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Vorsprung-Suspension's posts

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May 28, 2014, 10:49 a.m.
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Joined: April 16, 2014
Understanding Suspension: Cavitation

not sure whether this was a psa or a rant… either way i appreciated it!

so vs, i have a question about emulsified oil - what's the symptom/how would you know if this is happening? i've been riding a shock recently that starts making a "frothing" sound towards the end of hard and fast descents, which seems to be accompanied by a decrease in control.

would it make sense that the oil has emulsified/is emulsifying under these conditions, and this is affecting damper performance?

Half/half PSA/rant - mostly just an explanation to clear up a common misconception.

Emulsified oil requires that you have air in your damper that is not dissolved in the oil. All oils can dissolve a certain amount of air; the amount of air (or other gas) that can dissolve in the oil is linearly proportional to the pressure the oil is under (this is called Boyle's Law). At atmospheric pressure (roughly 13.5psi absolute pressure depending where you are), your oil does contain a tiny amount of air dissolved in it: THIS IS NOT A PROBLEM. Air that is fully dissolved in your oil becomes "part" of the oil, and your oil viscosities are measured with air dissolved in the oil.

Let's consider the difference between a solution (as in, when air is dissolved in the oil) and an emulsion (when air is mixed in the oil). When any substance is properly dissolved in another substance, it is broken down to a molecular level, whereby the solute (substance that is dissolved, in this case air) is evenly distributed throughout the solvent (substance in which other things are dissolving, in this case oil), and due to the tiny mass of air that can be dissolved in oil at atmospheric pressure, has negligible effect on the properties of the oil. That is to say, dissolved air doesn't pose a problem.

An emulsion, however, results from the mixing of two substances that are unable to dissolve in each other. This results in bubbles/droplets of one forming in the other - for example, if you mix oil and water, you will see that they distinctly do not dissolve in each other but rather the oil sticks together and the water sticks together. If you forcibly mix them around, you will break up the oil and water into smaller droplets but they will still be emulsified - consequentially they will separate easily. The same thing happens with air - after the oil has dissolved however much air it can dissolve at the pressure it's under (which is very, very little at the pressures we're talking about), all you can do is mix large bubbles of air in with the oil. If you keep on mixing (ie your suspension keeps moving), the bubbles will stay somewhat mixed in with your oil, but if you let it sit for a while, the bubbles will all rise to the top and your oil will de-emulsify itself for the time being.

When such an air/oil emulsion is forced through a damper's valving, you will get very rapid (hundreds or thousands of times per second) changes in the damping force being generated, as air and oil have massively different densities and viscosities. What you feel this as, is commonly perceived as a slightly "rough" damping feel when you bounce on the bike, as though your oil has tiny grains of sand in it. This is most noticeable in emulsion dampers such as the Mission Control and Motion Control systems used by Rockshox.

Now, to answer your question directly: if your shock doesn't sound airy or make any noises when it's cold, emulsification of your oil probably isn't the issue. If it has air in it, you may be correct, in which case it's time for a service. For emulsification to occur during a run, your damper needs to have air in it (the amount that dampers can suck in over time is quite small and takes a relatively long time, air is not coming and going every run). If there's no air in your damper, what you may be noticing is the way the oil noises change due to the change in viscosity as the oil heats up - between 40C and 100C (very much a realistic operating temperature range for rear shocks), even the best oils will drop to between 25-40% of their original viscosity. With shimmed dampers this actually doesn't affect high speed damping very much (long story worthy of its own discussion) but it has noticeable effects on your low speed damping - most noticeable in that your rebound speeds up and that your low speed compression damping can feel like it's more open than when you started your run.

Ultimately though, the easiest way to tell whether your oil has become aerated is to open the damper up. When we service shocks, it's common to see anything from zero bubbles, to literally an explosion of foam as soon as you crack the damper open. For things like Boxxers, take a 24mm flat wrench with you on a ride one day, and pull your compression cartridge out as soon as you stop riding (even after 20 seconds of riding). You'll probably be surprised by how foamy the oil is.

