How subtanks really work..

Jeremy Wilkey

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#1
Good question and well your the inspiration to finally put this one to the key pad.. So here goes.. Heres one for DRN as well as your reading...

As many of you have seen I've been a proponent of the Ross Maeda designed subtank system, and as anyone I know of who has asked my personal feeling everyone will hear.. "I won't ride a bike without a subtank system".. Yes I believe it does that much for a front suspension system.. So what's really going on.. Ross posted some stuff up for me on my web site a long time ago and I was excited to post it up.. It was a begging of a great friendship, that has made me a better tuner regardless of a few differences in approach.. But something was always a little off about what was going on inside the subtanks and that has left me uncomfortable.. Well one day, quite a while back it came to me as I was working on a Interceptor gas shock with my 12 ton press.....

So the subtanks work by regulating air through the restrictive barrier... Ok.. We run more oil which means that the fork will have a higher compression ratio and that will allow us to regulate the additional flow.. No worries.. But how does the system work as an advantage when we brake?(The subtanks feel much plusher than non-subtank fork when braking.) Like any fork with a higher oil level we should see more resistance to compression as we get deeper in the stroke..Interestingly enough many have said well its simple really the fork is not moving fast enough so the air can go through the restrictive barrier without much resistance.. And reason number two air is compressible and acts as a buffer...Humm.. This never set well with me.. Bottoming resistance is clearly slower in shaft speed than the huge (high speed) bumps at the bottom of the Reb-Bud ski jump, that you hit taped, before you brake.. That should spell death for the rider with a ultra high fork oil, and unlike a damping issue only that might help this is an ugly position sensitive... (this is not a prevention of packing going on..) Well I accepted common perspective till the VFR revealed something stupidly simple.

The tanks work because the forks are not fully extended for any length of time before the impact, and then have time to distribute a significant volume to the subtank without having time to refill the main chamber.(so it gets better the more bumps you hit if they are spaced closely and you've been in a wheelie for instance) So the pressure rise from static is not as nearly as significant as when we ride off into the air allowing the tanks to equalize and then land and force the almost complete volume into the tank..Its just a time delay.. The subtanks allow for a buffering, and bottoming resistance is increased because the forks fully extend and we are in the air long enough to empty any positive pressure back into the main fork volume.. How cool is that? So what else should this tell you? Don't buy anything with a check valve.. It will give the same bottoming effect, but you're not going to get the same plushness factor as the tanks will equalize more quickly and if your in big bumps, or you carry your wheel in the air too long your going to have issues.. It amazes me how designs can be so much more than they where intended for by chance alone..

BR,
Jer
 

bclapham

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#2
so how do they work with a showa twin chamber fork? i am not convinced the subtank the mutts nuts in this application

The chamber is sealed and the volume displaced by the damper rod is controlled by the ICS spring- thus, i dont understand that oil level (outer chamber) on a showa fork has any effect on damping rates. If we are slowing for a corner with the brake on and the fornt fork is compressed to the first 1/3 of the stroke- when we hit them braking bumps, we still have the 2nd third of the stroke to absorb them before we hit the 3rd third that is controlled by the airspring/oil level.
 

Jeremy Wilkey

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#3
Originally posted by bclapham
so how do they work with a showa twin chamber fork?

The chamber is sealed and the volume displaced by the damper rod is controlled by the ICS spring- thus, i dont understand that oil level (outer chamber) on a showa fork has any effect on damping rates.
Bruce,
Wether open or closed cartridge how do you invison the air spring having anything to do with damping rates?

BR,
Jer
 

bclapham

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#4
this is where i am confused about the whole deal, and all the hype and mis information only makes matters worse- i was led to beleive that the whole point of the airtanks was that on say a KYB fork (Enzos most popular fork) they enabled the user to run high oil levels without the harshness that would be assoicated with such a small airgap.
 

Jeremy Wilkey

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#5
BC,
Thats good! So lets get this cleared up.. Go back and read the string..Or the article on my web site, then look at the above post.. Then ponder it, then lets talk.. There is no such thing as hype here.. We are unhypeing it, once you see the big picture the benfits will become aparent without the hype..

The above is true but some logical questions should come up? How? Why? this is a controdiction to everything we know..

Thats my point, how? and why?.. Its a strange twist of luck maybe.. thats what I find intresting, and secondly, why the attempts to logically improve it have really sucked.. To me thats fun stuff... And whats best its a case where the practical types go well all your science does not work.When in reality its just the wrong scinece being applyed beacuse the question is not understood fully... I like that alot.. Unasnerable questions don't disprove science, they are only beckoning us farther down the trail to truth one small understanding at a time..

BR,
Jer
 
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#6
A revolution is upon us!
Is there any chance that we will see these things on factory(stock) bikes sometime in the future? I think that the sub tanks are a really good thing; however, they could be considerd a "band-aid" fix for poor suspension tuning. Wouldnt dialing in the valving BEFORE attaching the subtanks be more beneficial? At least then you would know that the tanks are in addition to good valving, instead of the tanks "fixing" valving that is inferior. A couple more questions to ponder...
 
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#7
Lets make sure that we are all on the same page as far as tank construction and plumbing is concerned. Jer, feel free to correct me if I am wrong.
The fork caps are tapped to accept a male-male fitting. A piece of SS braided hose with a female fitting is attached to the male-male fork cap fitting. The hose is then connected to the restrictive barrier valve. The other end of the valve(which is actually integral to the top of the tank) opens into the subtank. The tanks do not have a check valve type restrictive barrier; therefore, the air coming FROM the tanks back into the forks must pass through the same restrictions that the air coming form the forks into the tanks does. (the barrier restricts both ways)

Another thing:
When the shocks are in use some of the oil will accumulate in the sub tanks, correct? Does this affect the way that the tanks will work, or will feel?(not practically, but in theory) Or, since the oil is still contained in the system, does the system still remain the same? I would think that the smaller the tanks become(because of oil ingestion) the LESS effective the would become because of their decreased volume of air past the restrictive barrier.

Well, thats all for now, but I'll be back for more...
 
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#9
Originally posted by Jeremy Wilkey
Good question and well your the inspiration to finally put this one to the key pad.. So here goes.. Heres one for DRN as well as your reading...

So what else should this tell you? Don't buy anything with a check valve.. It will give the same bottoming effect, but you're not going to get the same plushness factor as the tanks will equalize more quickly and if your in big bumps, or you carry your wheel in the air too long your going to have issues.. It amazes me how designs can be so much more than they where intended for by chance alone..

BR,
Jer
I think this is an interesting opinion.....a friend has bought the TooTech set-up, so I guess I'll get to see how it works. :think:
 

Rcannon

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#10
Do the subranks work anythign like the forks Yamaha used in the late 70's? Remember the canisters that sat on top of the fork leg?
 

NO HAND

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#11
I was very interrested in Bruce's question about wether or not the sub tanks will work on a Showa fork. If I understand right, the article on Mx-tech web site says: the goal of the sub tank is to make the air spring speed sensitive. Since the Showa TC fork has a air spring in the spring chamber and is affected by oil volume in the spring chamber, does it mean the sub tank would be useful on the showa? I'm really wondering about this because I hate the fork on my stock 03cr250, so bad you have no idea. In the ads for the sub tank we always see it on kayaba and never on Showa.
 

NO HAND

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#12
Originally posted by Jeremy Wilkey


Bruce,
Wether open or closed cartridge how do you invison the air spring having anything to do with damping rates?

BR,
Jer
My first thought was that the damping rate was changed by the air spring because the oil is under more pressure as the fork compress. I was thinking that pressure is passed on the open cartridge but not to the closed one. But then, I don't know if the oil has a different damping curve when it is under pressure. If the oil has the same damping characteristics under whatever pressure. That would mean that open or closed cartridge would not make any difference when tuning the air spring?
 

NO HAND

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#13
I did a search on these air tanks and there are quit a few different brands on the market, some as low as 150$ Does anyone know if say for example the tech-care tanks are as good as the ones from enzo. I even found a post on a forum where they explained how to make your own, the guy used pvc and plumbing availlable locally. Is it that easy? I guess the tanks must be made to hold a precise volume of air. Another thing I came accross is that some companies claim the normal tank such the one from enzo would have issues with oil accumulation. Is that true?

It seems the too-tech model has overcome the oil accumulation by having the air inlet lower on the tank, but the design is flawed with the check-valve(as Jeremy explained). Anyway, the too-tech tank looks so ugly on a bike I doubt anyone would buy the product anyway. I'm thinking the best design would be two air tanks with the hose mounted on the bottom as to pull back the oil in the fork when it is extended. And also one without the check-valve. I haven't seen one like this.
 

bedell99

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#14
If I'm right the check valve's purpose in the too-tech design is to allow the rebound to not be affected. I think that would work better than a none check valve design. Either way the carbon fiber look of the enzo's do look the best.

Erik
 

NO HAND

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#15
Originally posted by bedell99
If I'm right the check valve's purpose in the too-tech design is to allow the rebound to not be affected. I think that would work better than a none check valve design. Either way the carbon fiber look of the enzo's do look the best.

Erik
The first post of this thread from Jeremy explains how the restriction is also helpful on the rebound stroke because it allows a delay before the tanks empty. This allows the fork to be softer on braking bumps; one thing the check valve equiped air tank won't be able to do as well.