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Question, I have a brand new RockShox Super Deluxe Coil Select Plus, Rx Trail Tune shock off a 2024 Spec enduro. I was gonna sell it..BUT my 2023 yeti 160E has a cavitating Fox X2 ( I know, Surprising..😆). I have never been happy with that X2 even as a Fox fanboy. To get the soft top then midstroke support I want I was still blowing thru the travel like crazy..Even with 3 volume spacers and set in the 30% progression setting. I ride hard but it was just Long Island NY( not the crazist trails). It may have been a dud from the start..But, I feel like I should try this RS coil, With the HBO. At least till I get the X2 rebuilt. My fox is 205/65 trunion, And the RS is 205/60 trunion, But it has a 5mm plastic spacer below the rubber bump stop. Should I clip that out, Or does it not matter just to try it out? Also Fox and RS hardware for the spacers and shaft thru the lower eyelet is still the same, Right?
I made a standalone thread before I noticed this one exists, figure here is the best place to ask this:
Do shock manufacturers intentionally design the IFP charging mechanism in a way that requires a special tool or adapter? Is it to ensure riders need to go to a bike shop for a nitrogen recharge? Most people I have asked say charging it with normal air is fine, since air is 78% nitrogen anyways.
I asked grok and most of the reasons it gave for this design choice seem a bit weak. I don't imagine it's significantly more cost effective than a shrader valve. Maybe its slightly smaller but that also seems like an issue that could be solved easily w/ engineering choices. Perhaps a shrader valve leaks more than the pellet system, but if it could be filled easily then it wouldn't be much of a problem.
Rock shox enters the chat.
All you need is an adaptor (it's cheap) and a shock pump. They say it's perfectly fine to pump it up with ambient air.
Fox is complicating things needlessly. But their products are rife with complications and proprietary tooling that changes every generation.
About 50 to 100 euros worth of tooling will cover at least 2 generations of RS products service procedures. The Vivid is a bit special, but the super deluxe series and the forks are a joy to work on. You don't need special clamps as parts have flats machined into them so you can grab them with a vice. Shafts have leading chamfers to mount sealheads so you don't need seal bullets. Etc.
Still doesn't fully make sense to me though. Why even need an adapter, why not just have a second shraeder valve for the IFP?
The more I think about it the more it seems like companies intentionally do it to prevent users from doing IFP pressure themselves. The most generous reasoning might be, that they assume most riders could get confused and fill the IFP thinking they are filling the air can? Clearly labelling the valves could fix that though.
If you clip the spacer out your HBO needle wont engage correctly. I wouldn't do it but you can run it on the bike and just have a little less travel than you had before without doing any harm. I think you can use the fox top hats on the the RS shock but you have to push the DU bushing out.
Is it a pressure thing? Schrader valves have a limit to their max pressure, depending on the configuration
There's probably a few reasons -
A full size schraeder valve will reduce frame clearance or IFP volume, and both are usually at a premium already. Picture below is a DVO with full size schrader, vs a Fox X2 cap
The sunken schraeder design like rockshox and new fox shocks is actually a standard part - its the same thread as inside a regular schraeder and is also ubiquitous in the HVAC industry. So the adapter is easy to find is fine to use with a standard shock pump
I like the pellet sealing systems, it does seem to give a more reliable seal and isn't that hard to use
And theres a good chance it is to add friction for someone to play with it themselves. It's not very useful as a tuning tool, but dropping it too low will cause your shock to pump full of air in no time. It's also very confusing when you pump it up to 200 psi then screw the pump back on to check and its more like 120psi....due to the small volume.
And yes people will/do confuse it with the air spring, or think its something they "need" to check
This is my probably controversial take, but charging the IFP is not hard at all....the tools are very commonly available with the bare minimum of searching for 99% of shocks out there. If you find that too much of a barrier then you possibly aren't ready to be rebuilding your own shock sorry. But they really aren't that hard to find so if you want to do it you can go ahead and get stuck in!
Fox does have a bunch of unnecessarily proprietary tools and procedures for their shocks, but the IFP tool isn't one of them. The coil shocks are mostly doable with simple tools (not the new DHX2 though)
Lastly - a gentle reminder for people that when your shock gets squishy/noisy, that is aeration or air mixed in to the damping oil. It is NOT cavitation - which is when the oil inside gets pulled under a vacuum and boils, creating a pocket of gas or gas bubbles inside the oil. They can make noise (sometimes a whistling or knocking) and return to normal at slow speeds. A cavitating shock will likely become aerated in short time though as the vacuum will pull air past the shaft seal.
Yeah thats correct - losing 5mm of stroke doesn't matter to try the shock out anyway
Ok here is the first example of pressures inside the shock and what changes when you tune the base valve VS changing the main piston. The first picture is the compression damping of the 2 different arrangements -
Both are quite firm tunes, that are similar-ish in overall damping rate. The blue line has a firm tune on the main piston with a softer base valve and lots of free bleed and the turquoise line has a firmer base valve and moderately stiff main piston. This is a pretty extreme case but it shows the best difference in what happens inside the shock. Neither are really ideal, the Turquoise curve is "safer", but there is a bit more hysteresis and would probably feel a little harsh with maybe not as much support at very high speed. The lines have a gap because the damper makes a little more force as its slowing down compared to speeding up.
