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VorsprungSuspension jamessmurthwaite's article
May 5, 2022 at 17:53
May 5, 2022
YT Replacing Capra Shred Dampers Due to Shock Failures
@yoitsrobj: Are the frames the same, or could there be a difference in stiffness causing a different failure rate? Because the only difference between the 2020 Factory and Performance Elite series of those shocks are the high speed adjusters not being there on the Performance Elite shocks. Every other part is the exact same thing. On the 2021 shocks, the Performance series do have different shaft/piston/eyelet assemblies though.
VorsprungSuspension jamessmurthwaite's article
May 5, 2022 at 17:41
May 5, 2022
YT Replacing Capra Shred Dampers Due to Shock Failures
@mattg95: trunnions and yokes aren't the only contributors to premature failure - a very flexy or misaligned rear end can have similar effects. We have seen plenty of failures of various descriptions (eg air sleeves burping under side loading) on frames using this extended-seatstay design in the past, but it's much harder to generalize about those because if the rear ends are built stiff enough that the misalignment can be tolerated by the eyelets, these problems don't necessarily occur out of proportion to the general frame population (likewise, trunnion frames that are well aligned and sufficiently stiff are not necessarily too hard on shocks, but in our experience these are pretty rare). @ohio is correct that sphericals would solve the issue here. The extended-seatstay setup does mean that under hard side loading of the rear end, the rear/lower eyelet of the shock is rotated one way (for example, clockwise if you're looking down at it from the rider's perspective) whilst being translated in the direction that naturally tries to oppose that (in this case, to the right as viewed from the rider's perspective), which effectively adds to the rotational load on the shock. If that displacement/rotation is significant it can be very hard on the shocks in spite of the eyelets being more tolerant of misalignment than say trunnion. However, with all that said, given the particular shock, it may not be entirely or unduly the frame's fault either.
VorsprungSuspension seb-stott's article
Mar 30, 2022 at 13:01
Mar 30, 2022
Review: Öhlins TTX2 Air Shock
@Crossmaxx: Haven't had one in my hands, but have taken a look at the design in some depth. Super innovative design, no question there, has some really cool features like highly integrated spring/damper, apparently quite good (though quite progressive) spring curve, low hysteresis (if you care about that - I don't), adjusters control the full amount of the oil flow, one less moving seal than a standard air sprung shock (sort of - it does double duty with the positive chamber also pressurising the IFP for the damper, but unlike most shocks it has no mechanical advantage so you get 1:1 friction from the IFP). The design has its limitations too - it needs quite high pressures for a given spring rate, pumps huge volumes of oil through the damper circuits (because the damper piston displacement is the same as the air piston displacement) which requires extremely high-displacement/low pressure valves, and without building a separate test unit, you can't dyno the damper separately from the spring. Oil expansion also directly impacts the spring rate in a more significant way than a normal shock. There's a few other design aspects that I think could potentially be problematic but without testing one properly I could not tell for sure. Overall though, I think it is the most innovative shock we've seen in some time, plus it looks cool as hell. However innovative design alone does not necessarily guarantee performance or reliability.
VorsprungSuspension seb-stott's article
Mar 30, 2022 at 12:39
Mar 30, 2022
Review: Öhlins TTX2 Air Shock
@Sshredder: Dual Air did work well and offered more tunability than Solo Air (ie self-equalising), but Rockshox moved away from it because the setup difficulty was causing more issues than it was worth. On a rear shock, the surface area of the piston on the negative side is about half what it is on the positive side. Most rear shocks have max pressure ratings somewhere around 300psi. In order to balance forces at topout, you need to be able to put in about double the pressure on the negative side than the positive side. On a fork, the piston area difference is only about 10%, so you only need about 10% higher pressure in the negative chamber than the positive. Curious what shock you're using that has a separate valve for negative air though, you said a SID dual air shock? The one from 20+ years back? I'm not even aware of anyone making such a thing currently. Those things definitely run a lot higher pressure in the negative chamber than the positive (or they have a TON of preload). The Giant NRS used those back in the day specifically so they could run it with zero sag.
VorsprungSuspension seb-stott's article
Mar 30, 2022 at 10:13
Mar 30, 2022
Review: Öhlins TTX2 Air Shock
@Sshredder: air valves on the negative chambers of air shocks could solve it, but you'd need a pump capable of about 600psi for the negative side. I'd be willing to bet with the shock Seb had though, you could bounce on the shock slowly a dozen times and have it equalize properly (likewise when depressurising it, slowly force it to full extension a few times) and have the shock completely rideable in the space of 30 seconds. Evidently it was actually able to equalise (just too slowly), or it wouldn't have been able to get air into the negative chamber to cause it to suck down when depressurised in the first place.
