Air spring shocks (MTB Rear suspension Ep.13)

Hello guys! In this new episode I will deeply cover the air spring curves, and the contribution of negative & main chamber volumes to the final curve. As discussed in the video, a bigger negative air chamber provides a much better spring curve, with more initial sensitivity, more mid stroke support and more progressivity potential. Enjoy.
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[@SkillsWithPhil]

This was seriously well broken down and explained. I'll be refereeing people your way.

[@andrextr]

Thanks Phil :) BTW, your channel looks interesting! Subbed

[@zanetaylor7]

You two want to team up on a video over rockshox’s new Megneg air can? I’m curious to know when it is a good idea and when it isn’t.

[@kenobinai]

Think I watched 8 or more videos before this. Thank you, this is the best clearer explanation by far 👍

[@SchorschHackl]

I have to admit, that I never fully understood the typical curve of an air shock, even though I'm a technican in a similar field. Now I understand, very good explanation, never found so good information from the big manufacturers... Thumbs up!

[@KevinHering]

Great explanation about the value of incorporating a larger-volume negative air spring in shock design! I can see why it's important to choose a shock that fits your suspension design (esp leverage curves)! It would be nice to have tools to do this to help people get a great starting setup. Thanks for sharing your knowledge & expertise!

[@MtbEnduroChile]

Andre! Hi buddy! Take your like and share for your good work! Amazing video again, after watching it i made my investigation about the size of the negative air chamber of my upcoming shock! Thanks a lot for the info and keep it up with your great videos!! Cheers from Chile!!

[@andrextr]

Hola Germán! Gracias! Tengo visto tus videos de la mini escavadora jejeje that's crazy. Un saludo de Portugal :) Puedes hablar espanhol lo entiendo bien :)

[@cryalowicki]

I'd hoped you hadn't given up! Happy to see a new video!

[@johngraboski]

Bro, way to take it to whole new level! Continue, please and thank you o/

[@joechristman8721]

Awesome breakdown! Very well explained. Great job, thank you.

[@copypaiste]

Thank you for these videos, very informative!

[@nambrosino]

Extremely helpful video, great work!!

[@obi-wankenobi9871]

Thanks a million times for that video. I was searching for info like this for half a year.

[@lukeeames2003]

Nice video, I loved all your videos on rear suspension, can't wait to see what's next

[@davewalsh8278]

Great video, I learned something new. Thanks

[@emaildanielnow]

very well explained! great video, Andre. Keep it coming...

[@glikar1]

Thank you! Excellent explanation.

[@joshthet6598]

Thanks for your supreme work explaining these things to be understood easily and logically! You're a crack in this stuff. :-) Cheers from Austria!

[@moteandocongus]

Awsome material bro! Thanks

[@lejendpolevault5345]

BRILLIANT, Always look forward to your videos. Thank you!

[@andrextr]

+Lejend Pole Vault thanks :)

[@DRHODES1979]

Great video! Thanks for the excellent explanation.

[@hugojlsantos]

Top Top ! Obrigado Andre Tanks Andre

[@TylerBoothGolf]

Awesome stuff my friend! A few of my friends were asking about all this and a video is way better than me explaining it with nothing, so they enjoyed it too! Sub'd and can't wait to see more!

[@andrextr]

+The Tech Ring thank you :)

[@igehring]

Great video, it realy explains what I needed. Obrigado!

[@A80sM]

Great stuff, cheers mate.

[@andrextr]

Thanks 👍

[@stoenchu122]

I waited a lot for a new video!!!

[@SamoraksTechnicVehiclesYtube]

Feeling pretty happy with my Float X2 purchase right now :D

[@paulbalegend]

Samorak's Technic Vehicles as am I with my monarch plus debonair! but I already knew it was awesome :)

[@que_dijo]

amazingly well explained!

[@user-gb5rm5mu1y]

Andre, thanks for the video! please make more videos, particular ob the piggy back part :) thanks!

[@amhtxc2960]

Another awesome video.

[@andrextr]

Tks 👍

[@ThomasSchmitzSPFC]

Fala André! Você sabe do que você esta falando, e sabe explicar melhor ainda. Parabéns!

[@andrextr]

+Thomas Schmitz Obrigado Thomas! Um abraço

[@Josep_Barbera_Garcia]

Good job...

[@carlosadorno1544]

I'm tired of marketing reviews with subjective opinions and without substance where no quantitative information is included. Yours is a very good video! Maybe too technical for some but you explained very well as to make these complex concepts understandable for many! One question though: does your simulation consider a frictionless interface between chamber surfaces and seals? I believe that the absence of that "stiction" is one of the reasons why coil shocks are still a little more sensitive than air shocks. However, manufacturers have improved the surface treatment and seals as to reduce "stiction". Coil shock disadvantages are lack of progressivity tuneability, need for a specific coil spring rate for each rider weight/riding style, and weight (which I don't mind much).