Second picture is the measured pressures inside the damper as it goes through its compression cycle.
X-axis is time, as it moves from a (momentary) stop at the bottom to stopping at the top. The rebound stroke is clipped off at each end. Y-axis is pressure and force (Newtons and PSI - they are in a similar range for the different lines hence no separate Y-axis for force).
Purple is the damper force you feel at the shaft, orange is the pressure in front of the piston and red is the pressure behind the piston (rebound chamber). Turquoise is the reservoir/IFP pressure.
If you increase the pressure inside the whole shock, its only acting on the area of the shaft so you need a huge pressure to get any force. If you have a lower pressure behind the piston, that difference in pressure acts on the piston area, which gives more damper force for a smaller change in internal pressure.
The "safe" tune causes both chambers to rise - creating a peak around 450psi which is not too bad but if you wanted to go stiffer or as the shock reaches higher speeds, the massive pressures can cause damage to the seals, harshness or can produce a knocking sound/feeling
The stiff main piston has a much lower peak pressure (300psi), but the pressure behind the piston drops dangerously close to 0psi, which is where cavitation occurs
Generally, if you stick with the suggested tunes from a manufacturer they should be similar to the "safe" plot (probably a lot softer though) and you will be safe to add more damping at the main piston. There could be some outliers there, I'm still testing different brands but from what I can tell as long as you stick to the correct IFP pressure and use their supplied tunes it should be pretty safe. Since they are normally quite soft to begin with, if you try adding too much stiffness at the base valve it will create some pretty massive pressures to get the desired damping!
Dang thanks for the thorough reply! That all makes sense to me. I do agree it's not all that difficult to do if you have the motivation to get er done, but it's still not as easy as most other things on an air shock.
I have a separate question since you seem to be quite knowledgeable regarding suspension stuff. That issue where the shock pump hose fills with air when it connects to the IFP/air can and gives a lower psi reading. It's the act of re-connecting that gives a lower psi reading right? If I fill it to 200 psi and then disconnect my pump, I can trust it's still at 200 psi?
Just wanna make sure so I don't have any issues out on the trail.
I made a small air chamber with a schrader one side and a gauge the other to test my shock pumps for accuracy (I was bored).
What it also illustrated with my 3 different shock pumps was that there is no loss of air when disconnecting/unscrewing the shock pump chuck.
I could see a situation where if the rubber seal in the end of the chuck is perished or permanently compressed that you could in theory lose some air before the chuck has disengaged the schrader poppet.
Yes. The pressure "dropping" on reconnect is the air pressurising the hose. Same mass of air has to fill a larger volume which obviously means a drop in pressure.
Checking the pressure I mount the pump twice and add the delta between the two values to the first value to get the pressure that was in the shock initially. It's not exact but I think it's good enough.
Awesome thanks!
This is a follow up to a reply from @TEAMROBOT in a comment about the new RS shocks, because it relates to the pressure post above.
The top plot is a recent super deluxe (theres a few variations on the tunes, coil and air, high flow or not high flow piston but they have similar trends) set to fully closed, middle and fully open. In the firmer settings you can see how the force builds until the base valve opens and the line flattens off. In the bottom line there is no distinct knee which means we can assume it isn't building much pressure at the base valve. This design gives a lot of range, and probably quite noticeable but its more like a high speed adjuster. Because there is little pressure from the BV in the full open setting, you can't add much damping at the main piston either. It might be fine if you only ran in the firmer positions but there would be trouble if you set it fully open. It also has not much change below 127mm/s which is your body control/stability range. In my experience this range of adjustment gives an "OK" range, but you need to trade off support, bump absoprtion and bottoming control a lot more.
The lower plot is a different shock where the LSC dial has more change down to 25mm/s so the BV is doing much more work. From reading the press release it sounds like the new RS shocks will be somewhere closer to the bottom plot - maybe not the same, but if they can drop the IFP pressure to 120psi that signals to me a pretty big change
This was great. Thank you. I think I mostly understand-ish.
Oh yeah one other thing - I described the base valve as too "soft", when actually the shims are probably quite stiff, hence the large change in force available, its just they add too much extra free bleed or bypass when you open the LSC dial.
Also one small note about reading dyno graphs - the sharp bends in the curves look like valves open at a very distinct point, when actually thats just a PVP (peak velocity plot) graph which runs several speeds and only takes the peaks to make a single straight line. So the RS graph looks like the valve opens at exactly the same speed, when they would really open somewhere between that speed and the previous one measured
Slick move. I'm going to integrate that. Thanks man!
Yeah I often do the same if I need a more accurate measurement and not sure of the pressure change in the exact shock. Usually forks and shocks all change similar amounts but it you're testing something significantly different then its a good way to do it
This might be of interest to the readers of this thread, methinks: https://www.vitalmtb.com/product/guide/forks/ohlins/rxf38-m-3-68486#product-reviews-764016.
I hope everyone will forgive a very basic parts and maintenance question, but it does relate to suspension modifications.
I run SKF dual compound seals and an aftermarket damper (in this case, a Lift) in a Lyrik. I'm trying to figure how to replace the bushings and seals on the air spring. The 200 hour service kit is $75. I don't want the dust wipers and don't need the damper parts. While it'd feel wasteful and gross, I could just buy a new air spring for a tad over $90 and throw the old one away.
Am I missing something? What are people doing?
You can just buy the o-rings (and 1 quad ring) from a seal supplier and replace the ones on the current air piston and sealhead. Measure it for yourself, but its normally a #213 quad ring on the piston and a 10x3 o-ring against the shaft. The wiper there is normally fine
Or just buy and air spring and sell your old one to someone wanting to change travel. And if your fork isn't already buttercup equipped then you get a buttercup upgrade at the same time (assuming its a recent lyrik....otherwise disregard that part)
Huge thanks for that. Really appreciate all the knowledge you share on here. I'll pick up some o-rings and change them more regularly to boot. I remember your post about them degrading from time alone.
And just any old o-rings of the proper size will do? There's nothing special about them? You sure they're not aerospace grade?
My fork does have buttercups. Do you have any thoughts on how important it is to change out that little elastomer and with what frequency?
Yeah just Nitrile N70 o-rings (sometimes called NBR or Buna-N) - some places only do quad rings in N80 but thats fine too. Either way they are all extremely common standard Jellybean parts. You will occasionally seen Viton and Polyurethane o-rings but they are still easy to source if you really need it (just more expensive) but the majority of push bike products don't need anything that special and operate within the range of Nitrile. Shock wiper seals are often polyurethane for extra durability though
Couple tips on o-ring sizes, which is helpful if measuring and knowing what to order-
*Like most things imperial sizing is very common, so when I say a #213 o-ring (or Q-ring) the 2 means it is 3.53mm cross section. And the second 2 numbers relate to ID so a 214 is the next size up from 213. #1 is 2.62mm and #0 is 1.78mm
*There are a few metric sizes, like 1, 1.5, 2 and 3mm. So normally when you measure a seal it won't line up exactly with one of those or the imperial sizes, but factoring in that they stretch or compress slightly, you just go with the next closest one. ie if you measure one at 1.7mm or 2.9mm, don't go looking for that size - they were originally 1.78 and 3mm.
*The ID of an air piston seal will grow slightly, so if it looks like you are in between 2 sizes, go with the slightly smaller one. 99.999999% of the time they only come in standard increments, and most major brands use standard sizes. It only seems to be smaller brands that use weird sizes, as though they didn't fully factor that in during the design process (normally they would design the seal housing etc around the appropriate size seal for the application, but a few brands seems to miss that part.....like they make the seal housing and then find the closest seal that fits, even if its a weird size)
*A shaft seal might compress slightly, but generally the easiest way to know you've got the right size, is the ID of the seal will match the shaft size (eg a 10mm air shaft uses a 10mm ID o-ring) Installing it in the sealhead is what compresses it slightly to squeeze the air shaft.
Buttercups - in theory they do break down but I have noticed variation in them even from new so probably doesn't matter that much. I also believe their main benefit isn't really to do with absorbing bumps directly, but they correct misalignment in the same way as Fox's new glidecore springs. I still don't if Rockshox intended that or would ever admit it, but thats the hypothesis I'm sticking too until I get proven wrong!
I bought this DVO used for $75 and it gave me two strong seasons out of it. Worth servicing, or just buy a new shock? Compression is blown.
Probably not...those ones used a 10mm shaft which wasn't super durable, so you will likely need at least a new damper body and shaft on top of the service. There's a few updates/revisions you would need to look out for when its apart, so if you send it to DVO it should go OK but not everyone is that familiar with them...And you might find it doesn't last very long
The dampers have potential but the newer Gen 3 shock with a 1/2" steel shaft is a lot more robust so would be worth servicing, but the older ones you need to be careful with
Good to know.
It was a great shock, felt fine and just worked. I know the weight of the ebike can make any shock feel good, but this one genuinely did. Never felt it packing up, and never bottomed hard (until the compression blew and it bottoms hard on everything now)
Will a charger 3 (or 3.1,3.2...) RC2 fit inside a SID35 chasis? I have a frame lying around that will do with a 120, or even 110mm travel, "light" fork, but xc dampers are not my cup of tea, and a Pike is not particularly light, at least on paper
Check the reservoir pressure with a shock pump before you consign it to "blown", they were notorious for leaky valves and no pressure in the system feels the same as blown.
Good call out. Any idea what it should be?
I was going to link you to the service manual but forgot over the years that in hilariously DVO fashion...bruh, we totally spaced on including the 'pressurize the bladder' step in the published service manual. 🤪
From memory it's 150-180psi
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