May 27, 2014, 11:38 p.m.
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Joined: April 16, 2014
Understanding Suspension: Cavitation

CAVITATION: What It Is, And What It Isn't.

You will commonly hear people in the bike world refer to cavitation in the context of suspension. The simplest possible technical explanation: cavitation is when a small amount of your damper oil temporarily turns from liquid into vapour because of very low pressure (aka vacuum).

This occurs when the pressure drop over a damper piston equals or exceeds the gauge pressure in front of the piston. This is caused by any combination of high damper shaft velocities, insufficient gas charge pressure or insufficient pressure drop across base valve relative to the piston/midvalve pressure drop. To translate that technical description to something a bit simpler: imagine your shock shaft/piston moving through the oil in your shock as it compresses. If you were able to compress that shock fast enough that the pressure forcing the oil through your piston/shim stack couldn't keep up, you would draw a vacuum behind the piston, at which point a small amount of your oil would vaporise in order to fill the gap. This is cavitation: the point at which oil pressure behind the piston hits the fluid's vapor pressure (essentially once a vacuum is drawn). The typical symptom of this is a sharp compression spike, followed by a knock as the damper changes direction between compression and rebound, at which point the shock will extend, moving your main piston back and compressing the vapour until the pressure builds sufficiently for it to return to its liquid state, at which point the piston "slaps" the oil as rebound damping kicks in sharply, since you're now forcing oil through the rebound valving rather than simply using the piston to compress a gas. Cavitation is STRICTLY a dynamic phenomenon - that means it only happens under set circumstances, whilst things are moving.

What cavitation is NOT: when air gets mixed into your oil, the oil becomes aerated and looks foamy. This isn't cavitation (or "cavitated oil"), this is the result of air and oil emulsifying (an emulsion is the mixing of two different fluids - yes, gases are fluids - that aren't soluble in one another). Air and oil mixing can occur for a few reasons:
1. Because either your damper is an emulsion damper (such as Rockshox's non-Charger dampers), where there is no physical separation of air and oil
2. Because your damper is an open bath damper (most Marzocchi forks for example), where once again oil is not sealed off from air
3. Because your sealed damper (all rear shocks, Fox FIT cartridge forks, Charger dampers) has either been bled imperfectly or ingested air (this happens over time in certain dampers).

In sealed cartridge dampers, air in the damper means service time, but in emulsion and open bath dampers, aerated oil is not a factor you can easily control. Most oils have anti-foaming agents in them, however these simply break down bubbles more easily rather than preventing your oil from getting sloshed around with air in the first place. In open bath forks with high oil volumes, it's less of a concern because the most heavily aerated part of the oil typically sits well above the inlet/outlet ports of the damper.

If cavitation is truly occurring (it's a lot more rare than the use of the word would imply), it is absolutely nothing to do with the "quality" of the oil you're using, it is a function of the damper configuration (including valving, gas charge, design etc). In other words, changing your oil won't fix it.

So next time somebody tells you that you've got "cavitated oil" or that your suspension problems are caused by cavitating, or that a particular type of oil will prevent cavitation, please be aware that what they're actually telling you is that they don't fully understand what they're talking about.

May 7, 2014, 10:37 p.m.
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Joined: April 16, 2014
Lyrik not getting full travel

there was indeed fluid all up in that air spring.

so when I reassemble, should I not follow the manual's suggestion to put 6ml of 15w in the upper tube and 15ml of 15w in the lower leg? Just grease? Many thanks

on pg 8
http://cdn.sram.com/cdn/farfuture/pY...e_manual_0.pdf

15ml of 15wt in the lowers is correct, but wiping a bit of Float fluid (I don't recommend using any other oil for that) or some slick honey on the main piston seal, plus a bit of slick honey on the o-ring in the seal head, is all you want to do in there. Putting any measurable amount of oil in the air spring makes things worse rather than better. While you've got it apart, it's worth changing out at least the dynamic seals (seal head and main piston) too, as those are wear items.

