossover between what you're trying to achieve in the early and later stroke.

With any terrain there is always the need to balance support throughout the travel, so that it is proportionally stiff enough in each region. It's almost certainly going to involve some substantial inaccuracies due to the personal elements involved if we were to make big generalisations on terrain requirements, but it's reasonable to say that typically, the faster, steeper and rougher the terrain, the more your dynamic ride height is lowered which requires more support in the early/mid travel, that progression alone can't fix, and that the more big single hits you have, the more end stroke support you will need irrespective of the stiffness of the initial stroke.

 Bachelors in Automotive Engineering. It's basically mechanical engineering degree that is specifically focused on the automotive industry. I don't know a whole lot about the education system though as it varies a lot across the world - while I'm fairly certain there's no existing course in bike suspension, I believe you can get a PhD on almost any specialisation that is relevant to an existing academic field. In other words, I think you could do a PhD in bike suspension as pertaining to mechanical engineering, provided you generate a thesis based on a body of original research.

 Although not specifically pertaining to bicycles any thermodynamics or physics class will touch on this. Anyone who has a bachelors of science in any degree from the states should be able to recreate these graphs. I hope...

 @VorsprungSuspension: Hire me. You are a wealth of knowledge and explain things so simply and deliberately. Im a great PR guy

 @VorsprungSuspension: On behalf of the others that also benefit, I really appreciate you taking the time to put these out. It's a skill unto itself to simplify complexities for us less educated in such heady fields. Just ask popular astrophysicist Neil deGrasse Tyson. Y'all some smart motherf*ckers...

 If you want more bottom-out resistance without changing anything else in the early stroke (let's say first half or first 2/3 or thereabouts) then adding a volume spacer while slightly reducing pressure would do that. If you want more bottom out resistance AND a softer initial stroke, you'll want to reduce volume and pressure more substantially. It's definitely worth experimenting with - add a spacer and then see what pressure you need to run in order to not be bottoming out all the time. If that's still not soft enough in the early travel, then add another volume spacer and lower the pressure further.

 @VorsprungSuspension: thanks for the reply. It cleared things up for me a lot more!!

 I wouldn't recommend altering negative chamber volumes unless you have the means to alter the equalisation port location at the same time. Simply shrinking the negative chamber volume without changing the equalisation port location will mean your shock doesn't extend fully. The Corset and other high-negative volume sleeves do require higher pressure by design. If you're within the rating, you're within the rating - Fox's air sleeve seals are extremely good and rated to much higher pressures than they ever see even at their max pressure stated rating. Not every manufacturer has such robust seals though - there's a reason we don't make those sleeves for every shock out there.

 @VorsprungSuspension: I checked and the shock does extend fully with spacers in the negative chamber (rockshox monarch rt3) but are you saying that under compression the shock may not extend fully (return to full shaft length)?

I'm within the rating of 350psi but my shock pump doesn't go past 300! Negative bands was a band aid fix. Maybe I need a smaller sleeve or need to loose some weight

 @mrmatt: If that's the case then either the pressure in your shock is not properly equalised or it tops out firmly against the rubber bumper instead of pneumatically without the band installed. It may still be a net benefit for you however, but it's not the approach we prefer to take.

 @VorsprungSuspension: Sheeeet. Not to throw anyone under the bus here, but I blew the air spring this morning on my Monarch Plus Debonair after only a dozen rides. Seems this isn't an infrequent occurence and makes me wonder if I would have been better off with Fox. I do like the shock though and it was an improvement over my Float CTD for sure. We'll see how it holds up for round two.

 You're right, it can be measured without too much difficulty, however despite being relatively simple, it still takes time, money and effort to do (especially if you need to characterise every linkage out there too!). It's not information that anyone who has invested that time and money into measuring is necessarily willing to give away for free.

With that said, the graphs shown in the video were all force vs travel, not force vs spring rate

 @VorsprungSuspension:

Sorry, my comment was not meant to be a dig at you guys, more at the shock and bike manufactures. I'm just grumpy because I had to spend a couple evenings this week poking around inside my semi proprietary Scott/ Fox nude shock in order to figure out a) where the secondary positive air chamber was and b) how to custom make a volume spacer to fit so that I can actually get some decent ramp up and stop bottoming out or running 5% sag because of all the air pressure I need to run due to Scotts apparently regressive- linear - regressive leverage ratio on my bike that is published nowhere except on some crazy spaniard's website that I need google translate to read. That's the end of my rant!

 You're right, we'll make sure pressure, travel and forces are metric next time

 Old Solo Air forks did, yes. New Solo Air (in the Lyrik and Pike) is not quite the same.

 @VorsprungSuspension: Thanks for your answer!

 You can do that, yes - it really depends exactly what you are trying to change by altering your volume spacer config. I highly recommend working with pressures rather than sag in your fork, because it's difficult to precisely/consistently measure fork sag.