[@andrextr]

+Carlos Adorno Hi. Thank you! Im also sick of biased and marketing reviews :) No, I'm not considering friction. Nor the temperature variations on the air under heavy use. But as you said, I dont think thats a major issue. Although I'm a coil-fan, an air shock with a proper negative chamber can be as good or better than a coil (less weigth and more tuneability). Bye

[@pandacharm]

Verry helpfull!

[@Phil-dg1yg]

excellent! big thanks!¨

[@gmc3578]

thank you! this is why I sold my linear bike!

[@useport80]

great video! can you do a video on how to setup rebound/hsc/lsc on forks?

[@EeroSoralahti]

Big thanks for this video! It was very informative. BTW: could you do some geometry / progressivity analysis on some full suspension XC-bikes? I would be interested to learn how they differ from e.g. trail bikes.

[@andrextr]

Usually XC bikes are linear or slightly progressive, and they have good anti-squats. The main difference is the amount of travel, and probably a bit less progressivity (which makes sense). I will try to give a look at this topic. Bye

[@MetroidChild]

What I gather from this is that a properly set up progressive coil (or bumpers) are probably similar to a properly set up air spring.

[@KubaCykloza]

9:30 When you've changed the volume of positive chamber, at the same time sag have schanged. Honestly you cant keep both the same as they were, sag and bottoming out force. If you deicde to get benefits from increased negative chember you have to be aware of those two things, you are going to get deeper into the sag or have higher bottoming out force. Anyway very cool excel and video, I would love to see charts with super deluxe with and without megneg

[@andrextr]

You can have big negative chamber and adjust pressure and increase main volume to get same sag and bottom out force.

[@KubaCykloza]

@@andrextr But at the end when I increase main chamber volume to get the same bottom out force the pressure will decrease. Pressure * volume is remains always constant in constant temperature.

[@KubaCykloza]

@@andrextr 9:01 you can clearly see that between different chart, there is force difference at 30% shock travel

[@Ghrostillo]

Yeeeesss!! New video :DDD

[@andrextr]

:D

[@Ghrostillo]

andrextr I have a question, what does all this stuff about travel on the manufacture's website like in this case fox stand for and what tells me the size of the negative chamber? There are just numbers without any explanation: Travel 7.875 x 2.00, 7.875 x 2.25, 8.50 x 2.50, 8.75 x 2.75, 9.50 x 3.00, 10.50 x 3.50 And what are typical values for negative chamber?

[@andrextr]

Brands don't share many details and data about their products (intellectual property), so it's hard to compare them. What I can tell you is that the EVOL sleeve, the Vorsprung Corset, or the Debonair have bigger negative chambers than the standard sleeves. However, it's not known how much volume they have. Accordingly to Vorsprung website, EVOL sleeve should be equivalent to the 10mm curve of my graphs, while Corset sleeve should be equivalent to 15mm. But I can't precisely confirm this info. Bye

[@Ghrostillo]

andrextr Thanks a lot! Last question, do you know anything about the Rockshox Monarch Plus RC3? Because I'm thinking about buying a YT Capra Al comp 1 and since the frame is super progressive it would be nice if the shock is quite linear at the beginning of the travel...

[@andrextr]

The progressivity of the frame is mostly obvious at the end of the travel. The monarch has 3 options, the Debonair, High volume sleeve (corresponding to the main chamber volume) and standard sleeve. It think the AL1 cames with the HV sleeve. Debonair makes the bike a bit more sensitive at the beginning. But the HV will also work well on Capra, and given the high volume of the main chamber, it will not ramp-up much at the end (since the frame is already progressive, you don't need much ramp-up on the shock)... I would say that Capra works well with any shock (eheh).

[@lux-3001]

Andre, what you are saying about bigger negative chamber only applies for light to average riders. For heavy riders, the big negative chamber means needing to pump in so much pressure, that the shock actually looses small bump sensitivity over a small volume chamber.