VorsprungSuspension seb-stott's article
Mar 30, 2022 at 10:09
Mar 30, 2022
Review: Öhlins TTX2 Air Shock
@ExMxEr: sounds like they cut it too fine to try to get rid of the notchiness and instead created a bigger issue - I'm not excusing it, just explaining the difficulties in designing/manufacturing what seems like such a simple aspect of the shock.
VorsprungSuspension seb-stott's article
Mar 30, 2022 at 10:08
Mar 30, 2022
Review: Öhlins TTX2 Air Shock
@optimumnotmaximum: machining leaves sharp edges on the port, which can cut the seal over time, which is why they're pressed (nice smooth round corners). Intend's shock design is completely unique, it uses manual equalisation and is not comparable to the more standard format that everyone else uses. A high negative pressure relative to the positive pressure actually increases the noticeability of the notch.
VorsprungSuspension seb-stott's article
Mar 29, 2022 at 16:56
Mar 29, 2022
Review: Öhlins TTX2 Air Shock
It comes about from trying to make the transfer port as small as possible so that people don't complain about the "notch" near the start of the travel, which can otherwise be noticeable when bouncing around slowly on the bike. In some cases, the backup rings on the main piston can obscure it enough that it can't equalise fast enough, and that's what causes the issues Seb was experiencing. It is a difficult aspect of shock design to get completely right because if the port is consistently big enough (being usually a pressed feature, not a machined one) then you're liable to get that soft spot/notch, or if you run it too close to the line, it's a pain to equalise. One way or another you're likely to end up with customer complaints and there is no straightforward way around it besides trying really hard to get the clearances right. Forks usually don't have the same issue because they mostly run plastic pistons (not backup rings) with clearance to the stanchion, lower pressures, lower pressure differentials, much greater displacements and usually have the equalisation port much closer to topout, all of which make it much simpler to make the port big enough without the rider noticing much in the way of notchiness. However, plenty of forks have in fact had difficulties with that in the past too.
VorsprungSuspension seb-stott's article
Mar 29, 2022 at 15:20
Mar 29, 2022
Review: Öhlins TTX2 Air Shock
@half-man-half-scab: When the air in the shock is compressed, it heats up, and that heat is then conducted away partly by the air sleeve (the degree to which it does that is dependent on how much time it has available to conduct the heat away), which reduces the pressure below the adiabatic ceiling (the maximum possible pressure it could have at that moment in time). When the shock then extends again, it's actually pumped some of its stored energy away as heat (same as a damper does) and the spring force during extension is lower than at the equivalent position during compression (this sounds like a lower spring rate, but in some cases it's actually a HIGHER spring rate, because we're seeing a greater change in spring force per unit distance). Over time (eg over the course of a descent), the net heat loss of the spring is actually insignificant (otherwise the pressure would slowly drop further and further and the shock would get softer and softer), because it does regain that thermal energy once it fully extends again, but the aluminium parts of the shock act as a thermal capacitor which effectively introduces a limited form of low to mid speed damping. I say limited in that there is a hard limit on the amount of force it can generate, unlike a hydraulic damper, and no direct control over it - and it's position-sensitive as well as speed sensitive, even for the damping element of the air spring. For that reason, coil sprung suspension does typically require more damping than air sprung suspension. This is one of the things we've grappled with for the past 10 years, and honestly debated whether or not to even discuss publicly, simply because it is so thoroughly confusing for people who don't have their head in this all day every day. Makes it exceptionally difficult to display accurate air spring curves too, because they're only really accurate at one velocity/displacement profile, but the most relevant and consistent spring curve to consider in my opinion is actually the most basic isothermal curve.
VorsprungSuspension mattbeer's article
Mar 15, 2022 at 23:23
Mar 15, 2022
Ask Pinkbike: The Best Whistler Bike, Tubeless Rim Tape, Dual Crown Enduro Bikes, & Converting to a 1x Drivetrain
@Tambo: Yeah, that force explanation isn't accurate at all. For a given force at the axle and a given axle to crown, both headset cups will see the same amount of force regardless of whether the fork is single crown or dual crown. You can't just "transfer" forces from lower to upper headset cups; they're a coupled reaction pair. Sum moments about either one and you can calculate the reaction force at both, which is the same regardless of whether the bending moment in the fork is handled by stanchions or steerer tube or both. What you can however argue is that the single crown fork is significantly less stiff, so certain impacts that are almost entirely energy-dependent where the fork can't move along its axis (such as nose casing a double) will generate significantly higher forces at the axle with a DC fork (because a certain amount of energy has to be dissipated by the flex of the fork; less displacement means higher peak force). This doesn't apply so much to heavy landings where the fork can compress because the axle force is limited by whatever the fork's spring/damper and friction will give as resistance. That, coupled with the possibility of damaging carbon frames near the headtube in a crash, means that the real risks DC forks pose are just crash damage or being ridden harder.
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