May 3, 2014, 10:17 p.m.
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Joined: April 16, 2014
Lyrik not getting full travel

Coming from a fox fork previously, I tried a couple ml of float fluid on top of the piston when I rebuilt the lyrik. Bad idea! It moves to the negative chamber like Vorsprung explained. It makes it super harsh, the fork felt like crap. Rockshox recommend to use only grease instead and I would avoid oil altogether in there. FWIW, it felt like it made the seals swell as well, the piston didn't move freely when moving it by hand with the air spring disassembled.

If there is no oil in there and every thing looks good, I would look at the o-rings around the baseplate and shaft. Basically the same ones as for the OP, but on the spring side. It's a pretty basic air sping, there is not much that can go wrong and you said you looked at the valve already.

Hope it helps

Good advice in general. A note on this - there is only one oil I'd recommend using to lubricate air spring seals and that's Float fluid, but all you want to do is wipe a bit of it on the sliding surfaces (seals and piston/bushing), not pour it in there (except in the case of Float forks as you mentioned), as all oils do interfere with the volumes of the respective air chambers. If you don't have access to Float fluid, slick honey grease is the other option (non-silicone-based greases also not recommended). Other suspension oils are much too thin to do the job and will result in things feeling comparatively sticky. However, over time grease simply gets pushed out of the way and stops lubricating as effectively, so it tends to be a shorter-term solution than a lick of Float fluid.

May 2, 2014, 11:39 p.m.
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Joined: April 16, 2014
Lyrik not getting full travel

Solo Air. At normal riding pressure it has very bad sensitivity on small bumps but medium and big stuff feels fairly normal. Tops out harshly. It feels pretty much the same as a Dual Air fork with pressure only the positive chamber.

probably too complex to be asking about here but any tips would be appreciated, thx

The first thing I would do is pull your Solo Air assembly apart and check whether much oil comes out of it. It should have enough oil in there that the surfaces of the air piston and topout bumpers are a bit "wet" but no more - it should not have enough oil in there to pour out as such. If there is any substantial amount of oil in there, it will take up volume in the negative spring chamber, meaning that as soon as the fork compresses, the pressure in the negative chamber will drop extremely rapidly, causing very high stiffness early on in the travel. This can be caused by improper oil volumes installed in the air spring during servicing, or by oil migrating from the lower leg lubrication. In either case, drain the oil from the spring, replace the air shaft seal and rebuild with the correct oil volume in the lowers and only oil-moistened surfaces in the air spring.

May 1, 2014, 11:50 p.m.
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Joined: April 16, 2014
Lyrik not getting full travel

How about a Lyrik DH that doesn't seem to accept any air in the negative spring? Everything else functions fine. I've opened it twice and checked that the internal valve works and that everything is in place. Any ideas before I pop a new spring assembly in?

Cheers

Which spring system are you using, and exactly what are the symptoms? How does the fork behave when you try to compress it at your normal riding pressure?

May 1, 2014, 1:10 a.m.
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Joined: April 16, 2014
Lyrik not getting full travel

I have the same exact fork and had the same problem a few months ago. For me, it was the exact opposite of what vorsprung said, it was the damper oil leaking into the lowers. You will find out when you remove the lowers, there was a LOT of oil in mine. I replaced the o-rings around the baseplate and rebound shaft, problem solved.

This is another common situation, based on failure of the same seal, however the reason I suggested migration into the damper originally was that the OP said the damping adjustments were working correctly (though from a later post it would appear that isn't the case). As the damper loses oil into the lowers, the compression adjustments typically stop working at the start of the travel.

My understanding of hydro-lock was simply that there was too much oil (or contaminates) in the lower legs, I guess there's more at play. Sounds like I need to pull the fork apart today and have a closer look.

Hydro-lock can occur in any chamber (ie your lowers or your damper cartridge) that has too much oil in it. The easiest way to be certain which it is, is to drop the lowers. If more than ~15ml of oil comes out, you have damper oil in your lowers. If no oil comes out but the damper cannot be compressed fully whilst still in the stanchion, bath oil has migrated into your damper (this is particularly common in Fox FIT cartridges and many air spring systems).

