IFP forces on rear shock (MTB rear suspension Ep.9)

[@maximilianlindner]

Your videos are so awesome!!!

[@andrextr]

+Max Lindner thanks man :)

[@Balotca]

Well explained, sir :) I'm writing my uni thesis about mtb's rear suspension kinematics, your channel just comes in handy. Keep on with those videos! Cheers!

[@andrextr]

+Igor Žerjal Nice :) Enjoy! Bye

[@seanharanmtb7923]

Another great video!

[@HannyDart]

every mountainbiker should watch this series :D

[@andrextr]

+BAEMERZ Thank you man! Share it with your friends ;) Bye

[@garybrown5769]

They never suggest changing IFP pressure for fine tuning, i have a superdelux ultimate, runns 250psi in the ifp, dropping to 200psi or 175psi makes huge difference in small bump. and actually improves the "drop test"..... endless tuning with air

[@jbs3691]

Hi Gary. Did you have any longer term negative results from dropping the ifp pressure in the super deluxe ultimate to 175psi? Any air getting into your damper?

[@TheEthalon]

This video is perfect. Practical examples, math and comparison.. liked and favourited

[@andrextr]

The Ethalon thanks👍

[@jeromeahn1384]

Thank you for the awesome videos! I have a question about IFP. In the video, IFP pressure is only shared around 10% of compression and rebound forces in a shock. But makers strongly recommend following their instruction about IFP depth. Please explain why this is critical. And one more, how to calculate IFP depth. Some shocks such as Fox Dyad RT2 from Cannondale can't find the IFP depth information.

[@andrextr]

Hi Jerome. IFP is used to pressurize the oil. As the shock compresses and the shaft enters into the shock body it will displace oil (because shaft occupies space). The IFP then compresses to accommodated this oil displacement. As the IFP piston moves the gas pressure in the IFP chamber increases. If you start with a low IFP height then you get extreme pressures peaks at bottom-out and you can destroy quickly the orings or the shock. This is why you should respect the IFP height when bleeding the shock.

[@ontheway7335]

How much pressure can i put in my ifp??

[@TheJosesilva69]

Big hit 3 M4?

[@andrextr]

Yes my “DH” bike :)

[@justing6614]

Hi Just a quick question would I be able to safely add 5-10% more pressure in the IFP chamber to get slightly better bottom out resistance in my rockshox coil shock?

[@andrextr]

Better use a stiffer bottom out bumper or a progressive coil spring (not sure about internal diameter compatibility with rockshox shocks)

[@grantwarden7848]

Andre, this description of breakaway, commonly known as static friction or stiction, is just plain wrong. What you're measuring is preload due to IFP pressurization - not the force required to make the shock start moving from a stop at a given point in the travel, which is the actual breakaway force. That's why you got similar results for air springs and coil springs.

[@natanaellorenzi5]

Olá Andre... Meu shock monarch Plus RC3 na Minha nomad quando eu solto, não acenta no chão como a tua bicicleta com esse shock. Ela fica a pular como tua bicicleta sem shock, e isso independe dos ajustes feitos no shock. Cumprimentos do Brasil! 🤟🏼🤟🏼🤟🏼

[@MilkBone3327]

Thanks for knowledge! I'm curious on your thought of Trek's new thru-shaft. Which I believes eliminates the IFP. Do you think we could see more bikes going to this technology? Thanks

[@frutkick]

MilkBone3327 it looks like riockshox deluxe rear shock still has IFP. But it is small

[@andrextr]

+frutkick The newer RS shocks have a spring above oil piston to eliminate or reduce ifp-induced breakaway

[@ronnevh2788]

kkk tenho uma balaça igual ah tua.... acho que tambem devias ter os videos em pportugues

[@andrextr]

pois mas isso dá muito trabalho :D kkk abrço

[@natanaellorenzi5]

@@andrextr Olá Andre... Meu shock monarch Plus RC3 em Minha Santa Cruz Nomad quando eu solto, não acenta no chão como a tua bicicleta com esse shock fox que estás a usar. Ela fica a pular como tua bicicleta sem shock, e isso independe dos ajustes feitos no shock. Cumprimentos do Brasil! 🤟🏼🤟🏼🤟🏼

[@andrextr]

Ola. Quantas voltas de pre-carga? (Preload?). No máximo 2 voltas. Se não resultar, quando pressiona no selim (saddle) só com um dedo (polegar, thumb) o shock começa a comprimir? Ou é preciso pressionar o selim com a mão inteira?

[@natanaellorenzi5]

@@andrextr É um shock a ar e está com Sag de 30%. E não, não consigo comprimi-lo só com o dedo, preciso fazer uma grande força. Um colega usa um Fox DPX2 e o comportamento é igual ao teu de mola. Será que esse Monarch é muito ruim?

[@andrextr]

Ok então se é preciso muita força para vencer a resistência inicial e começar a comprimir então temos 2 hipoteses: ou existe fricção excessiva nos rolamentos do triângulo traseiro ou nos olhais do amortecedor / ou o próprio amortecedor tem muita resistência inicial (breakaway), tenho um video que explica isso (ep13 air spring curve , penso eu).... experimenta tirar o ar todo e vê se a suspensão traseira mexe sem nenhum atrito (para excluir a primeira hipotese)

[@blackielude9145]

Thank you for the in-depth explanation of what the IFP on a "piggy-back" coil shock does. This is very helpful, since I was having a hard time figuring out if changing the IFP pressure would affect my coil shock performance (Rockshox Super Deluxe Coil). I will now tweak the pressure some to see if I notice the end of stroke effect changing at all.

[@darkomtc]

Hello. Will higher IFP pressure increase the ramp up on air shock? I have "high volume" RP23 which is really linear since the volume is huge and I want to make it more progressive. I've reduced the volume with spacers, but did higher IFP even do anything?

[@andrextr]

Yes it would increase a bit the progression but also it reduces the sensibility (by introducing more breakaway force). Best way is to reduce volume of air spring (or reduce IFP chamber volume also...like the old DHX5)

[@darkomtc]

@@andrextr Thank you very much!

[@TeamCykelhold]

DVO and x-fusion uses a bladder to counteract the IFP stiction. Works well enough.

[@darkomtc]

Hey! 5:49 You said that Force = Area * Pressure which is okay, but shouldn't area be the piston area that compresses the gas in IFP chamber and NOT the shaft cross section area?

[@andrextr]

Its the cross section area. Because the oil side is also pressurized and the net result is the cross section area.

[@darkomtc]

@@andrextr and yes, this makes sense, both sides pressurized, and only cross section of shaft is left! Thanks

[@ryanbrown6756]

Very helpful video, also this man sounds like gru

[@guamandjiujitsu671]

your videos are so awesome. thanks @andrextr

[@andrextr]

+yutarosan calip Thank you! :)

[@andrextr]

+yutarosan calip By the way, interesting cardiopulmunary playlist on your channel, I will give a look for it ;)

[@guamandjiujitsu671]

+andrextr haha thank you. i am a cardiopulmonary instructor in the USAF. So when im not riding, im teaching students how to save lives! Keep up the great work man!

[@BanZ080484]

Hey thanks for all your videos - i have learned a lot... :) As for you it is a hobby for me to understand the mechanics MTB and the suspension system - but i like to learn more.. I have a university degree in math and a background as an electronic technician so I like to finde some more in-depth knowledge of the subject.. Do You have any good .pdf, videos, books or somethings that have more on the subject..? And Also... Do you work for weride.pt... as a guide or something? In november I went to Sintra and hade Hugo as a guide for some days - I will try to go back next month... VH Jesper From Denmark.. :)

[@andrextr]

Hi Jesper, thank you for your message !! I did some jobs for WeRide as a guide and mainly as a driver. They are old friends :) I used to do DH on Sintra, but lately I'm not riding much. Regarding the videos, there are many sites on the internet but the info is somehow dispersed. I also found a lot of nice things on MX or car suspensions that can be translated to MTB. You can check the linkage design blog from Antonio Osuna or the Tuesday tune of Vorsprung suspension (pinkbike) for more info. There are some books about kinematics, the most important is the "motorcycle handling and chassis design" from Tony Foale. If you have a more specific question we can discuss that. I have more ideas for future videos, stay tuned. Bye

[@randommtbing5631]

Cane Creek uses a 8mm shaft (excluding some Specialized models). Wouldn't that result in lower break away force of the shock? Were there results of cane creek shocks send to you? Thanks for great channel!

[@andrextr]

Hi Jarno. Yes, a small shaft decreases IFP-induced breakway because the breakaway force is equal to cross sectional shaft area X IFP pressure. I built a shock simulator (EP14, free download) where you can input those values and see the effect. The problem of small shafts is the durability... kzbin.info/www/bejne/Zl7PY59ooMiUZqM

[@rodolfohp8251]

you are a master explaining, in conclussion you recommend me an air shock with ifp or air shock withot ifp

[@andrextr]

99% of the shocks have an IFP (you need it to pressurize the oil, otherwise it won't work as well). The only exception is DVO shocks which use a bladder to pressurize the oil instead of a IFP piston. Rockshox has the "countermeasure" technology in some shocks which reduces the initial breakaway force of IFP increasing the sensitivity (it is basically a negative spring). Cheers

[@dmitrimoudraninets7761]

You forgot to mention friction.

[@SaettaJ]

Hi, congratulations on your video. One question: but if I didn't have the manual with the ifp depth and pressure indicated, is there a way to calculate this measurement and the contrast pressure?

[@andrextr]

Yes, just calculate the volume of shaft that will enter inside shock body and displace the same volume of oil. The final IFP chamber volume will be equal to initial one minus shaft volume. You then can calculate pressures and ifp heigth 👍

[@SaettaJ]

@@andrextr Thanks, can you give me a practical calculation example? For me it is not that easy, you are very good at these things and very fast, I need to calmly understand the calculations to be done. Thanks for your very kind time

[@ferodoracing]

@@andrextr Hi Andre , I m also interested in a pratical example to better undestand teh calcutaion. How do you calcolate the pressure ? an easy example please

[@andrextr]

Although calculations are simple, there are some steps and formulas involved to explain them on a KZbin comment… drop me a formal request on my website, I can make an excel spreadsheet to calculate all you want. Thanks

[@SaettaJ]

@@andrextr Thanks, i wrote you !

[@RxMTB]

Ohhh, a surprise!

[@vvtt1823]

Awesome video on IFP! Does the Fox X2 or Ohlins have IFP chambers have high pressure as well?

[@andrextr]

+Vasil Tashev Ohlins uses a bladder instead of a ifp. Dont know about X2 IFP pressure but the brakeaway results also include some X2 shocks and they are not much lower than the others.

[@vvtt1823]

+andrextr Thanks What I was asking basically was does the X2 extra chamber actually IFP as well?

[@jack91522]

Do you feel its important to use nitrogen?

[@andrextr]

Hi. It's always best to use nitrogen but I don't think there is a big difference comparing to normal air. In many shocks with adjustable IFP pressure (eg: DHX...) you end up using just air and it works just fine.

[@עמיתיפרח-ה5ס]

Hi! I didn't undestand.. the shock in the video have 3 forces that react against the compressing force produced by jumps or bumps you said that: 1. force of the spring (air or metal spring). 2. is the "chims" and other internal components, that affect the break away force (because they are not "ideal" components that have zero fraction etc?) 3. the force of the IFP. so, why would I need an IFP? the spring can be denser (air or metal) why do I need the IFP for?

[@andrextr]

The IFP is required to pressurize the oil of the damper. The oil in the damper is responsible for the compression forces and rebound forces (point 2). For instance, the damper slows down the rebound speed by forcing the oil to pass on small orifices and shims... and by turning the rebound knob you are changing the size of the hole, and therefore, you are changing the damping by changing the oil flow resistance. The damper can also control the compression motion, by the same mechanism. For instance, if you have a lot of compression damping, it would be harder to bottom-out (but the ride quality became stiffer and harsher). A shock lock-out is the extreme case of compression damping (where the oil circuit is fully blocked, and therefore the shock is locked out). So, why do you need an IFP? Because without IFP the pressures in the oil can get very low during shock movements, and the oil gets foamy and cavitates (vapour bubbles), and the damping became inconsistent and the shock life is reduced (kzbin.info/www/bejne/hJPMeXyvhJ15e7s).

[@עמיתיפרח-ה5ס]

thanks! can you please write where can I read good articles or watch good videos that explain about MTB shocks specifically? the video you linked I belive from a car channel. and generally where can I learn more about the MTB stuff from frame to shocks? thanks! please keep making there videos, they help a lot!

[@andrextr]

You can find some basic concepts in this rockshox guide: www.sram.com.cn/sites/default/files/techdocs/rockshox_suspension_theory_10-replica.pdf There's no much deep info/data about particular mtb shocks on the internet. Manufacturers don't disclose much details. Usually what you find is biased marketing claims. Bye

[@drierdan]

I just did a simple air can service. When I put it back together , and sat on the bike it went all the way though the travel. (100% sag) I put in 182 PSI, and it held air. Even after it went through the travel, it still had all the PSI. I checked everything inside, and nothing stands out. My only clue is that I dropped it on the ground while working on it. Could I possibly have lost pressure in the IFP? I took the cover off the IFP valve and air popped out. I then checked the IFP pressure and it was at 250 PSI (well below the 500 psi) on the SRAM website. I opened up the piston, put in new oil, and reset the IFP thingy. I then put in 300 psi (my max on my pump). No change I really don't want to take this to the shop. I fell like it's something I'm missing Any advice?

[@andrextr]

Does the shock gets stuck down after compression or does it extends back to normal? It seams the air is passing through the main piston to the negative chamber during compression and then it goes back to main chamber during extension. Check the main air seal (did you forget to put it back?) and check if the air can is not deformed. You need to have a good sealing between main piston and air sleeve during all travel, otherwise the air passes through making the symptoms you describe. PS: its not the IFP

[@andrextr]

If you didn’t understand my point check this video and see diagram at 2:30 kzbin.info/www/bejne/aXnIfWiEg62VfNk

[@drierdan]

@@andrextr thanks for the reply. I did not take the seals off. And it was working fine before.. Add more grease? Can't figure out what changed. Should I just give in and take it to the shop? Ps I have a thread going on MTBR in the suspension section

[@drierdan]

@@andrextr also, it does not get stuck down. Works like normal. I added way more psi, just to see, and that stopped the blow through but felt really odd

[@andrextr]

Its hard to diagnose the problem by the internet without seeing it, but I still mantain my opinion given your description... probably you need to send it for a technician 👍 cheers

[@ClimberGuy1]

With the deviation between air and coil shocks IFP pressures being negligible: why, then, in the drop test(in your other video) do they produce such drastically different results? Shouldn't the "negative pressure" companies are using in air springs create a similar effect in breakaway force? Also, i have a Mission Pro 2016, and would love to see an analysis of the suspension as you have shown for many other models. What software are you using to run these simulations? Loved your videos man. The scientific/statistical approach to analyzing different suspensions is very enlightening! Appreciate your hard work!!

[@andrextr]

+Bennett Dahl Hi man thank you! In my next episode I will talk deeply about the negative chambers, and how their volume affect the air spring curve. After that I will talk about drop-test. In fact, the other video of drop test is almost 7 years old, and I used the air shock that came on Enduro SL (AFR shock). That shock lacks the transfer port that pressurizes the negative chamber. Thus, the breakaway force on that shock was about 40kg (at least twice the value of a modern shock). On the AFR, the shock didn't even compressed with the drop-test. On modern shocks they still compress (you can use the o-ring to check), however, and that's the interesting part that I was not able to understand for a long time, in most modern air shock the wheel still bounces despite the low breakaway force. The reason is due to the higher low-speed compression damping. Indeed, I have some slow-motion footage that shows clearly that. The shock compresses during the impact, but then, when the shock it's coming to a stop it suddenly stiffens (semi- lockout), and the wheel bounces. I will discuss this in a future video :) Bye PS: added your bike to the request list :)

[@aptivaasdf]

+andrextr I was under the impression that the negative chamber in modern air shocks is not charged until the shock is sagged due to the positioning of the transfer port. Perhaps an air shock with independently adjustable positive and negative chambers (ex Rockshox Dual Air - not Dual Position Air) would show comparable results to a coil since the negative chamber is pressurized at rest? www.pinkbike.com/news/Tech-Tuesday-negative-spring-air-shocks-2012.html

[@andrextr]

The transfer port is above the main piston when the shock is fully extended, thus, each time that the air piston passes on that zone, the both chambers are equalized. This is what happens when you fill the shock for the first time for instance. After the negative chamber is properly pressurize it will remain pressurized. So the transfer port is an automatic way to properly pressurize the chamber. The height of transfer port determines the pressure of the negative chamber. To achieve a full equilibrium at top-out between positive and negative chambers, the negative pressure must be higher than the positive one (because the negative chamber has less surface area on the main piston, due to the space occupied with the shock body). I will try to do this episode this month. Bye

[@aptivaasdf]

I see. Thanks for the explanation!

[@TheEthalon]

8:50... kg and Lbs mixed up a little bit

[@andrextr]

The Ethalon Hi! Didn’t find any error at 8:50... If I remember correctly the only Lbs values used are for spring rate since its the default unit on Mountain bike springs. Cheers

[@TheEthalon]

andrextr ahhh I understand!! Thank you, amazing video

[@chris7605]

It's a very amateurish video and poor explanation. You try to be the engineer here: you call the IFP the nitrogen chamber. IFP is the piston (Internal Float Piston) or Separator. Then you talk about the unsprung weight. The UW the way you weight it is totally wrong. When you move the position of the frame with your hand, you can see that the weight (of the wheel with the balance and so) can vary. So how do you determine the position to put your frame in order to get the UW ? So for a start, your "breakaway force" is wrong. Then, the force that is produced inside the shock by the Nitrogen, produce of course a resistance for the movement ... you calculated or measured 18 kg to compress the shock, like 50 mm ? right ? then the force is a great fraction of the sum of spring force and the damping. The idea of the IFP force or the nitrogen is not to add some resistance to compression. Some suspension have less pression other more ... there is not way that the Rf due to the nitrogen is 20 or 25% of the total force of compression.There is also no way you can compress the shock with the spring installed manually !!!! To measure with accuracy you must use an expensive shock dyno ... when you know to use this tool, you know you perform a prior main test to measure the internal forces + force du to nitrogen to remove it from the equation (because what you look for using a dyno, is the effect of the damping), you can see that this is about 2 to 5% from the spring. I am very disappointed.

[@andrextr]

Hello my friend! I don't understand why so much hate from you, but OK.... The video is amateurish because I did this as a hobby and not as a job (channel's description). You are trying to be very picky with small details... For instance, it's obvious that the IFP itself is the piston and not the whole chamber.... but it's implicit than when you talk about IFP pressure you are talking about the chamber, which is known by many people as the nitrogen chamber... So I don't know where is your doubt! Regarding the other questions, most of them I didn't understand exactly what was the question... I believe you misunderstood many parts of the video, like the part of "you calculated or measured 18 kg to compress the shock, like 50 mm ?", where did you get the 50mm from??? That force value was the minimum force required to start compressing the shock (maybe 2-3 mm), and the value was obtained by two approaches: using the scale (real experiment) and by a simple theoretic calculations using the F=pressure/area formula.... And yes, the IFP pressure can easily account for more than 10% of total shock compression as I just show in the video, with a real experiment (of course that the final contribution value will depend on the IFP pressure and the main spring strength... here I just showed one "normal" example)!! If you don't believe it try to do your own experiment. Or use the simple math formula F=P/A .... Regarding the unsprung weight question, I don't understand why you said it's wrong, and didn't understand well this part: "So how do you determine the position to put your frame in order to get the UW? "... You can hold the frame it in any position, providing that the main frame is suspended by your hand... the scale wont move almost nothing because the weight on top of the scale comes from the wheel/rear triangle... And the value in my case is 5kg which makes total sense (QUICK calculations: 1.2kg of tire + 500 gr tube + ~1.6kg the wheel & cassete + the rear triangle & brakes which should account for more +/- 1.5 kg.... so, a total of 5kg ). You can try to do that experiment !! If you don't believe, just dismount the rear triangle and weight the pieces separately..... PS: Are you from Brasil ? Se sim, podemos falar em português. Bye and sorry if the answer was to harsh... We can discuss this openly without any problem. Bye