[@andrextr]

lux yes, it’s a balance between those two factors, and after a certain point there is no major benefit from having a bigger negative chamber, because the curve is already quite linear. Still, if you increase the diameter of the shock you decrease the pressure required without affecting the curve shape. So, manufacturers can play with that too. In episode 14 you can download a air shock simulator to play with those parameters. Cheers

[@lux-3001]

@@andrextr Hey, thank you very much for a detailed answer. You are a fountain of suspension wisdom! May I ask for a piece of advice? I went from a DebonAir air can to solo air air can on my Monarch RT3 190x51 as I couldn't set up my sag less then 35% at 350 psi on my nicolai g13 (I weigh 114 kg without gear). With the small air can, the shock feels very plush at the beginning and it ramps up at the end so I don't bottom out, which I like very much and the traction and small bump sensitivity is amazing, but the mid stroke feels a bit less supportive than I'd like it to feel. The damper has already been tuned by sram for my 114 kg body weight. Is there anything one can do to get some midstroke support? I ride a nicolai g13 which is quite progressive. Thanks for help if you happen to find time to reply. Cheers, Luka

[@nkitanov]

@@andrextr , thanks for your great work. I, am having the same problem, weight about 110 kg with gear. Have Canyon Strive 2016 with debonair monarch plus 200x57 and I noticed that I need to put crazy pressures to make sag 30% (35% with 300+ PSI, I don't even have a pump for more than 300). The previous owner put 4 bands and I didn't removed them, and even on 250PSI I ended up with 40% sag and couldn't able to shrink it to less than about 80%. So I am playing with your spreadsheet (although I don't have data for 200x57 but probably calculations are similar) and thinking about multiple options, taking into account that apparently debonair is not the best thing for heavy riders. 1. I think I need to remove all bands - still I have to put crazy pressure, but the shock will work better at the end as I can't use it's whole travel now with the steeper ramp up curve. 2. Going back to solo air can. I read a lot of heavy riders do that. 3. Putting bands in the negative chamber . I know that will change the curve at the beginning but still this will decrease the initial sag. 4. Is there any real need in making these 30%, what if I keep it 40% but the shock works fully. Yesterday I was riding and even decreased a pressure so I can have it better at the end... Not sure what really to do. Any advice is appreciated... Thanks.

[@andrextr]

Hi. The bands on positive chamber will only affect the last part of travel, use then only to reduce bottom out accordingly. If you put then on negative chamber you have a stiffer initial travel and it could help to reduce sag in your case (and you can use lower pressures). There is no need to make exactly 30% you can run 40% but it migth make the bike bob more. You have to test the different settings and see whats work best for you. Cheers

[@nkitanov]

@@andrextr thanks. I will remove the bands for now. The previous owner weight 65 kg, put 4 bands and 250 PSI for better mid stroke progressiveness according to his words. I find that odd to be honest but anyway. Will remove all bands, and add one in the negative and eventually play with decreasing the negative chamber. As you say, have to play a bit with the bands and pressure.

[@grantrogers1858]

Excited to see another video!! Question: You said modern air shocks have a negative air chamber length of 10-15mm which seems to be much better than previous designs. Why not make the negative chamber length 20-25? What effects would this have on the suspension and is it do-able, should it be done? Thanks!!

[@andrextr]

+Grant Rogers Hi. Thank you. Yes you can increase more the negative volume, however the more you increase the lower is the incremental improvement. But I believe in the future is to increase up to 30mm. The only problem is the lack of room to increase the length. However this is currently overcame by using secondary chambers (outer sleeve). This trick has the same effect as increasing the length. This week I will release a quick vídeo about this. I will also share my shock simulator to everyone, for free near Xmas... :D You can they play with numbers and see the result. Bye

[@FreakShowExcess10]

Can you talk about sealed atmospheric negative air chambers. Like what is found on the Manitou Mara Pro rear shock.

[@yas96225]

Love your videos and the insights. Could you do a suspension comparison across different disciplines (XC, Trail, Enduro, DH)? For example: How is the suspension of a Specialized Epic different from a Camber, Stumpjumper, Enduro or Demo? I just picked Specialized randomly to explain what I mean. I would be interested in how bike companies tackle the different objectives and the trade-offs they're making. Especially when going to the extreme of cross country, where pedaling efficiency is key.

[@andrextr]

I will try to do that on the future, it's an interesting idea and already got some requests on that topic. On my progressivity video I compared the progressivity of several enduro bikes with several DHs bikes. DH bikes have, on average, a progressivity of 40% while enduro bikes have 20% progressivity. Which makes sense, more aggressive riding requires more progressivity. For XC I guess that they have a low progressivity (between 0% - fully linear, and 20%). Regarding anti-squats (pedaling efficiency) almost all enduro bike have anti-squats close to 100% on a singlering setup. In XC bikes I strongly believe this is also true. On DH bikes the amount of anti-squats is highly variable. You have a group of DH bikes with very low anti-squats (eg: Spec. Demo), a group with ~100% (eg: YT Tues) and another group with very high anti-squats (Gambler)... So IMO, this somehow means that anti-squat is not very important on DH bikes, and you can go with low or high values (indeed, pedaling is not the most important on DH bike). Regarding the braking independency (anti-rise), I don't know if there are differences across the disciplines, but the anti-rise depends mainly on the suspension system, and not so much on the particular design. You can only get really low anti-rises (good brake independency) with an horst-link design. The singlepivots, or singlepivot with shock linkage or even dual-links designs (eg: VPP) can't get low anti-rise values (unless you use a floating brake arm, but that's rare nowadays). Bye