Looks like you nailed it. Pulled the compression assembly, oil is approx 2.5cm below the bottom of the valve head - guess I know whats up now! Must have really let go in the last ride however since before yesterday the compression adjustment was working fine and while the fork felt a little funny, it wasn't a major issue.

So what exactly do I need to get this thing operational again?

Assuming that by valve head you mean the compression piston (opposite end of the assembly to the topcap), then your damper is losing oil either through the topcap (unlikely since you'd see it) or into your lowers. Drop the lowers and you'll know for sure.

In either case, the required work is the same - you need to replace the rebound seal head o-ring. You can purchase a Rockshox service kit (parts lists are in their relevant technical manuals on their website) and fully service your fork while you're at it, or for certain forks you can just buy the seal head itself (includes new o-rings) or you can get the o-ring from an industrial supplier provided you can accurately measure the size. If you haven't got experience measuring up seals, I would recommend just getting the service kit or seal head so you can be sure you've got the right parts.

If you're not comfortable doing the work yourself, feel free to hit us up, but if you don't want to mail your fork off, chances are there's a local shop who is capable of doing the work too (your location says you're in the Kootenays - Sacred Ride in Nelson would be a good start).

Hope that helps!

April 26, 2014, 9:57 p.m.
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Joined: April 16, 2014
Lyrik not getting full travel

Over time, the seal head on the damper side (the seal that separates your damper oil from the oil in the lowers) can allow oil to be drawn up into the damper. If you drop the lowers off the fork, you will quite likely find that you are unable to fully compress the damper side alone, as over time (since most people change the lower leg oil many times before ever checking the damper) it has drawn in oil.

At this point, it would be a good move to service the damper and especially replace the rebound damper seal, though be aware that almost any seals that are cycled at high speeds under reversing pressure gradients will tend to allow for some degree of oil migration like that - in other words, it'll happen again over time.

April 21, 2014, 12:34 a.m.
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Joined: April 16, 2014
2014 fox 36 talas RC2 160mm reviews?

That does sound like way too much pressure. I was running 55 or so in my older Talas 36 but I am only 142 pounds. Converted it to float and I am running about the same. I gather the new Talas is a lot different then?

The new TALAS cartridges use a smaller diameter piston than the old ones, hence the need for higher pressures. Whether a system requires higher or lower pressures isn't really a big deal in terms of suspension performance, it's simply a characteristic of the spring geometry itself.

The old TALAS systems used a mechanism that changed the pressure equalisation point between positive and negative chambers in order to adjust the soft-topout point of the fork (same thing the Rockshox DPA system does). This requires three sliding seals, as well as a couple of dozen (yes literally) other static seals and check valves. It was a complex system that was also rather finnicky to fix if anything went wrong - got better with each generation but I don't think many suspension service centres around the world ever celebrated when they heard a customer say "Hey guys, I have a problem with my TALAS cartridge…" :)

The new TALAS spring system is equivalent to having a Float system that you can extend or shorten the length of. The negative spring system is the same as the Floats, and the way it adjusts travel is to effectively lengthen or shorten the length of its outer tube (which in Float forks would be the stanchion itself, in TALAS forks it's a separate tube).

There is no question that it is a superior performer to the older system, but as the forks haven't been on the market all that long yet we'll have to wait and see how reliability goes - hopefully better than the older TALAS. It has less moving parts, given that the travel adjust mechanism is now quasi-static so it's reasonable to be optimistic. The only problem with waiting to see what reliability is like in the bike industry, is that by the time we find out, there'll be something newer and better on the market anyway!

Steve

April 21, 2014, 12:05 a.m.
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Joined: April 16, 2014
Fox 32 progression tuning

Adding 5ml at a time of Float fluid is the easiest way to tune the progression. Keep track of how much you've put in there though, as each time you service it you'll have to refill it.

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