 @VorsprungSuspension: I guess what I'm trying to change is to minimize bottoming out on my fork. It's not to say that it happens that often, not every ride, but when it does it feels rather harsh, which shouldn't come as a surprise because it is a lot of force. It usually happens when I land a drop a little front heavy or at the end of a steep section that has a harsh transition. I check my travel o-ring regularly when riding and reset it if the fork has bottomed. I feel like the fork runs through the travel effectively using the amount needed for the terrain that I'm riding, it feels lively and doesn't feel like it's riding low in the travel, although small bump compliance could be improved at low riding speeds. I run a '15 Fox 36 HSC/LSC

 Hi Vaclav, sorry to hear about your negative experience. I do remember the shock coming in a while ago with some internal damage that was not apparent until it was opened up (gouged damper shaft if I recall correctly?) that happened to be the one size shaft that is Trek-specific and not able to be sold to us by OGC. I don't recall hearing back from you about the outcome from OGC though, and if you'd like to shoot me an email at steve@vorsprungsuspension.com we'll make sure your costs are covered and that you aren't out of pocket as a result. Once again, my sincere apologies for the hassle and frustration you've experienced.

 @VorsprungSuspension: Well damn Steve, way to outclass me on this post here. I feel like a jackass now. I appreciate the offer but everything worked out ok in the end after a tense back and fourth between OGC and the shop. It was just off-putting after hearing such great reviews of your business from everyone I know who's gone there and then have my shock situation go from zero to "voided warranty" so quickly. The crux of my frustration was hearing you guys voice concerns of submitting a shock to OGC disassembled and that it might cause warranty problems, and then ignoring your own concerns and handing me a disassembled shock anyway.

Given your epic customer service here (and thanks for the personal message as well) you have very much changed my opinion of Vorsprung. That was about a year ago? Year and a half? I'm surprised you remember the exact shock, because that's precisely what the issue was. I'd recommend you to just about anyone, but proprietary shocks in general, maybe not so much.

Thanks for the response and my apologies for airing my dirty laundry in public like this.

 @Vaclav: Thanks for the feedback - we made a judgment call on that and clearly we got it wrong, for which I apologise. We'd like to make it up to you somehow, so please do shoot me an email and we'll work something out.

Negative feedback is not a bad thing for us, we always want to be making our processes and services better, because if we are letting our customers down then nobody wins. If it happens that we get something wrong - and it does happen now and then, we are human - it's always good to hear about it from the customer so that we can reassess how we're doing things and make the necessary changes to ensure we aren't repeating our own mistakes. Of course it's always nicer for us, like any business, if it's done privately, but if we upset a customer sufficiently for them to feel that it's justified to air concerns publicly, then one way or the other we made a substantial error and we need to make amends, learn from it and do everything we can to prevent it reoccurring.

FYI we don't service most proprietary items (Brain, DYAD etc) - the DRCVs are an exception as the service kits are available to us, as are most of the internal parts (because most are shared with the standard Float series), but there are a handful of parts that distributor agreements prevent us from being able to purchase. Unfortunately in your case, the part in question was one of the ones we couldn't get. Had it just been a blown seal (as is the case in the majority of shock failures) it would have been no problem. The reason I remember your shock is because it was one of those "wtf, that's a new one" kind of moments - it was a type of failure we had not seen before and had not anticipated prior to opening your shock up.

What we have taken away from this is a change in procedure for handling these shocks - routine servicing is no problem and will be continued, however in future any problematic DRCV shocks will be referred to the distributor directly. That way we can make sure that the issues we caused you are not repeated for anybody else.

 Looks like a TPC+ damper curve... well other than the explosion part anyway! haha

 Not for sale sorry

 @VorsprungSuspension: Fair. Great video btw, thanks for removing the white noise. Keep them coming!

 @VorsprungSuspension: who said anything about buying it? I'll take it for free. =)

 @chrisingrassia: You can download the movie, save frames with plots, use ImageJ to fit curves by points, save points as x,y coordinates, fit point by spline or functions by Solver in Excel...star wipe....and you have your spreadsheet

 Depends on the criteria you're judging it by, and how it's going to be used! For outright sensitivity there is no going past a coil spring, because there's no seal friction or odd spring curves. However, air springs give you the ability to adjust early and late stroke spring rates quite separately which coil springs don't, and with that comes the ability to vary sag (for the sake of geometry) without necessarily running a spring rate that's way off base for the rest of the travel. For rear shocks you also need to consider the frame it's on - if it's particularly progressive, use a coil. If it's not progressive enough, air can work better. Also worth considering the type of damper you're using - that makes a big difference too. Comparing the performance of an inline air shock (CTD, Monarch RT3, DB Inline etc) to a DH spec damper with a coil spring really isn't comparing apples to apples.

 @VorsprungSuspension: Nice one I put an air shock on my devinci Wilson. I think it has messed up the small bump sensitivity but has maybe helped a bit popping off stuff. However can't slow the rebound down to the levels I was happy with when there was a regular coil CC DB Shock.