[@yas96225]

Thanks a lot. You're the man! I own a Specialized Enduro and was test-riding a Camber. I was surprised on how much better the Camber climbed. Sure, some benefits come from weight and tires, but I also felt that more power goes into acceleration vs. suspension. Seems like it's not so much a geometry thing, as the Enduro has a fairly low progressivity according to your videos. That means that I need a shock with a lower progressivity/bigger main air chamber to make my Enduro a better climber (but not an aggressive Enduro machine). I hope I got that all right.

[@andrextr]

All specializeds are linear or slightly progressives (incl. Demo). Camber and enduro have similar anti-squats, and similar progressivity (enduro has a bit more). Apart from tires and weight, Camber has 25% lower amount of travel. The more travel the bike has, the less efficient it will be for pedaling. This is the main difference between both. If your enduro's shock has a good pedaling platform, you can increase the pedaling efficiency by turning it on, on the climbs. Regarding your last question, the progressivity (of either shock or frame) affects mostly the ramp-up at the 2nd half of the travel, it won't affect significantly the pedaling efficiency. So, by using a bigger main chamber on your shock you are only increasing the amount of bottom-outs and not the pedaling efficiency... So, it not a good idea. YT Jeffsy 29er is a very progressive trail bike and I bet that it will pedal as well as the Camber. :) Bye

[@MrCirest]

thanks! btw i would be interested in an analysis of an orange five and it's single pivot.

[@andrextr]

+MrCirest Hi. Orange five has good pedaling efficiency (anti-squat around 100%), because main pivot height is the same as the top of the chaingring. In my anti-squat vídeo I used the orange example. The anti rise is around 90% as it happens with almost all single pivot bikes (see instant center episode). The progressivity of orange is low (its fully linear). Since singlepivot bikes dont have a shock linkage you can't get a progressive bike. The most you can get with a single pivot design is a very sligthly progressive suspension. I will discuss this in a future vídeo. Bye :)

[@MrCirest]

thanks for your answer!

[@tafit84]

That was very interessting. Thank you! Do you know which shocks have a big negative air chamber? Could you name some?

[@andrextr]

I listed them on the video... While I don't know exactly the volumes, examples of bigger negative chambers are Debonair sleeve, Vivid Air, Fox Evol sleeve and Vorsprung Corset sleeve.

[@alex098186]

Excellent videos!! You provide the most in depth and simple to understand explanation I have seen amongst others. I own and ride a cube hanzz with a float X rear shock and factory float 180rc2 up front. I have noticed the effects of your points on small negative chamber since I upgraded from the stock van rc coil shock. The float x does not have the evol air can but I am convinced to upgrade and looking forward to the improvement! I have the impression that my bike now has a linear or slightly regressive mid stroke. Can this also be due to the frame kinetics itself? it's got a 3:1 compression ratio, 190mm rear travel with 8.5x2.5 shock, horst link frame

[@andrextr]

Hi, thanks! Cube usually uses a very linear suspension in their bike models (sometimes even regressive, like the Fritzz 2011 !!). Your bike is no exception, since Hanzz got 10% progressivity... With the Evol sleeve (or the Vorsprung Corset) you will improve your shock performance, since you will double at least the negative volume. The float X has a small negative chamber, similar to the older fox shocks. According to this picture, it should have a negative length of 5 mm (www.mountainflyermagazine.com/img/upimages/2014_Fox_TalasFloatX/Fox_Tech_Float_X.png). Bye

[@alex098186]

Hello again! I purchased the Evol Air Sleeve and have already ridden my bike at local trails. While still using the same air pressure (200psi) I now have a higher percentage in sag setting, 30% compared to the previous 20%. I also changed the air volume spacer from 3rd to 4th (1 is smallest and 5 biggest). As expected, I noticed the softer initial travel, (better small bump compliance) but I'm still trying to figure out about mid stroke support? Maybe, I can feel a small improvement but not quite sure. The guys at Fox said that in order to obtain the full effect of the improvement, I need to send them the shock to reset the valving according to 2016 model standards. Any thoughts?

[@andrextr]

As I said, with bigger negative chamber, you also need more positive pressure to get the same SAG. To compare accurately the newer setup you must test it with the same SAG as the previous one. If you do so, maybe you can feel a firmer mid stroke when compared to the previous one. Not sure about the revalving... I don't think it's strictly necessary to revalve just because of the newer sleeve. I mean, the newer sleeve improves the shock, but it's not such a drastic change that requires revalving (factoryjackson.com/wp-content/uploads/2015/09/full_FOX_EVOL_Improvement_389053.jpg)... Did they said what was the point for the revalving? Probably to reduce the internal tune of mid/high compression damping since you got more support from the spring? (I don't know, I'm just guessing)... Bye

[@alex098186]

Thanks for your immediate reply! To be honest, all they said was that I will get better damping characteristics and more mid stroke support. Another thing noticed, is that "Climb mode" is not as effective as prior to Evol upgrade. Maybe this is why they insist on revalving? Other than that, I must mention that I noticed a good ramp up towards the end stroke and didn't achieve bottom outs, even though I tried hard to use all the suspension travel. The bottom line is that I gained traction and felt that i could overcome the mid stroke area by adding compression (turning switch to trail mode 1). I don't want to run 20% sag because this would make my bike feel too stiff. Overall happy but still have to figure out that mid stroke area. :)

[@andrextr]

The 20% SAG was just to test and compare with your previous result (since you said that you used to run 20% on older sleeve). Now you changed the sleeve and also the SAG, so what you feel is a mix of results from those 2 changes. With the newer sleeve and higher SAG, the initial travel will be much softer, so you won't notice so much the climb mode (probably in the revalving they also increase Lo-Speed Compression to compensate this). Have fun :) Bye

[@AlexUncut]

very interesting. is there more tweaking that can be done to achieve the affect of "big coil" shock like increasing psi level above recommended or using different gas (nitrogen/hydrogen) ?

[@andrextr]

Thanks. To make it similar to a coil, only by increasing the volume of negative chamber. Changing the gas or pressures won't result.

[@airtimecounts1280]

New Video

[@markcocjin]

Is the ideal curvature of progression the same across all types of mountainbiking? Is shock travel a good indicator of what a suspension is good for or is there a specific way a shock should compress depending on the usage? Another question is, can a 100mm travel xc bike frame be equipped with a different shock and be used for enduro? Is it a bad idea to replace a 120mm fork with a 140mm fork? Do front and rear suspension travel have to be the same or can you have longer travel on the fork compared to the rear? Should I just stick with the same travel a bike came with from the store? What is the maximum travel variation if ever?

[@andrextr]

The progressivity of the frame & bike will depend on how aggressive do you ride. For smooth and soft trails a more linear suspension will be better, since it will be easier to use all travel. For aggressive riding, with jumps and drops, a more progressive suspension will be better. The amount of travel is a good indicator for what the bike was designed for. It's not a good ideia to change the size of the rear shock since that can cause drastic geometry changes and clearance issues. You can increase the fork travel depending on the limit of the frame, which cames on the manual of the bike. Increasing 10mm, and in some cases 20mm, is not problematic, more than that is not recommended. Bye

[@marcowalther7867]

Hi Andre, thank you for this wonderful explanation! Though I don't have an engineer's mind, I get the point. My question is: I have the Kona Process 134 that comes with the standard small volume Monarch. The initial strong ramp up of the shock seems to counterbalance the bobbing under pedalling quite well, but I dont use more than 70% of the travel and the suspension is not very sublte either. Would mooving to a debonair shock run with slightly less sag make sense?

[@andrextr]

Yes, the initial ramp-up can be good for a more XC/Trail application (I have a mindset towards enduro/DH sometimes I forgot the pedalling part eheh). For those who want a more smooth ride debonair makes sense (the coil will be the best you can get). Regarding the 70%, are you sure about that? I'm asking this because there are some shocks where the ending of the stroke doesnt corresponds to the ending of the body (I'm not sure if that's the case, but you can remove the air to confirm or measure it). If everything is fine then you can increase the SAG in order to make it more softer and make full travel more often. How much SAG are you runing? Is the rebound tuned correctly (see the curb test on Ep.5). Try this first before considering the debonair. Bye

[@marcowalther7867]

I run about 28% of sag right now. And true, the shaft is 55mm long whereas the shock's travel is only 51mm. Like that I use only 80% of the travel. Maybe a little more sag will do the trick. After I had freeride and enduro bikes for the last ten years, maybe its time to enjoy the benefits of pedalling performance and let the Debonair pass. Thanks a lot for sharing your knowledge!

[@coronasean88]

fascinating stuff again andrex - I have a question, would increasing the negative piston surface area have the same effect as increasing the volume of the negative chamber?

[@andrextr]

+Sean R Good question. Short answer is no. Increasing diameter of negative chamber wont change spring curve shape, it will only decrease the pressures required on the negative chamber to counteract the main chamber. This is also true for the main chamber. The bigger the diameter of main chamber the lower the pressures required to get the same SAG. The reason why diameter doesn't affect the spring curve shape is because it also doesn't affect the compression ratio (the rate between inital volume and final volume is always the same independently of diameter). So only increasing the length will affect the curve shape. Since you dont have much room to increase a lot the length of the chambers, the alternative way is to connect the chamber to an external reservoir. Thats why manufacturers use secondary chambers outside the shock with a hole connecting to the primary ones. That is exactly the same as increasing the length of the chamber. Bye

[@LibertwinsBR]

ola amigo andre. qual programa vc utiliza para fazer essas mediçoes? saudacoes brasil

[@andrextr]

+gmcayres Olá. Neste vídeo utilizei um simulador construído por mim em Excel. Em breve irei partilhar com todos este simulador. Abrç

[@SneakyB]

hello, do shocks with smaller main chamber volume(such as fox CTD SV 7.25 x 1.75) benefit from having a bigger negative air chamber? Or only shocks with large volume benefit from a larger negative air chamber?

[@andrextr]

+sneakyb Every shock benefits from having a big negative chamber sleeve. As I said, bigger negative chamber makes the shock more sensitive and with more mid stroke support (les wallowing). The main chamber volume will only control the final ramp-up. Bye

[@tememma]

OK, so practically, how to change pressure in the negative chamber?

[@jay-rlacerona501]

hello sir,i want to ask if i can install air suspension in reverse position?which is the negative chamber is in the top and the main chamber is at the bottom? thankyou very much for the answers . . .

[@andrextr]

yes, you can flip the shock upside down, it doesnt matter (just check clearance if it doesn't hit the frame during compression)

[@shamusbip]

I know that pull shocks are very rare now, but how different are they compared to regular ones? I'm particularly curious of the equalizer from DT on the Scott. They do have pretty big negative and positive chambers​, almost equal.

[@andrextr]

Hi Razvan, yes that's rigth. I don't know much about the equalizer, but I did a model for the Dyad RT2 which should be kind of similar. And the negative chamber is around 3x bigger than a Debonair/EVOL sleeve and 6x bigger than a regular shock. This creates a very linear spring at the beggining travel, equal to a coil spring. The disadvantage of this, is that you need to use very high pressures on the positive chamber to achieve a normal SAG. As a consequence, the main chamber also needs to be big otherwise the increase in pressure at bottom-out would be huge. This makes the Dyad RT2 very linear in the whole travel. The equalizer shoud be similar I guess. The only way to increase the negative volume without using too much pressure on the main chamber is to increase also the main piston diameter. You can check the Dyad RT2 model in my free air spring simulator here: kzbin.info/www/bejne/Zl7PY59ooMiUZqM

[@shamusbip]

andrextr I have this link ( assets.scott-sports.com.s3.amazonaws.com/suspension_setup_tool/index.html ) from Scott, who shows different curves of the shock. I was wondering if you increase the positive air chamber above the recommended values, will you get more progression at the end ?

[@hclee6103]

Rockshox generally has a firmer feel at initial stroke than fox does. So does that means Rockshox has smaller negative spring? Or is it the compression damping making the difference? Tks ==

[@andrextr]

I don't know which shocks do you compared, nor if they had the same settings and base tunes (L,M or H), but it can be both options you mentioned. I also don't know the exact negative volume of Evol (no diagrams or cross-sectional pics available), it might be different compared to Debonair / Vivid air, but my guess is that they are comparable. Bye

[@R1Gato]

Could you talk about what top out means? I think you’re referring to the position where the equalization notch is, but the naming isn’t quite common sense. Where in the stroke (ie what percent of travel) do manufacturers typically put this notch?

[@andrextr]

Hi. Top out means fully extended. I dont know in which % manufacturers place the notch, but if made correctly they should place it exactly where the resulting equilibrium pressures will produce an equal force on both sides of the piston (and thus, the forces will cancel out each other to make a sensible initial travel).

[@R1Gato]

@@andrextr thanks, I’m realizing the top out question was a stupid one. It as for the notch, when the piston crosses that travel point then the pressures on each side are exactly equal, which brings several questions. First, if the pressures are equal, then shouldn’t the forces be also? If they are, then what is supporting the rider? The net force can’t be zero, so this suggests the piston areas are different between the positive and negative sides. Next is where manufacturers choose to put this relative to the suggested sag point of the shock (which is also bike specific). This brings a big but subtle point in that perhaps a riders preference of sag could be driven not just by all the complexities of bike geometry but also by the location of the sag point in the spring curve relative to the shape of it, which is largely driven by the axial travel location of that notch.

[@andrextr]

@@R1Gato yes, the surface area of the piston is different, so in order to have a net zero force balance, the negative pressure needs to be higher at the top-out. In that way you eliminate the initial breakaway force and you have a supple initial travel. If the notch is placed correctly you achieve this balance independently of SAG and pressure used. And if the notch is placed too downstream, you end with a partially stuck down shock (it won't fully extend). If you place it too upstream it fully extends but it has that initial breakway force. I have more videos about this topic (Ep 13.5 and Ep.14)

[@MTBScotland]

the spring curves don't take into account the drag caused by air seals though do they?

[@andrextr]

+MTB Scotland No it doesn't, however those forces are quite small when comparing to the forces from the spring. Also, the air spring curve doesn't take into account the forces of oil damping (compression damping), because those forces are dynamic by nature and depend on how fast the shock is compressing. So it's impossible to represent them on these force vs position graph. Bye

[@dtran1742]

Hi, i have a 2019 nukeproof mega 275(230x65 stroke) with a meg neg. Im at 0 positive bands and 3 negative bands using about 6-70% travel at 30% sag( 250psi, 90kg). if i understand correctly, if i was to have 0 positive and 0 negative bands at 30% sag i would use even less travel since there will be more force to bottom out. Would i then need to increase my sag to 32-35% sag,increase to 4 negative bands for more travel use ?

[@andrextr]

Yes, more negatives bands reduce the air pressure required to achieve the SAG, so it will indirectly reduce the bottom-out force. But you lose some of the initial sensitivity and the propose of having a big negative volume :) Nukeproof has a progressive linkage, but from what I remember it is not excessively progressive so I assume it would be relatively easy to use almost all travel at least on some mid-sized jumps and drops. Best

[@dtran1742]

@@andrextr i'll remove the negative bands again and try my testing again from 0 positive and 0 negative. thanks for responding!

[@patrikprielozny3256]

What's your opininon on the RockShox Megneg for Super Deluxe? I'm considering that for Nukeproof Mega 2020 275. Currently running 2 tokens and bottoming out only on casing jumps so I guess it could be a good fit.

[@andrextr]

I think MegNeg is a great upgrade to an air shock because of the reasons explained in this 2016 video. It gives you a very coil-like feeling with the possibility to still tune bottom out resistance with spacers. Actually rockshox provides good tech info about this product. Give a look on theirs product datasheet. NP Mega has a progressive linkage by the way. Cheers

[@patrikprielozny3256]

@@andrextr thanks for the reply! NP Mega has like 0.5 LR difference, which is slightly progressive as I can see - I actually can't find info on 2019-2020 models, but historically they always went around 0.5 diff (2.4-2.6-2.1). Ad MegNeg - yes it seems to make sense. I have checked the info and some user reviews on forums. I was just wondering why whouldn't rock shox just increase the negative volume more on their stock shocks, but I guess it comes with the penalty of needing to run higher pressures and then people already running over 250psi would need to run over the max (325 in Super Deluxe). So I guess it's good evolutionary option to give the tunability and expect that this tuneable chamber will become available on stock shocks in future, maybe increasing the range of tunability so that heavier riders can just leave all spacers in to achieve current stock volume (instead of ~160% with all spacers with Megneg). For me it makes sense that MegNeg is for lighter/medium riders with already some tokens in positive chamber, for which I might qualify (70kg, 2 tokens in stock can).

[@andrextr]

@@patrikprielozny3256 Yes the penalty is that it limits the number of customers (heavy ones). Probably in the future they would also increase shock diameter to decrease overall pressure... Regarding Mega LR, more importantly than the magnitude of LR difference is the way it changes (curve shape). Most of the LR decrease occurs in the second part of the travel (very steep LR curve slope), so this maximizes a lot the overall progression. For instance on some Evil delta bikes the LR decreases a lot in the begining then the curve becames flat in the second half of travel (this results in low overall progression). So, calculating the progression based only in LR difference does not tell you almost nothing! :) Cheers.

[@patrikprielozny3256]

@@andrextr huh, didn't know about that. Just comparing to something like YT capra it didn't seem that progresive. Lately I read the other thing to consider is rebound range, as more neg volume will slow things down so you should have some reserve. Strangely out of all sources I only found this on one german forum.

[@d.l.918]

So, if I'm fine with my bike's small bump compliance and progressivity upgrading to an EVOL or Corset is not really worth it or am I getting this wrong? Though if I also adjust the positive air chamber (less volume) it would make me use less travel most of the time (before bottoming out) and thus preserve geometry. Then again if it is a steep geometry that may not be good either.

[@andrextr]

These sleeves will increase by around 20-30% the sensitivity of the shock under SAG, while the mid travel gets firmer, reducing excessive mid travel wallowing. So the bike stays a bit higher on the travel. The volume of the positive chamber will mostly affect the final part of the travel. The ideal is to use all the travel on your normal rides without feeling too many harsh bottom-outs, and that can be controlled by the amount of spacers on the main chamber. If you want to improve your shock performance, then this is a good update to consider. Bye :)

[@d.l.918]

andrextr forgot to say: thank you for your advice. It's appreciated.

[@d.l.918]

Hey Andre! One thing has been puzzling me: What effect does installing offset bushings (those that effectively reduce your shock's eye-to-eye length) on the bike's suspension? As a layman I would assume that it would "move the spring curve to the left" slightly as with the shock fully extended the kinematics are now in a position they would normally have when the shock is slightly compressed. Is this correct? If so, while I realize the effect will not be much, it could still mess up the suspension, for example if it is designed to be degressive only for the first milimetres of travel and then ramps up. Potentially (with sag) the offset bushings will eliminate or at least significantly reduce the degressive part making the suspension a lot stiffer, no? Or am I thinking in the wrong direction? EDIT: To clarify, I mean offset bushings like these: www.offsetbushings.com/pages/how-they-work

[@andrextr]

Hi. Yes, it will shift a bit the leverage curve since with bushings the 0mm starts now in the older "5-10mm" point and the 160mm will correspond to a 165-170mm on the older bike (the values are just an example)... The initial shape of the leverage ratio does not have a major effect on the final result. Only the final shape of the LR curve has a significative effect on the final result. If the final part of the LR has something crazy with it (like it becames suddently very regressive), with these spacers you are moving further in that crazy part of the LR. In some cases you might also get some clearence issues (rear triangle hitting the seat tube). There are also other special cases on dual-links systems (like this chinese bike: www.yishunbike.com/mtb_frames-89-27-5er-full-suspension-am-enduro-carbon-frame-lcfs705-lcfs705), in which if you put those spacer you will not be able to get full travel (see this ugly animation explaining why: kzbin.info/www/bejne/jGrSgmifid6Yqdk ). But overall the offset bushings don't have any problem and don't affect much the suspension, only in a couple cases can be more problematic. Bye

[@d.l.918]

Thank you very much for this clarification!

[@nicoofner85]

+andrextr What can you say about the NS Bikes Snabb E? What is your opinion?

[@andrextr]

It has a well designed suspension. Good pedalling efficiency (Anti-squats of 100-120%), it's quite neutral to braking (anti-rise 50%) and it's slightly progressive (progressivity of 25%). Bye

[@nicoofner85]

andrextr Thank you! I noticed that it is not very progressive....I use a lot of volume spacers in my debon air shock. This video really helped me to understand airshocks.

[@andrextr]

On average, enduro bikes are not very progressive (most of them have 20-25% frame progressivity). IMO, Enduro bikes should have 40-50% progressivity. Anyway, if you have a debonair with max spacers there is not much you can still do to improve the bottom-outs... You have to live with that :D Bye

[@paulbalegend]

Nico Ofner you can pump it up, that'll increase bottom out resistance! :)

[@massimilianodelise1505]

I wrote this article some time ago. It's in Italian because I'm Italian, but the graphics will understand them www.mtb-mag.com/guida-sul-funzionamento-degli-ammo-ad-aria-e-loro-set-up/

[@andrextr]

Thanks for sharing! I can recognize right away some of your graphs with those in the video :D I will give a look for your article with the help of google translator :) Bye

[@andrextr]

Gave a better look for it, google translator didn't make a good job, but I understood some parts... some of them are similar to the ones in this video. Just a small commentary on your Fig.4 (not sure if I misunderstand it but...), the transfer port between both chambers is located above the piston at top out. This is because the contact surface area with the piston is smaller on the negative chamber side (see my shock diagram in the video), therefore, negative chamber requires more pressure than the positive in order to produce the same force as the positive chamber. BTW, nice work! Also briefly looked to your other article (Hydraulics part 1), it seems pretty nice, already saved the link on the favorites to read later :) Bye

[@NitzanPapir]

what does the piggy backwhat does the piggyback gives you in those shocks then?

[@user-gb5rm5mu1y]

I believe they keep the oil under sufficient pressure to not let the oil get vaporized by the low pressure while decompressing..

[@andrextr]

The piggyback contains an air chamber (IFP) that is required to pressurize the oil (inline shocks and coil shocks also have that chamber). The IFP contribution to the spring is not very important, but it shifts the curve up like in this pic: ep1.pinkbike.org/p4pb14201762/p4pb14201762.jpg . The IFP contribution was discussed previously in this video: kzbin.info/www/bejne/f6qraZuEgddko5I