Fox 38 air spring in Zeb chassis?

I ordered one. I think it’s going to be frame depending. I’ll check once it arrives

Did you get any Insight here? 

FYI MRP recommends adding 3-5 psi to your normal air spring pressure when you install a Noken. I setted on 5 psi to get my sag and midstroke feeling similar, and that's worked great for me, allowing me to bottom out when it was virtually impossible before.

What length were you running on your Zeb? 180? was wondering if the noken something I should start recommending folks on Zebs in general.
 

I've got a TruTune in a Lyrik I'm running at 160 (wildly progressive) with a Lift damper.  TruTune feels like it's made a very positive difference.  According to their marketing copy:

TruTune makes the air spring less "progressive."  This is what everyone focuses on.  

But it seems like what it's really doing is making the spring less sensitive to shaft speeds.  Air springs get harder to compress at higher shaft speeds.  It's the result of the air molecules not having enough time to dissipate heat, and seems pretty damn complicated from a tiny bit of research.

TruTune reduces this.  So when you install a TruTune and add 5-10psi, at slow to medium shaft speeds (e.g., braking and berms) you are getting more support in the first 2/3 of the travel from the increased air pressure. Then when you smash into something larger at high bike speed and get higher shaft speeds, the spring spikes less and you use more travel - i.e., it mitigates the higher air pressure.  

If you didn't add air, you'd keep your current levels of support at low to medium shaft speed and just make it easier to access full travel.

TruTune shows a graph (with both axis labeled, no less!) depicting a less progressive force curve, but they don't tell you the shaft speed.  Regarding the effects of adiabatic compression, they claim "The stiffness of air for high speed compression is up to 40% greater than its low speed stiffness."  But again they don't give you a shaft speed for that number.   

Are those numbers at the shaft speeds I create when I'm scared, off the back, and dragging brake or are they Amaury speeds?  Or are those shaft speeds higher than those actually produced by a bike?  Selling a fork product to the masses, they really ought to be quoting a number at a shaft speed of 4-5 m/s.  

In trying to fact check TruTune, I couldn't find anything in a few minutes of googling other than confirmation that the speed sensitivity of air springs is a real thing for mountain bikes.

1. 2010 paper on shocks. I would think that the smaller volume of the shock would make it more susceptible to adiabatic compression than a fork, but that's a WAG based on nothing other than uninformed gut instinct.  

"A" and "I" are theoretical.  At unrealistically low shaft speeds for full travel (top graph), the measured compression forces are close to Isothermal.  At 2.5 m/s, which is on the higher end for a non-pro rider but pretty realistic, you get pronounced adiabatic effects.

2. This comment from Steve at Vorsprung regarding the pitiful compression damping of GRIP2 dampers: "Depending on the size of the impact, it's very common for the fork to have more thermopneumatic* damping (damping from air temperature change during compression/rebound) than actual hydraulic damping."

* I got zero clue on adiabatic vs thermopneumatic.

Where did you find that info?  I couldn't find the manual on the site and the box didn't have any paper instructions, just the satchet of grease.

We were just in Christchurch for crankworx and Rode my 38 factory 170mm on 3 days, My 38 was all over the place For setup, it was great when cooler in the morning but it felt soft and 'packing down' in the heat( was quite hot but windy)

I've ridden ZEB's here and I can never remember such a drastic change, Also Butter cups seem to of made a difference there as its quite fast and rough(ive ridden several ZEB's here) but Find it gives up its travel easily before hitting a progressive wall but more consistant than the 38 was.

Side note: I hate the idea of the 38's air spring.

 

Great point! Paging @NoahColorado. I've been testing the Noken for Vital and when it arrived I was texting Noah at MRP about setup, and he recommended bumping up air pressure. I suppose the info from our text chat probably isn't available on the website!

But adding pressure as you add air volume is standard practice in suspension tuning. If you reduce volume by adding tokens, you should also plan to reduce air pressure as well. Think about it in terms of volume differential. For instance, if you have the same fork with zero tokens vs. four tokens, each setup has the same diameter air spring plunger pushing the same volume of air into the positive air spring chamber, but the positive air spring chamber sizes are different depending on the number of tokens. It's the difference between pissing into the ocean vs. pissing into a teacup. The same amount of fluid will make a greater relative difference when added into different volumes of water (air is a fluid).

The same fork setup at 70 psi with zero tokens vs. four tokens, the 70 psi is going to make the fork with the smaller air volume stiffer at bottom out AND stiffer at the top of travel, e.g. the fork with zero tokens will sit way farther into travel at sag and the fork with four tokens will sit much higher at sag. Thus, if you only want to adjust for bottom out resistance and you want the two forks to sit at the same sag point, you would set up the fork with four tokens at something like 60 psi and the fork with zero tokens at 70 psi, and make adjustments for all amounts of tokens in between, e.g. 62.5 psi for three tokens, 65 psi for two, and 67.5 psi for one (these are made up numbers for a hypothetical fork). But using this made up example, if you go to -1 tokens by adding a Noken, you would want to bump up to 72.5 psi. I went up 4-5 psi when I added my Noken, but there were some other spring characteristics I was trying to tune for and wanted to try less sag.

If you can't get full travel on the zeb but you can on a 38 you're probably feeling the difference in lower chassis volume. The cartridge style air spring of the 38 increases the chassis volume over the zeb. 

I think a lot of people overlook the ramp up of the trapped air in the chassis since it's just at ambient pressure, but it can actually create a pretty good amount of force.  

Especially for forks with more travel (e.g. 180-190mm), because an even larger volume of trapped ambient air (from running the stanchions farther out of the lowers at full travel, relative to a shorter travel fork) is being smashed into the same size space when bottomed out.

Yeah, what Charlie said is true. But, it's hard to give a blanket recommendation on air pressure with Noken vs. what you normally run because we don't know what you currently run – maybe you have dropped your pressure relative to stock settings already just trying to get full travel. Plus, there are a couple different generations of air springs for the Zeb, and their pressure recs (and progressivity) are different.

But yeah, going from no tokens to Noken, you'll prefer either your current pressure or slightly higher pressure. Going from any tokens to Noken, you'll definitely be upping your pressure.

I've been rolling like this with the hardtail for a couple seasons with no issues, albeit in shortish travel configurarions (full 27'5" at 140mm, or mullet with a cut down shaft at 125mm-ish) you'd get neumatic top out with most forks anyway, I think the spacers and rubber bumpers are there just for safety, I will avoid to do this in a setup any closer to the maximun allowable travel though. Thats the most linear, better felling fox 36 setup I have ever feel, but I particularly dislike that fork in stock form.

I don't think it's recommended but it works for me, its a cheap way to further play with postive-negative volume ratios. Proceed at your own risk of course, as I don't want to get sued, haha!

Very interesting. Took me a second to realize what you did, but for anyone who's wondering, he cut all the rubber bumper assembly out of the negative spring to add volume to the negative chamber without taking any away from the positive side (in addition to adding a Vorspriung Luftkappe). Here's what that 36 air spring would have looked like stock: