Dirt Bike Suspension vs Chassis EP. 3 | Understanding Fork Oil Volumes

[@jetrep]

Great visual. Thanks for making this video. I think it's worth pointing out that the perch would start seeing oil at a higher level than what you displayed. As the outer portion of the cartridge compresses it enters the oil which will increase the oil level height pretty quickly. The spring being compressed will also increase the oil height.

[@RideJBI]

You are spot on! That is an excellent point to mention and clarify.

[@tcparker2]

I really like this series. And appreciate the visual aid to really help me understand what’s going on inside forks. 👍🏻

[@RideJBI]

You are welcome. Thank you for tuning in. More to come.

[@robwhiting1924]

Brilliant, you guys are really helping me out now. I can offer JBI stuff to the guys in the UK.

[@coldsteeloffroad]

It's good to see some MTB suspension technology crossing over into the moto world via your volume reducers. I could be wrong, but I'm not aware of any other company that does this. This fact and videos like this one are good examples of reasons why I decided to have you tune the forks on my '25 CRF450R... I can tell you're passionate about this stuff & know what you're doing. One thing worth mentioning for the layperson regarding volume reducers is that while the entire travel is effected to some degree throughout the stroke, the main effect is in the latter part of the travel so they're used as an additional device to further control bottoming resistance. Keep the vids coming! 🤙🏻

[@RideJBI]

Thank you! The MTB suspension is the inspiration for the volume spacers. MTB suspension has really cool features, components and designs.

[@coldsteeloffroad]

@@RideJBI agreed. Would be really cool to see adjustable bottoming control via external adjusters incorporated at some point like on some of the coil shocks and forks. Do you ever watch ol' Steve from Vorsprung on KZbin? Bet y'all would get along 😂

[@RideJBI]

Agreed. It would be really cool. I’m not familiar with the channel. I’ll check it out.

[@jeremyrobinson4064]

JB FANTASTIC VIDEO SHOWING THE DYNAMICS OF OIL VOLUME EFFECTS ON FORK ACTION WITH VISUAL EXPLANATION ❤

[@ryantaft_411]

Phenominal video, thanks for doing this! Great explanation, fun stuff to listen to. Definitely going to go watch the other videos in this series and probably order some parts!

[@RideJBI]

Hey Ryan! Thanks for tuning in and expressing your interest in JBI Parts. Episode 4 of Suspension vs Chassis coming soon! If you have any questions on JBI Parts or Services don't hesitate to call us at 480-269-5585

[@strifex-suspension-works]

Hi! Great video showing a visual of how things work. Highly respect what you're doing. One note though, that you've forgot to mention when demonstrating the engagement point of the spring perch - as the fork/cartridge compresses, the cartridge cylinder as well as the spring will displace more and more oil the lower it gets into the stroke, meaning, the oil level will rise and the perch will engage higher in the stroke than what you've shown.

[@RideJBI]

Hello and thanks for the comment. You are spot on. Thank for you sharing that. I did overlook that detail during the video and it is important. I appreciate you bringing that to light.

[@robwhynott701]

Well done JB - the visual hammered home the oil height and its effects. 🤙🤙👍

[@RideJBI]

Thank you!

[@jay1871]

JB - if a rider simply wanted a little softer feel in the hands on chatter and square-edge chop, what would be the single most effective adjustment? Assume the rider is happy with the current shim stack and willing to live with whatever trade-offs come from increasing the comfort. Feel free to adjust the shim stack too (e.g. “use a lower diameter crossover shim”)

[@RideJBI]

The single most effective and easiest to adjust would be the comp clicker.

[@jay1871]

@ what would you address when that is not doing the trick? It helps but it’s like riding a water balloon.

[@mx724matthew]

Keep this fire coming!! Love these technical vids

[@RideJBI]

More where that came from!

[@tnearls]

Great info. Keep it coming!

[@raymondharold5973]

Another great teaching session. I asked a question before about WP Cone valve forks understanding you start @ 85 I still think you may have some feedback about oil height on the 65 cone valve, they only give one volume 195 cc it’s design is like a single chamber older KYB spring on top no mid spring pearch w/restriction so to speak (very small) almost free flow we found on the older single chamber style that adjusting the height had the desired increase in higher air spring rate as the fork descended without changing the first 2/3 of the stroke any noticeable difference looking at the volume of the spring in the fork @fully compressed state it’s not even close to hydraulic lock or any viable reason to not add oil to just effect the hold up a little but have a viable effect on the progressiveness of the last part of the travel my grandsons likes to flat land jumps when there’s time to be made up but we’ve gotten the chatter bump and mode stroke working pretty good by adding face shims to the base valve and adding a .030 thousands thk to the cone valve piston but the comp. Clicks need to be to far in to help slow down bottoming making the good part of the action feel not as compliant hurting cornering and transfers a harsh hand feel. All that said can you see why we can’t increase oil level say 5or10cc at a time to gain air spring compressed rate gains, because of the smaller fork ID I’m thinking 5cc increments is where I would start every other fork has a range on volume but I’ve searched and called a lot and they just state the pamphlet says 195 no min-max this can’t be the only height you think out of the box where performance gains are made, my grandson is strong and have for that class but he’s like Jeff Ward packaged like a Moto line backer what could l be missing on why there’s not a range but just a set point. It’s a big improvement over the stock old style air fork and most kids on 65 are 30-50 pounds lighter. With the damping rods on top your volume reducers would be a great solution but because of the configuration it doesn’t seem to be an option. By the way I’m in California and pretty plugged into the industry and those air volume parts you offer are a well kept secret by the lucky few who know the trade off of high oil levels and mid stroke harshness that results from the interaction with the spring stay contact coming in to soon for most riders. Summed up why a set point and not a range and would 5cc increments be responsible. Thanks for working hard to not just move shims around and say GIMMIE YOUR MONEY! Proud Grampa with a fast Grandson that’s doesn’t make excuses just try’s to improve and I need to keep up (or ahead) of his progression. ❤🙏💪🤔 Ps: is Bludd fork oil worth finding in California is that what you recommended and use?

[@RideJBI]

Thanks for comment! The blud oil is good stuff. We mainly use the KYB brand oil but the blud is our backup. You are spot on. With the small fork tube diameter the oil volume is more sensitive to smaller incremental changes. I’m not familiar with that specific fork but from what you have shared it sounds like you are on the right path.

[@raphaelbalachsan4764]

Thanks for sharing all this useful information 👍🏻👍🏻

[@RideJBI]

Thanks for tuning in!

[@KMFSPERFORMANCE599]

Great vid 🤙🏼 keep it up

[@RideJBI]

Thanks for tuning in!

[@MVPever]

Hello and happy new year! Thanks for this interesting video with the transparent fork stanchion. Not that I want to give you any responsibility for the answer, I'm just looking for a more expereinced opinion, but do you think that too much oil in KYB AOS could make the seals blow? I'm asking because I only left my AOS fork to drain for like 5 minutes before starting to put everything back together and then I've added 350 cc and I suspect I still had a significant amount of old oil inside. If I go to the MX track and I find out that the fork bottoms out too harsh it's not a big deal but I'm afraid I could blow seals...

[@RideJBI]

Thanks for the comment and watching. It could influence it but it’s unlikely that was the source of the issue.

[@MVPever]

@@RideJBI I mean, I haven't blown any seals yet, I've just changed the oil but now I suspect I hadn't let the fork drain enough before pouring the new oil in, that's all. I'm going to test the bike on some track with small jumps first so I'll see whether it feels harsh. Thank you for the reply.

[@black_sheep_fab9411]

Great friggin vid

[@RideJBI]

Thank you for tuning in!

[@ghost53pilot]

Super cool! Generally speaking air is compressible and fluid is not. Hence the value of both air and fluid in a fork.

[@RideJBI]

Thank you! Yes you are correct. Under these conditions the compressibility of fluids is very small so it’s not accounted for. But yes the air / gas is compressible and the change in volume / pressure is very noticeable.

[@grantmotox123]

the same experiment on the 24 wp CC fork would be cool. the perch is very different in that fork

[@RideJBI]

Good idea. And the hydro stop is much taller compared to the KYB.

[@grantmotox123]

@@RideJBI it’s huge I’ve contemplated modifying it

[@bwhaskell]

Curious. As you mentioned, the oil is splashing around the fork as you ride, and doesn't necessarily remain at the bottom of the fork. Does the bushing on the perch force all of oil to go through the perch instead of around it? I would think that since oil is splashing around that the level which the perch engages the oil and starts adding resistance could vary depending on how much oil is settled at bottom of the fork at that particular moment.

[@RideJBI]

Yes. The bushing does create a seal on the inside bore of the fork inner tube to help direct the oil through the perch. You are correct, as mentioned in the video the more oil volume the higher the average oil height will be during riding. The lesser oil volume the lower the average oil height will be during riding.

[@nikolasgibson3438]

Interested in the pro perch. I am curious on the behavior with 2+ successive bottom outs. On the first bottom out, the oil gets forced through the perch and provides a plush ramp up. However, the constrictive nature will prevent the oil from going back down quickly, and a second impact would result in almost no fork oil in the lower part of the leg. So unless it works as a one way valve, you’d have a significantly variable behavior on successive impacts. While the OEM one doesn’t provide the support on the first impact, the oil can easily flows back down for the second and provide more consistency. LMK

[@RideJBI]

You are correct. The Pro Perch bushing (not shown in the video) is a check valve that allows for proper back fill. The bushing can float / slide up and down. On compression stroke it covers the holes. On rebound slides down exposing the holes and providing additional volume for back fill. For more detail info please visit RideJBI.com.

[@nikolasgibson3438]

@@RideJBIawesome thanks! I’m always looking for bottom out resistance on my SSS bikes so this video was great. I definitely want to try the Pro Perch if I’m still searching after playing with oil levels.

[@grutzmac]

what are your thoughts on the massive hydrostop cup on the OEM WP XACT CC system? With that it seems impossible to use full travel on those forks... SICK VID!

[@RideJBI]

Thanks Aaron! For Moto it’s a good aggressive design. For off-road it’s a bit much. Meaning likely too much bottoming resistance for most off-road riders. But it’s still a new fork a lot still has to be learned.

[@manfredbuzek1922]

Thanks for the big Information. A Question: CRF 250 '24 is the Valving bad or the Stock Oil height.Thanks for you help.

[@RideJBI]

It’s a combo of both. The valving has room for improvement along with oil volume.

[@manfredbuzek1922]

@@RideJBI thanks for you help is 350 ml for 86 kg enough?

[@xXShadowProductions1]

Is it an even cheaper alternative for the perch to change to a more viscous oil for the outer chamber? (Leaving the oil height the same)

[@RideJBI]

It is possible to use a thicker oil in the outer chamber. The oil weight will determine how much additional compression resistance it creates. Over time the inner chamber oil and outer chamber oil will mix which isn’t ideal.

[@Stone881]

I assume that after establishing an oil level, that you could test different weights of oil to have some effect on the rate at which the fork moves through the stroke? Or are the weights of oil not really going to have any effect?

[@RideJBI]

Absolutely you can do that. The outer chamber oil and inner cartridge oil slowly mix over time. So we prefer to use the same oil in both chambers (outer and inner)

[@yz-pc9xi]

Whats the easiest way to lower fork oil height without taking them completely apart? Can u drain it thru the air bleed hole?

[@RideJBI]

Honestly unsure. If we are changing oil volume by reducing it. JB will pour out all the fork oil and the let the forks rest for a few hours to let all the oil drain out. Then pour back in the desired amount. Unfortunately I’m not aware of a faster way that is still accurate and repeatable.

[@yz-pc9xi]

@RideJBI I was afraid u were gonna say that lol. Thanks tho!

[@jesse_86_harley]

I currently have the 6500 kit in my WP explore Forks on KTM. My riding is single track. The wp manual recommends 380 mil external oil volume. What do you guys recommend?

[@LikeAPetrol]

JB, does it necessary for cartridge rod to be pushed down by pressure when cartridge body is assembled? If no, can it be described as malfunction?

[@RideJBI]

Hello. Yes. It should require pressure / force to compress the cartridge assembly down. And the cartridge rod will return / extend back out after. If this does not happen then that is a likely indication the cartridge seals need to be replaced.

[@michellatour150]

While commonly referred to as 'SSS', that is only a marketing term for the Yamaha version, they are KYB 48mm AOS forks.

[@RideJBI]

Yup. You are spot on correct. Since 2006. At this point is safe to use either term interchangeably as it refers to the same forks.

[@jaysmokey]

Not trying to go into the weeds here but hasn't the shape of the outer tubes changed slightly over the years but the fork name has stayed the same?

[@michellatour150]

@@jaysmokey Over the years there have been other changes like cartridge diameter, spring perch and midvalve etc. but the overall fork design is still named the KYB 48mm AOS. 'SSS' is a marketing term used by Yamaha, each manufacturer using this fork have their own proprietary internal settings.

[@ode4492]

Are travel indicators a good tool for judging how much oil you can add or remove? For instance. I just revalved a set of Beta KYB's to be more compliant and used the recommended 330cc's of oil and I still have approx 1.5" of stroke left after each ride according to my travel indicator. Can I keep dumping oil (10cc's at a time) till my indicator shows full stroke?

[@coldsteeloffroad]

You typically want to retain that last 1.5" of travel on your forks in reserve for HARD hits (is about where your bottoming cone comes into play and is also a safety measure to help protect your fork's internals from metal-to-metal contact). I'm talking the kind that don't normally happen unless a large mistake is made. If you were consistantly using less travel than that last 1.5" you could afford to go softer on compression.

[@RideJBI]

They are a helpful tool but don’t always tell the full story. Some forks will bottom out internally before the fork tube uses all the travel.

[@yodavizion]

Yeah dawg 🦾🏅

[@RideJBI]

Thanks Yoda!

[@otpipe]

What happened to episode 1? KZbin says it's hidden.

[@RideJBI]

You can watch episode 1 by clicking the link below: 👇🏼 kzbin.info/www/bejne/d16WgZtqo796ia8

[@justinfritz3635]

yo JB! I got a 06 rm250 and the suspension seems kinda lack luster. Is this a bike you know is well capable of good suspension or is it just out of date compared to newer stock stuff. 170lb guy here

[@RideJBI]

Hello and thanks for the comment. The stock suspension can surely be improved and perform much better than stock. However this does not imply the bike as a whole will perform on the same level as a newer bike. Meaning if your goal is to improve the bike as it sits now. Yes we can surely do that. If the goal is to make the bike feel like a new Yamaha YZ250 or something similar then it’s not possible be cause there are more factors then just the suspension that influence how a bike “feels”. I share this so we can make realistic expectations on how the bike would perform after a JBI Spec Revalve

[@CookieMonsterMeIs]

What would the effect be (what would the rider feel) if one fork leg had close to the max amount of oil and the other was well under the min amount of oil?

[@coldsteeloffroad]

Would be average bottoming resistance between the 2. Kind of like having a 5.0 spring in one leg & a 5.2 in the other averaging out to be a 5.1 overall. I'm sure running less than the minimum in any fork leg is a big no-no as it's required to ensure that the bottoming cone remains submerged in oil & will engage as a safety measure to protect the internals if the fork is bottomed hard.

[@RideJBI]

You can do that and it is something I’ve tried in the past. You can tell the difference but it was challenging to determine if it just felt different, if it was better or worse. Since it was not noticeablly better I didn’t pursue it further.

[@SreidMX]

Wouldn’t the fact that as the fork compresses create a pressurized environment and displace any sloshing oil to the bottom with any force?

[@RideJBI]

Not really. The air and oil just mix together creating bubbles within the oil until the fork equalizes allowing the two states of matter to separate again.

[@beccahughey]

I don't remember Bill Nye saying science like that!😮